Allied Telesis Switch AT 9924SP 30 User Manual
AlliedWareTM OS  
Configure EPSR (Ethernet Protection Switching  
Ring) to Protect a Ring from Loops  
How To |  
Introduction  
Putting a ring of Ethernet switches at the core of a network is a simple way to increase the  
network’s resilience—such a network is no longer susceptible to a single point of failure.  
However, the ring must be protected from Layer 2 loops. Traditionally, STP-based  
technologies are used to protect rings, but they are relatively slow to recover from link  
failure. This can create problems for applications that have strict loss requirements, such as  
voice and video traffic, where the speed of recovery is highly significant.  
This How To Note describes a fast alternative to STP: Ethernet Protection Switching Ring  
(EPSR). EPSR enables rings to recover rapidly from link or node failures—within as little as  
50ms, depending on port type and configuration. This is much faster than STP at 30 seconds  
or even RSTP at  
1
to 3 seconds.  
What information will you find in this document?  
This How To Note begins by describing EPSR in the following sections:  
•
•
•
•
•
"How EPSR Works" on page 3  
"Establishing a Ring" on page 4  
"Detecting a Fault" on page 5  
"Recovering from a Fault" on page 5  
"Restoring Normal Operation" on page 7  
Next it gives step-by-step configuration details and examples in the following sections:  
•
•
•
"How To Configure EPSR" on page 8  
"Example : A Basic Ring" on page 11  
1
"Example 2: A Double Ring" on page 14  
C613-16092-00 REV D  
www.alliedtelesis.com  
 
How EPSR Works  
How EPSR Works  
EPSR operates on physical rings of switches (note, not on  
meshed networks). When all nodes and links in the ring  
are up, EPSR prevents a loop by blocking data transmission  
across one port. When a node or link fails, EPSR detects  
the failure rapidly and responds by unblocking the blocked  
port so that data can flow around the ring.  
EPSR Components  
EPSR domain:  
A protection scheme for an  
Ethernet ring that consists of  
one or more data VLANs and a  
control VLAN.  
In EPSR, each ring of switches forms an EPSR domain.  
One of the domain’s switches is the master node and  
the others are transit nodes. Each node connects to the  
ring via two ports.  
Master node:  
The controlling node for a  
domain, responsible for polling  
the ring state, collecting error  
messages, and controlling the  
flow of traffic in the domain.  
One or more data VLANs sends data around the ring,  
and a control VLAN sends EPSR messages. A physical  
ring can have more than one EPSR domain, but each  
domain operates as a separate logical group of VLANs and  
has its own control VLAN and master node.  
Transit node:  
Other nodes in the domain.  
On the master node, one port is the primary port and  
the other is the secondary port. When all the nodes in  
the ring are up, EPSR prevents loops by blocking the data  
VLAN on the secondary port.  
Ring port:  
A port that connects the node  
to the ring. On the master node,  
each ring port is either the  
primary port or the secondary  
port. On transit nodes, ring  
ports do not have roles.  
The master node does not need to block any port on the  
control VLAN because loops never form on the control  
VLAN. This is because the master node never forwards  
any EPSR messages that it receives.  
Primary port:  
A ring port on the master node.  
This port determines the  
direction of the traffic flow, and  
is always operational.  
The following diagram shows a basic ring with all the  
switches in the ring up.  
End User Ports  
Control VLAN is forwarding  
Data VLAN is blocked  
Control VLAN is forwarding  
Data VLAN is forwarding  
Secondary port:  
A second ring port on the  
master node. This port remains  
active, but blocks all protected  
VLANs from operating unless  
the ring fails. Similar to the  
blocking port in an STP/RSTP  
instance.  
S
P
Master  
Node  
Transit  
Node  
4
Transit  
Node  
1
End User Ports  
End User Ports  
Control VLAN:  
Transit  
Node  
3
Transit  
Node  
2
The VLAN over which all  
control messages are sent and  
received. EPSR never blocks this  
VLAN.  
End User Ports  
End User Ports  
Data VLAN  
A VLAN that needs to be  
protected from loops. Each  
EPSR domain has one or more  
data VLANs.  
Control VLAN  
Control VLAN  
Data VLAN_1  
Data VLAN_2  
Primary Port  
P
S
Data VLAN_1  
Data VLAN_2  
Secondary Port  
epsr-basic-ring  
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How EPSR Works  
Establishing a Ring  
Once you have configured EPSR on the switches, the following steps complete the EPSR ring:  
1. The master node creates an EPSR Health message and sends it out the primary port. This  
increments the master node’s Transmit: Health counter in the show epsr count  
command.  
2. The first transit node receives the Health message on one of its two ring ports and, using  
a hardware filter, sends the message out its other ring port.  
Note that transit nodes never generate Health messages, only receive them and forward  
them with their switching hardware. This does not increment the transit node’s Transmit:  
Health counter. However, it does increment the Transmit counter in the show switch  
port command.  
The hardware filter also copies the Health message to the CPU. This increments the  
transit node’s Receive: Health counter. The CPU processes this message as required by  
the state machines, but does not send the message anywhere because the switching  
hardware has already done this.  
3. The Health message continues around the rest of the transit nodes, being copied to the  
CPU and forwarded in the switching hardware.  
4. The master node eventually receives the Health message on its secondary port. The  
master node's hardware filter copies the packet to the CPU (which increments the master  
node’s Receive: Health counter). Because the master received the Health message on its  
secondary port, it knows that all links and nodes in the ring are up.  
When the master node receives the Health message back on its secondary port, it resets  
the Failover timer. If the Failover timer expires before the master node receives the Health  
message back, it concludes that the ring must be broken.  
Note that the master node does not send that particular Health message out again. If it  
did, the packet would be continuously flooded around the ring. Instead, the master node  
generates a new Health message when the Hello timer expires.  
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How EPSR Works  
Detecting a Fault  
EPSR uses a fault detection scheme that alerts the ring  
when a break occurs, instead of using a spanning tree-  
like calculation to determine the best path. The ring  
then automatically heals itself by sending traffic over a  
protected reverse path.  
Master Node States  
Complete:  
The state when there are no link or  
node failures on the ring.  
EPSR uses the following two methods to detect when  
a transit node or a link goes down:  
Failed:  
The state when there is a link or  
node failure on the ring. This state  
indicates that the master node  
received a Link-Down message or  
that the failover timer expired before  
the master node’s secondary port  
received a Health message.  
•
Master node polling fault detection  
To check the condition of the ring, the master  
node regularly sends Health messages out its  
primary port, as described in "Establishing a  
Ring" on page 4. If all links and nodes in the ring are  
up, the messages arrive back at the master node on  
its secondary port.  
Transit Node States  
Idle:  
This can be a relatively slow detection method,  
because it depends on how often the node sends  
Health messages.  
The state when EPSR is first  
Note that the master node only ever sends Health  
messages out its primary port. If its primary port  
goes down, it does not send Health messages.  
configured, before the master node  
determines that all links in the ring  
are up. In this state, both ports on  
the node are blocked for the data  
VLAN. From this state, the node can  
move to Links Up or Links Down.  
•
Transit node unsolicited fault detection  
To speed up fault detection, EPSR transit nodes  
directly communicate when one of their interfaces  
goes down. When a transit node detects a fault at  
one of its interfaces, it immediately sends a Link-  
Down message over the link that remains up. This  
notifies the master node that the ring is broken and  
causes it to respond immediately.  
Links Up:  
The state when both the node’s ring  
ports are up and forwarding. From  
this state, the node can move to  
Links Down.  
Links Down:  
The state when one or both of the  
node’s ring ports are down. From this  
state, the node can move to Pre-  
forwarding  
Recovering from a Fault  
Fault in a link or a transit node  
When the master node detects an outage somewhere  
in the ring, using either detection method, it restores  
traffic flow by:  
Pre-forwarding:  
The state when both ring ports are  
up, but one has only just come up and  
is still blocked to prevent loops. From  
this state, the transit node can move  
to Links Up if the master node blocks  
its secondary port, or to Links Down  
if another port goes down.  
1. declaring the ring to be in a Failed state  
2. unblocking its secondary port, which enables data  
VLAN traffic to pass between its primary and  
secondary ports  
3. flushing its own forwarding database (FDB) for the  
two ring ports  
4. sending an EPSR Ring-Down-Flush-FDB control message to all the transit nodes, via  
both its primary and secondary ports  
The transit nodes respond to the Ring-Down-Flush-FDB message by flushing their  
forwarding databases for each of their ring ports. As the data starts to flow in the ring’s  
Page 5 | AlliedWare™ OS How To Note: EPSR  
 
   
How EPSR Works  
new configuration, the nodes (master and transit) re-learn their layer 2 addresses. During  
this period, the master node continues to send Health messages over the control VLAN.  
This situation continues until the faulty link or node is repaired.  
For a multidomain ring, this process occurs separately for each domain within the ring.  
The following figure shows the flow of control frames when a link breaks.  
Control VLAN is forwarding  
Data VLANs move from blocking  
to forwarding  
Control VLAN is forwarding  
Data VLANs are forwarding  
3
S
P
2
1
Master  
Node  
Transit  
Node  
4
Transit  
Node  
1
Transit  
Node  
3
Transit  
Node  
2
Data ports move from  
fowarding to blocking  
1
2
3
Master Node Health Message  
Transit Node Link-Down Message  
Ring-Down-Flush-FDB Message  
Control VLAN  
epsr-broken-ring  
Fault in the master node  
If the master node goes down, the transit nodes simply continue forwarding traffic around  
the ring—their operation does not change.  
The only observable effects on the transit nodes are that:  
•
•
They stop receiving Health messages and other messages from the master node.  
The transit nodes connected to the master node experience a broken link, so they send  
Link-Down messages. If the master node is down these messages are simply dropped.  
Neither of these symptoms affect how the transit nodes forward traffic.  
Once the master node recovers, it continues its function as the master node.  
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How EPSR Works  
Restoring Normal Operation  
Master Node  
Once the fault has been fixed, the master node’s Health messages traverse the whole ring and  
arrive at the master node’s secondary port. The master node then restores normal  
conditions by:  
1. declaring the ring to be in a state of Complete  
2. blocking its secondary port for data VLAN traffic (but not for the control VLAN)  
3. flushing its forwarding database for its two ring ports  
4. sending a Ring-Up-Flush-FDB message from its primary port, to all transit nodes.  
Transit Nodes with One Port Down  
As soon as the fault has been fixed, the transit nodes on each side of the (previously) faulty  
link section detect that link connectivity has returned. They change their ring port state from  
Links Down to Pre-Forwarding, and wait for the master node to send a Ring-Up-Flush-FDB  
control message.  
Once these transit nodes receive the Ring-Up-Flush-FDB message, they:  
•
•
flush the forwarding databases for both their ring ports  
change the state of their ports from blocking to forwarding for the data VLAN, which  
allows data to flow through their previously-blocked ring ports  
The transit nodes do not start forwarding traffic on the previously-down ports until after  
they receive the Ring-Up-Flush-FDB message. This makes sure the previously-down transit  
node ports stay blocked until after the master node blocks its secondary port. Otherwise,  
the ring could form a loop because it had no blocked ports.  
Transit Nodes with Both Ports Down  
The Allied Telesis implementation includes an extra feature to improve handling of double  
link failures. If both ports on a transit node are down and one port comes up, the node:  
1. puts the port immediately into the forwarding state and starts forwarding data out that  
port. It does not need to wait, because the node knows there is no loop in the ring—  
because the other ring port on the node is down  
2. remains in the Links Down state  
3. starts a DoubleFailRecovery timer with a timeout of four seconds  
4. waits for the timer to expire. At that time, if one port is still up and one is still down, the  
transit node sends a Ring-Up-Flush-FDB message out the port that is up. This message is  
usually called a “Fake Ring Up message”.  
Sending this message allows any ports on other transit nodes that are blocking or in the Pre-  
forwarding state to move to forwarding traffic in the Links Up state. The timer delay lets the  
device at the other end of the link that came up configure its port appropriately, so that it is  
ready to receive the transmitted message.  
Note that the master node would not send a Ring-Up-Flush-FDB message in these  
circumstances, because the ring is not in a state of Complete. The master node’s secondary  
port remains unblocked.  
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How To Configure EPSR  
How To Configure EPSR  
This section first outlines, step-by-step, how to configure EPSR. Then it discusses changing  
the settings for the control VLAN, if you need to do this after initial configuration.  
Configuring EPSR  
1. Connect your switches into a ring  
EPSR does not in itself limit the number of nodes that can exist on any given ring. Each switch  
can participate in up to 16 rings.  
If you already have a ring in a live network, disconnect the cable between any two of the  
nodes before you start configuring EPSR, to prevent a loop.  
2. On each switch, configure EPSR  
On each switch, perform the following configuration steps. Configuration of the master node  
and each transit node is very similar.  
i. Configure the control VLAN  
This step creates the control VLAN and adds the ring ports to it as tagged ports.  
Enter the commands:  
create vlan=control-vlan-name vid=control-vid  
add vlan=control-vid port=ring-ports frame=tagged  
Note that you can use trunk groups for the ring ports.  
ii. Configure the data VLAN  
This step creates the data VLAN (or VLANs—you can have as many as you want) and  
adds the ring ports as tagged ports.  
Enter the commands:  
create vlan=data-vlan-name vid=data-vid  
add vlan=data-vid port=ring-ports frame=tagged  
The two ring ports must belong to the control VLAN and all data VLANs.  
Page 8 | AlliedWare™ OS How To Note: EPSR  
 
 
How To Configure EPSR  
iii. Remove the ring ports from the default VLAN  
If you leave all the ring ports in the default VLAN (vlan1), they will create a loop, unless  
vlan  
1
is part of the EPSR domain. To avoid loops, you need to do one of the following:  
make vlan a data VLAN, or  
remove the ring ports from vlan  
remove at least one of the ring ports from vlan  
•
•
•
1
1
, or  
1
on at least one of the switches.  
We do not recommend this option, because the action you have taken is less  
obvious when maintaining the network later.  
In this How To Note, we remove the ring ports from the default VLAN. Use the  
command:  
delete vlan=1 port=ring-ports  
iv. Configure the EPSR domain  
This step creates the domain, specifying whether the switch is the master node or a  
transit node. It also specifies which VLAN is the control VLAN, and on the master node  
which port is the primary port.  
Enter one of the following commands:  
On the master node:  
create epsr=name mode=master controlvlan=control-vlan-name  
primaryport=port-number  
On each transit node:  
create epsr=name mode=transit controlvlan=control-vlan-name  
This step also adds the data VLAN to the domain. Enter the command:  
add epsr=name datavlan=data-vlan-name  
v. Enable EPSR  
This step enables the domain on each switch. Enter the command:  
enable epsr=name  
3. Configure other ports and protocols as required  
On each switch, configure the other ports and protocols that are required for your network.  
Page 9 | AlliedWare™ OS How To Note: EPSR  
 
How To Configure EPSR  
Modifying the Control VLAN  
You cannot modify the control VLAN while EPSR is enabled. If you try to remove or add  
ports to the control VLAN, the switch generates an error message as follows:  
Manager> delete vlan=1000 port=1  
Error (3089409): VLAN 1000 is a control VLAN in EPSR and cannot be modified  
Disable the EPSR domain and then make the required changes. Note that disabling EPSR will  
create a loop, so is not recommended on a network with live data. Of course, in a live  
network, you can manually prevent a loop by disconnecting the cable between any two of the  
nodes.  
Page 10 | AlliedWare™ OS How To Note: EPSR  
 
 
Example 1: A Basic Ring  
Example 1: A Basic Ring  
This example builds a simple 3-switch ring with one data VLAN, as shown in the following  
diagram. Control packets are transmitted around the ring on vlan1000 and data packets on  
vlan2.  
End User Ports  
port 1: primary  
port 2: secondary  
P
S
Master  
Node  
(A)  
port 1: ring  
port 1: ring  
End User Ports  
End User Ports  
port 2: ring  
port 2: ring  
Transit  
Node  
(B)  
Transit  
Node  
(C)  
epsr-example-basic-ring  
Configure the Master Node (A)  
1. Create the control VLAN  
create vlan=vlan1000 vid=1000  
2. Add the ring ports to the control VLAN  
add vlan=1000 port=1-2 frame=tagged  
3. Create the data VLAN  
create vlan=vlan2 vid=2  
4. Add the ring ports to the data VLAN  
The two ring ports must belong to the control VLAN and all data VLANs.  
add vlan=2 port=1-2 frame=tagged  
Page 11 | AlliedWare™ OS How To Note: EPSR  
 
 
Example 1: A Basic Ring  
5. Remove the ring ports from the default VLAN  
delete vlan=1 port=1-2  
6. Create the EPSR domain  
This step creates the domain, specifying that this switch is the master node. It also specifies  
which VLAN is the control VLAN and which port is the primary port.  
create epsr=test mode=master controlvlan=vlan1000 primaryport=1  
7. Add the data VLAN to the domain  
add epsr=test datavlan=vlan2  
8. Enable EPSR  
enable epsr=test  
Configure the Transit Nodes (B and C)  
Each of the transit nodes has the same EPSR configuration in this example.  
1. Create the control VLAN  
create vlan=vlan1000 vid=1000  
2. Add the ring ports to the control VLAN  
add vlan=1000 port=1-2 frame=tagged  
3. Create the data VLAN  
create vlan=vlan2 vid=2  
4. Add the ring ports to the data VLAN  
The two ring ports must belong to both the control VLAN and all data VLANs.  
add vlan=2 port=1-2 frame=tagged  
5. Remove the ring ports from the default VLAN  
delete vlan=1 port=1-2  
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Example 1: A Basic Ring  
6. Create the EPSR domain  
This step creates the domain, specifying that this switch is the transit node. It also specifies  
which VLAN is the control VLAN.  
create epsr=test mode=transit controlvlan=vlan1000  
7. Add the data VLAN to the domain  
add epsr=test datavlan=vlan2  
8. Enable EPSR  
enable epsr=test  
Page 13 | AlliedWare™ OS How To Note: EPSR  
 
Example 2: A Double Ring  
Example 2: A Double Ring  
This example adds to the previous ring by making two domains, as shown in the following  
diagram.  
Master  
Node  
(A)  
Master  
Node  
(C)  
port 4:  
primary  
port 1:  
primary  
port 2:  
secondary  
port 5:  
secondary  
port 1  
port 2  
port 4  
port 5  
Domain 1  
control VLAN: 1000  
data VLAN: 2  
Domain 2  
control VLAN: 40  
data VLAN: 50  
Transit  
Node  
(E)  
port 4  
port 1  
port 2  
port 5  
Transit  
Node  
(B)  
Transit  
Node  
(D)  
epsr-example-double-ring  
1. Configure the master node (switch A) for domain  
1
The master node for domain  
domain has been renamed).  
1
is the same as in the previous example (except that the  
create vlan=vlan1000 vid=1000  
add vlan=1000 port=1-2 frame=tagged  
create vlan=vlan2 vid=2  
add vlan=2 port=1-2 frame=tagged  
delete vlan=1 port=1-2  
create epsr=domain1 mode=master controlvlan=vlan1000 primaryport=1  
add epsr=domain1 datavlan=vlan2  
enable epsr=domain1  
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Example 2: A Double Ring  
2. Configure the transit node (switch B) that belongs just to domain  
1
This transit node is the same as in the previous example (except that the domain has been  
renamed).  
create vlan=vlan1000 vid=1000  
add vlan=1000 port=1-2 frame=tagged  
create vlan=vlan2 vid=2  
add vlan=2 port=1-2 frame=tagged  
delete vlan=1 port=1-2  
create epsr=domain1 mode=transit controlvlan=vlan1000  
add epsr=domain1 datavlan=vlan2  
enable epsr=domain1  
3. Configure the master node (switch C) for domain 2  
Configure the control VLAN:  
create vlan=vlan40 vid=40  
add vlan=40 port=4-5 frame=tagged  
Configure the data VLAN:  
create vlan=vlan50 vid=50  
add vlan=50 port=4-5 frame=tagged  
Remove the ring ports from the default VLAN:  
delete vlan=1 port=4-5  
Configure EPSR:  
create epsr=domain2 mode=master controlvlan=vlan40 primaryport=4  
add epsr=domain2 datavlan=vlan50  
enable epsr=domain2  
4. Configure the transit node (switch D) that belongs just to domain 2  
Configure the control VLAN:  
create vlan=vlan40 vid=40  
add vlan=40 port=4-5 frame=tagged  
Configure the data VLAN:  
create vlan=vlan50 vid=50  
add vlan=50 port=4-5 frame=tagged  
Remove the ring ports from the default VLAN:  
delete vlan=1 port=4-5  
Page 15 | AlliedWare™ OS How To Note: EPSR  
 
Example 2: A Double Ring  
Configure EPSR:  
create epsr=domain2 mode=transit controlvlan=vlan40  
add epsr=domain2 datavlan=vlan50  
enable epsr=domain2  
5. Configure the transit node (switch E) that belongs to both domains  
Two separate EPSR domains are configured on this switch.  
Configure the control VLAN for domain  
1:  
create vlan=vlan1000 vid=1000  
add vlan=1000 port=1-2 frame=tagged  
Configure the control VLAN for domain 2:  
create vlan=vlan40 vid=40  
add vlan=40 port=4-5 frame=tagged  
Configure the data VLAN for domain  
1:  
create vlan=vlan2 vid=2  
add vlan=2 port=1-2 frame=tagged  
Configure the data VLAN for domain 2:  
create vlan=vlan50 vid=50  
add vlan=50 port=4-5 frame=tagged  
Remove the ring ports from the default VLAN:  
delete vlan=1 port=1-2,4-5  
Configure EPSR for domain 1. This switch is a transit node:  
create epsr=domain1 mode=transit controlvlan=vlan1000  
add epsr=domain1 datavlan=vlan2  
enable epsr=domain1  
Configure EPSR for domain 2. This switch is a transit node:  
create epsr=domain2 mode=transit controlvlan=vlan40  
add epsr=domain2 datavlan=vlan50  
enable epsr=domain2  
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Example 3: EPSR and RSTP  
Example 3: EPSR and RSTP  
This example uses EPSR to protect one ring and RSTP to protect another overlapping ring.  
RSTP  
Master  
Switch  
Node  
(C)  
port 1:  
primary  
(A)  
port 10  
port 2:  
port 11  
secondary  
port 1  
port 2  
port 10  
port 11  
Domain 1  
RSTP:  
control VLAN: 1000  
data VLAN: 2  
STP VLAN: 10  
Switch  
(E)  
port 1  
port 10  
port 2  
port 11  
RSTP  
Switch  
(D)  
Transit  
Node  
(B)  
epsr-example-rstp  
1. Configure the master node (switch A) for the EPSR domain  
The master node is the same as in the previous example.  
create vlan=vlan1000 vid=1000  
add vlan=1000 port=1-2 frame=tagged  
create vlan=vlan2 vid=2  
add vlan=2 port=1-2 frame=tagged  
delete vlan=1 port=1-2  
create epsr=domain1 mode=master controlvlan=vlan1000 primaryport=1  
add epsr=domain1 datavlan=vlan2  
enable epsr=domain1  
Page 17 | AlliedWare™ OS How To Note: EPSR  
 
 
Example 3: EPSR and RSTP  
2. Configure the transit node (switch B) that belongs just to the EPSR domain  
This transit node (B) is the same as in the previous example.  
create vlan=vlan1000 vid=1000  
add vlan=1000 port=1-2 frame=tagged  
create vlan=vlan2 vid=2  
add vlan=2 port=1-2 frame=tagged  
delete vlan=1 port=1-2  
create epsr=domain1 mode=transit controlvlan=vlan1000  
add epsr=domain1 datavlan=vlan2  
enable epsr=domain1  
3. Configure the switches that belong to the RSTP instance (switches C and D)  
Switches C and D have the same configuration in this example.  
Configure the STP VLAN:  
create vlan=vlan10 vid=10  
add vlan=10 port=10-11 frame=tagged  
Remove the STP VLAN’s ports from the default VLAN:  
delete vlan=1 port=10-11  
Configure STP:  
create stp=example  
add stp=example vlan=vlan10  
enable stp=example  
set stp=example mode=rapid  
Page 18 | AlliedWare™ OS How To Note: EPSR  
 
Example 3: EPSR and RSTP  
4. Configure switch E for EPSR and RSTP  
Configure the control VLAN for EPSR:  
create vlan=vlan1000 vid=1000  
add vlan=1000 port=1-2 frame=tagged  
Configure the data VLAN for EPSR:  
create vlan=vlan2 vid=2  
add vlan=2 port=1-2 frame=tagged  
Remove the ring ports from the default VLAN:  
delete vlan=1 port=1-2  
Configure EPSR:  
create epsr=domain1 mode=transit controlvlan=vlan1000  
add epsr=domain1 datavlan=vlan2  
enable epsr=domain1  
Configure the STP VLAN:  
create vlan=vlan10 vid=10  
add vlan=10 port=10-11 frame=tagged  
Remove the STP VLAN’s ports from the default VLAN:  
delete vlan=1 port=10-11  
Configure STP:  
create stp=example  
add stp=example vlan=vlan10  
enable stp=example  
set stp=example mode=rapid  
Page 19 | AlliedWare™ OS How To Note: EPSR  
 
Example 4: EPSR with Nested VLANs  
Example 4: EPSR with Nested VLANs  
In this example:  
•
•
•
•
•
client switches A and C are in the same end-user VLAN (vlan20)  
client switches B and D are in the same end-user VLAN (vlan200)  
traffic for vlan20 and vlan200 is nested inside vlan50 for transmission around the core  
vlan50 is the data VLAN for the EPSR domain  
vlan  
1
00 is the control VLAN for the EPSR domain  
Client  
Switch  
(E)  
Client  
Switch  
(H)  
port 20  
port 10  
port 22  
port 22  
port 2:  
secondary  
port 2  
Master  
Node  
(A)  
Transit  
Node  
(D)  
port 1  
port 1:  
primary  
EPSR Domain  
control VLAN: 100  
data VLAN: 50  
Transit  
Node  
(B)  
Transit  
Node  
(C)  
port 1  
port 1  
port 2  
port 2  
port 22  
port 22  
port 10  
port 20  
Client  
Switch  
(F)  
Client  
Switch  
(G)  
epsr-example-nested  
Page 20 | AlliedWare™ OS How To Note: EPSR  
 
 
Example 4: EPSR with Nested VLANs  
1. Configure the master node (switch A) for the EPSR domain  
Configure the EPSR control VLAN:  
create vlan=vlan100 vid=100  
add vlan=100 port=1-2 frame=tagged  
Configure vlan50. This VLAN acts as both the nested VLAN and the EPSR data VLAN. The  
following commands create vlan50 and configure it as a nested VLAN:  
create vlan=vlan50 vid=50 nested  
add vlan=50 port=22 nestedtype=customer  
add vlan=50 port=1-2 nestedtype=core  
Remove the ring ports from the default VLAN:  
delete vlan=1 port=1-2  
Configure EPSR:  
create epsr=example mode=master controlvlan=vlan100 primaryport=1  
add epsr=example datavlan=vlan50  
enable epsr=example  
2. Configure the transit nodes (switches B, C and D) for the EPSR domain  
Each of the transit nodes has the same EPSR configuration in this example.  
Configure the EPSR control VLAN:  
create vlan=vlan100 vid=100  
add vlan=100 port=1-2 frame=tagged  
Configure vlan50, which acts as both the nested VLAN and the EPSR data VLAN:  
create vlan=vlan50 vid=50 nested  
add vlan=50 port=22 nestedtype=customer  
add vlan=50 port=1-2 nestedtype=core  
Remove the ring ports from the default VLAN:  
delete vlan=1 port=1-2  
Configure EPSR:  
create epsr=example mode=transit controlvlan=vlan100  
add epsr=example datavlan=vlan50  
enable epsr=example  
Page 21 | AlliedWare™ OS How To Note: EPSR  
 
Example 4: EPSR with Nested VLANs  
3. Configure client switch E (connected to the master node)  
create vlan=vlan20 vid=20  
add vlan=20 port=20 frame=tagged  
enable ip  
add ip interface=vlan20 ip=192.168.20.10  
4. Configure client switch F (connected to transit node B)  
create vlan=vlan200 vid=200  
add vlan=200 port=10 frame=tagged  
enable ip  
add ip interface=vlan200 ip=192.168.200.1  
5. Configure client switch G (connected to transit node C)  
create vlan=vlan20 vid=20  
add vlan=20 port=20 frame=tagged  
enable ip  
add ip int=vlan20 ip=192.168.20.1  
6. Configure client switch H (connected to transit node D)  
create vlan=vlan200 vid=200  
add vlan=200 port=10 frame=tagged  
enable ip  
add ip interface=vlan200 ip=192.168.200.10  
Page 22 | AlliedWare™ OS How To Note: EPSR  
 
Example 5: EPSR with management stacking  
Example 5: EPSR with management stacking  
In this example:  
•
three switches are stacked together, so you can manage all three switches by entering  
commands into the CLI of any one of them  
•
•
the three switches are also configured as an EPSR domain  
vlan1000 is used as the stacking VLAN and as the EPSR control VLAN. Stacked switches  
use the stacking VLAN to communicate with each other  
•
•
the data VLAN for EPSR is vlan20  
ports on the stacked switches are numbered using the stacking scheme of hostid.0.port  
vlan45  
P
S
port 1.0.1:  
primary  
port 1.0.2:  
secondary  
Master  
Node  
(host1)  
port 2.0.1  
port 3.0.1  
Transit  
Node  
(host2)  
Transit  
Node  
(host3)  
port 2.0.2  
port 3.0.2  
vlan30  
epsr-example-stack  
Page 23 | AlliedWare™ OS How To Note: EPSR  
 
 
Example 5: EPSR with management stacking  
1. Configure stacking on the master node for the EPSR domain (host  
1)  
The following commands must be entered into the CLI of this particular switch.  
First, give the switch a host ID number so that the stack can identify it:  
set system hostid=1 serialnumber=12345678  
set system name=host1  
Create the stacking VLAN and add the ring ports to it. Note the port numbering notation—  
these are ports and 2 on stacking host . Because this VLAN will also be the EPSR control  
1
1
VLAN, this step also adds the ring ports to the control VLAN. Use the commands:  
create vlan=stack vid=1000  
add vlan=1000 port=1.0.1-1.0.2 frame=tagged  
delete vlan=1 port=1.0.1-1.0.2  
Add the stacking VLAN to the stack and enable stacking:  
add stack interface=vlan1000  
enable stack  
2. Configure stacking on the first transit node (host2)  
These commands must be entered into the CLI of this particular switch.  
set system hostid=2 serialnumber=23456789  
set system name=host2  
create vlan=stack vid=1000  
add vlan=1000 port=2.0.1-2.0.2 frame=tagged  
delete vlan=1 port=2.0.1-2.0.2  
add stack interface=vlan1000  
enable stack  
3. Configure stacking on the second transit node (host3)  
These commands must be entered into the CLI of this particular switch.  
set system hostid=3 serialnumber=34567890  
set system name=host3  
create vlan=stack vid=1000  
add vlan=1000 port=3.0.1-3.0.2 frame=tagged  
delete vlan=1 port=3.0.1-3.0.2  
add stack interface=vlan1000  
enable stack  
Page 24 | AlliedWare™ OS How To Note: EPSR  
 
Example 5: EPSR with management stacking  
4. Configure the other VLANs on the stacked switches  
The stack now exists, so you can configure all three switches from the CLI of the master  
node (or any other of the switches). However, the ports and IP addresses are different for  
each switch, so you need to make most of the commands host-directed.  
Create the EPSR data VLAN. This command will propagate to all three switches:  
create vlan=vlan20 vid=20  
Assign ports and an IP address to the data VLAN on each switch. You can type the following  
commands into any switch in the stack. To apply them to the correct switches, make them  
host-directed by starting each command with the host ID number of the target switch.  
Therefore, use the following commands:  
1: add vlan=20 port=1.0.1-1.0.2 frame=tagged  
1: add ip int=vlan20 ip=192.168.20.1  
2: add vlan=20 port=2.0.1-2.0.2 frame=tagged  
2: add ip int=vlan20 ip=192.168.20.2  
3: add vlan=20 port=3.0.1-3.0.2 frame=tagged  
3: add ip int=vlan20 ip=192.168.20.3  
Configure other VLANs as required. In this example, two of the switches have other VLANs  
attached:  
1: create vlan=vlan45 vid=45  
1: add vlan=45 port=1.0.23-1.0.24 frame=tagged  
1: add ip int=vlan45 ip=192.168.45.1  
2: create vlan=vlan30 vid=30  
2: add vlan=30 port=2.0.10 frame=tagged  
2: add ip int=vlan30 ip=192.168.30.1  
Enable IP on the whole stack:  
enable ip  
5. Configure EPSR on the stacked switches  
Create the EPSR domain:  
1: create epsr=example mode=master controlvlan=stack primary=1.0.1  
2: create epsr=example mode=transit controlvlan=stack  
3: create epsr=example mode=transit controlvlan=stack  
Specify the data VLAN:  
add epsr=example datavlan=vlan20  
Enable the EPSR domain:  
enable epsr=example  
Page 25 | AlliedWare™ OS How To Note: EPSR  
 
Example 6: EPSR with an iMAP  
Example 6: EPSR with an iMAP  
This example is the same as "Example  
three switches is an iMAP. We used an AT-TN7  
the iMAP are 5.0 and 5. . The example first shows the configuration script for the iMAP as  
the master node, then as the transit node. For the configuration of the other two switches,  
see Example  
1
: A Basic Ring" on page 11 except that one of the  
1
00 iMAP running 6. 0. The ring ports on  
1.1  
1
1.  
Configure the AT-TN7100 iMAP as Master Node  
The following diagram shows a partial script for the iMAP, with the commands for configuring  
it as a EPSR master node and other relevant commands.  
ADD IP INTERFACE=MGMT IPADDRESS=172.28.9.3 SUBNETMASK=255.255.255.0  
CARD=ACTCFC GATEWAY=172.28.9.1  
#
SET SWITCH AGEINGTIMER=300  
#
SET SYSTEM PROVMODE=AUTO  
SET SYSTEM GATEWAY=172.28.9.1  
#
CREATE EPSR=test MASTER HELLOTIME=1 FAILOVERTIME=2 RINGFLAPTIME=0  
#
CREATE VLAN=vlan2 VID=2 FORWARDINGMODE=STD  
CREATE VLAN=vlan1000 VID=1000 FORWARDINGMODE=STD  
#
ADD VLAN=2 INTERFACE=ETH:[5.0-1] FRAME=TAGGED  
ADD VLAN=1000 INTERFACE=ETH:[5.0-1] FRAME=TAGGED  
#
DELETE VLAN=1 INTERFACE=ETH:[5.0-1]  
#
SET INTERFACE=ETH:[5.0-1] ACCEPTABLE=VLAN  
#
ADD EPSR=test INTERFACE=ETH:[5.0] TYPE=PRIMARY  
ADD EPSR=test INTERFACE=ETH:[5.1] TYPE=SECONDARY  
ADD EPSR=test VLAN=1000 TYPE=CONTROL  
ADD EPSR=test VLAN=2 TYPE=DATA  
#
ENABLE EPSR=test  
Page 26 | AlliedWare™ OS How To Note: EPSR  
 
 
Example 6: EPSR with an iMAP  
Checking the Master Node Configuration  
To see a summary, use the command:  
show epsr  
The following diagram shows the expected output.  
--- EPSR Domain Information ---------------------------------------------------  
EPSR Domain Node Type Domain Status/ Control Interface(s) (PhysicalState,  
State  
Vlan  
Type, State)  
--------------- --------- --------------- ------- ----------------------------  
test  
MASTER  
EN/COMPLETE  
1000 5.0 (UP,DNSTRM,FWDING ),  
5.1 (UP,DNSTRM,BLOCKED)  
-------------------------------------------------------------------------------  
To see details, use the command:  
show epsr=test  
The following diagram shows the expected output.  
--- EPSR Domain Information ---------------------------------------------------  
EPSR Domain Name...................... test  
EPSR Domain Node Type................. Master  
EPSR Domain State..................... COMPLETE  
MAC Address of Master Node............ 00:00:CD:28:06:19  
EPSR Domain Status.................... Enabled  
Control Vlan.......................... 1000  
Primary Interface..................... 5.0  
Physical State of Primary Interface... UP  
Primary Interface Type................ DOWNSTREAM  
Primary Interface State............... FORWARDING  
Secondary Interface................... 5.1  
Physical State of Secondary Interface. UP  
Secondary Interface Type.............. DOWNSTREAM  
Secondary Interface State............. BLOCKED  
Hello Timer (seconds.................. 1  
Failover Timer (seconds).............. 2  
RingFlap Timer (seconds).............. 0  
Hello Time Remaining (seconds)........ 1  
Failover Time Remaining (seconds)..... 0  
RingFlap Time Remaining (seconds)..... 0  
Hello Sequence........................ 526  
Data Vlans............................ 2  
-------------------------------------------------------------------------------  
Page 27 | AlliedWare™ OS How To Note: EPSR  
 
Example 6: EPSR with an iMAP  
Configure the AT-TN7100 iMAP as a Transit Node  
The following diagram shows a partial script for the iMAP, with the commands for configuring  
it as a transit node.  
CREATE EPSR=test TRANSIT  
#
CREATE VLAN=vlan2 VID=2 FORWARDINGMODE=STD  
CREATE VLAN=vlan1000 VID=1000 FORWARDINGMODE=STD  
#
DISABLE INTERFACE=0.0-0.15,1.0-1.15,2.0-2.15,4.0-4.1,5.0-5.1  
#
ADD VLAN=2 INTERFACE=ETH:[5.0-1] FRAME=TAGGED  
ADD VLAN=1000 INTERFACE=ETH:[5.0-1] FRAME=TAGGED  
#
DELETE VLAN=1 INTERFACE=ETH:[5.0-1]  
#
SET INTERFACE=0.0-0.15,1.0-1.15,2.0-2.15,4.0-4.1,5.0-5.1  
PROFILE=AutoProv  
SET INTERFACE=ETH:[5.0-1] ACCEPTABLE=VLAN  
#
ADD EPSR=test INTERFACE=ETH:[5.0-1]  
ADD EPSR=test VLAN=1000 TYPE=CONTROL  
ADD EPSR=test VLAN=2 TYPE=DATA  
#
ENABLE EPSR=test  
#
ENABLE INTERFACE=0.0-0.15,1.0-1.15,2.0-2.15,4.0-4.1,5.0-5.1  
Checking the Transit Node Configuration  
To see a summary, use the command:  
show epsr  
The following diagram shows the expected output.  
--- EPSR Domain Information ---------------------------------------------------  
EPSR Domain Node Type Domain Status/ Control Interface(s) (PhysicalState,  
State  
Vlan  
Type, State)  
--------------- --------- --------------- ------- ----------------------------  
test  
TRANSIT  
EN/LINKS-UP  
1000 5.0 (UP,UPSTRM,FWDING ),  
5.1 (UP,DNSTRM,FWDING )  
-------------------------------------------------------------------------------  
Page 28 | AlliedWare™ OS How To Note: EPSR  
 
Classifiers and Hardware Filters  
To see details, use the command:  
show epsr=test  
The following diagram shows the expected output.  
--- EPSR Domain Information ---------------------------------------------------  
EPSR Domain Name...................... test  
EPSR Domain Node Type................. Transit  
EPSR Domain State..................... LINKS-UP  
MAC Address of Master Node............ 00:00:CD:24:02:4F  
EPSR Domain Status.................... Enabled  
Control Vlan.......................... 1000  
Ring Interface # 1.................... 5.0  
Physical State of Ring Interface # 1.. UP  
Ring Interface # 1 Type............... UPSTREAM  
Ring Interface # 1 State.............. FORWARDING  
Ring Interface # 2.................... 5.1  
Physical State of Ring Interface # 2.. UP  
Ring Interface # 2 Type............... DOWNSTREAM  
Ring Interface # 2 State.............. FORWARDING  
Hello Timer (seconds.................. N/A  
Failover Timer (seconds).............. N/A  
Ringflap Timer (seconds).............. N/A  
Hello Time Remaining (seconds)........ N/A  
Failover Time Remaining (seconds)..... N/A  
Ringflap Time Remaining (seconds)..... N/A  
Hello Sequence........................ N/A  
Data Vlans............................ 2  
-------------------------------------------------------------------------------  
Classifiers and Hardware Filters  
On AT-8948, AT-9900, AT-9900s, and x900 series switches, the switching hardware has a limit  
of 16 bytes to use for matching on incoming packets.  
EPSR creates a hardware filter that uses 2 bytes for VLAN identification (since version  
29 -04). This means that you have to design your network carefully when using EPSR with  
1
DHCP snooping, QoS, or other hardware filters.  
For example:  
•
•
DHCP snooping uses 5 bytes to match on the source and destination UDP ports and the  
protocol field. With EPSR and DHCP snooping both enabled, 7 out of the  
used.  
16 bytes are  
IP addresses use 4 bytes. So if you configured EPSR, DHCP snooping, and a QoS policy  
that classified on source IP address, then 11 of the 6 bytes would be used.  
1
Page 29 | AlliedWare™ OS How To Note: EPSR  
 
 
Ports and Recovery Times  
Ports and Recovery Times  
In practice, recovery time in an EPSR ring is generally between 50 and 100ms. However, it  
depends on the port type, because this determines how long it takes for the port to report  
that it is down and send a Link-Down message.  
The following ports report that they are down immediately or within a few milliseconds,  
which leads to an EPSR recovery time of 50 to 100ms:  
•
•
•
•
1
0/  
tri-speed copper RJ-45 ports operating at  
fiber 000M ports  
0G ports  
100M copper RJ-45 ports  
10 or 100M  
1
1
However, for tri-speed copper RJ-45 ports operating at  
either 350ms or 750ms—before the port reports that it is down. This is because the IEEE  
standard for 000BASE-T specifies that a port must wait for a certain length of time after a  
link goes down before it decides that the link is actually down (see Section 40.4.5.2 of  
IEEE Std 802.3-2002). The length of the wait depends on whether the 000BASE-T port is  
“master” or “slave” end of the link (“master” and “slave” are determined when the port  
1000M, there is a short delay—  
1
1
autonegotiates and are not related to the master node of EPSR). If a  
master the wait is 750ms; if it is the slave, the wait is 350ms.  
1
000BASE-T port is the  
This means that if a 1000M copper  
link goes down between two  
transit nodes, EPSR recovers after  
approximately 350ms. The EPSR  
nodes at both ends of the broken  
link send a Link-Down message  
when they detect that the link has  
gone down. As the diagram shows,  
the node at the slave end of the  
link sends a Link-Down message in  
350ms. The node at the master  
end does not send a Link-Down  
message until 750ms have passed,  
but by then the EPSR master node  
has already handled the first Link-  
Down message. You can see the  
messages in the debugging output  
in "Link Down Between Two  
Master  
Node  
Link-Down  
1
after 350ms  
Transit  
Node  
Transit  
Node  
slave end  
of link  
Transit  
Node  
Link-Down  
after 750ms  
2
master end  
of link  
epsr-copper  
Transit Nodes" on page 47.  
For almost all networks, this slight delay in recovery has no practical effect. For networks  
with extremely stringent failover requirements, we recommend using fiber  
instead of copper.  
1000M ports  
Page 30 | AlliedWare™ OS How To Note: EPSR  
 
 
IGMP Snooping and Recovery Times  
IGMP Snooping and Recovery Times  
Since Software Version 281-03, IGMP snooping includes query solicitation, a new feature  
that minimises loss of multicast data after a topology change.  
When IGMP snooping is enabled on a VLAN, and EPSR changes the underlying link layer  
topology of that VLAN, this can interrupt multicast data flow for a significant length of time.  
Query solicitation prevents this by monitoring the VLAN for any topology changes. When it  
detects a change, it generates a special IGMP Leave message known as a Query Solicit, and  
floods the Query Solicit message to all ports. When the IGMP Querier receives the message,  
it responds by sending a General Query. This refreshes snooped group membership  
information in the network.  
Query solicitation functions by default (without you enabling it) on the EPSR master node. By  
default, the master node always sends a Query Solicit message when the topology changes.  
On other switches in the network, the query solicitation is disabled by default, but you can  
enable it by using the command:  
set igmpsnooping vlan={vlan-name|1..4094|all}  
querysolicit={on|yes|true}  
If you enable query solicitation on an EPSR transit node, both that node and the master node  
send a Query Solicit message.  
Once the Querier receives the Query Solicit message, it sends out a General Query and  
waits for responses, which update the snooping information throughout the network. If  
necessary, you can reduce the time this takes by tuning the IGMP timers, especially the  
queryresponseinterval parameter. For more information, see the “IGMP Timers and  
Counters” section of “How To Configure IGMP on Allied Telesyn Routers and Switches for  
Multicasting”. This How To Note is available in the Resource Center of the Documentation  
and Tools CDROM for Software Version 2.8.1, or from:  
www.alliedtelesyn.co.uk/en-gb/solutions/techdocs.asp?area=howto  
Query solicitation also works with networks that use Spanning Tree (STP, RSTP, or MSTP).  
Health Message Priority  
EPSR uses Health messages to check that the ring is intact. If switches in the ring were to  
drop Health messages, this could make the ring unstable. Therefore, Health messages are  
sent to the highest priority queue (queue 7), which uses strict priority scheduling by default.  
This makes sure that the switches forward Health messages even if the network is congested.  
We recommend that you leave queue 7 as the highest priority queue, leave it using strict  
priority scheduling, and only send essential control traffic to it.  
In the unlikely event that this is impossible, you can increase the failover time so that the  
master node only changes the ring topology if several Health messages in a row fail to arrive.  
By default, the failover time is set to two seconds, which means that the master node decides  
that the ring is down if two Health messages in a row fail to arrive.  
Page 31 | AlliedWare™ OS How To Note: EPSR  
 
   
EPSR State and Settings  
EPSR State and Settings  
To display the EPSR state, the attached VLANs, the ring ports, and the timer values, use the  
command:  
show epsr  
Master Node The following diagram shows the output for a master node in a ring that is in a state of  
in a Complete  
Ring  
Complete. As well as giving the state as Complete, it also shows that port  
port and port 2 is the secondary port. Note that the secondary port is blocked, so does not  
1
is the primary  
forward packets over the data VLAN (vlan2).  
EPSR Information  
------------------------------------------------------------------------  
Name ........................ test  
Mode .......................... Master  
Status ........................ Enabled  
State ......................... Complete  
Control Vlan .................. vlan1000 (1000)  
Data VLAN(s) .................. vlan2 (2)  
Primary Port .................. 1  
Primary Port Status ........... Forwarding  
Secondary Port ................ 2  
Secondary Port Status ......... Blocked  
Hello Time .................... 1 s  
Failover Time ................. 2 s  
Ring Flap Time ................ 0 s  
Trap .......................... Enabled  
------------------------------------------------------------------------  
Transit Node The following diagram shows the output for a transit node in a ring that is in a state of  
in a Complete  
Ring  
Complete. Note that the State is Links-Up, not Complete. Only the master node shows  
Complete as the state.  
EPSR Information  
------------------------------------------------------------------------  
Name ........................ test  
Mode .......................... Transit  
Status ........................ Enabled  
State ......................... Links-Up  
Control Vlan .................. vlan1000 (1000)  
Data VLAN(s) .................. vlan2 (2)  
First Port .................... 1  
First Port Status ............. Forwarding  
First Port Direction .......... Upstream  
Second Port ................... 2  
Second Port Status ............ Forwarding  
Second Port Direction ......... Downstream  
Trap .......................... Enabled  
Master Node ................... 00-00-cd-28-06-19  
------------------------------------------------------------------------  
Page 32 | AlliedWare™ OS How To Note: EPSR  
 
 
EPSR State and Settings  
Master Node In contrast, the following diagram shows the output for a master node in a ring that is in a  
in a Failed Ring  
Failed state. Both ring ports are now forwarding.  
EPSR Information  
------------------------------------------------------------------------  
Name ........................ domain1  
Mode .......................... Master  
Status ........................ Enabled  
State ......................... Failed  
Control Vlan .................. vlan1000 (1000)  
Data VLAN(s) .................. vlan2 (2)  
Primary Port .................. 1  
Primary Port Status ........... Forwarding  
Secondary Port ................ 2  
Secondary Port Status ......... Forwarding  
Hello Time .................... 1 s  
Failover Time ................. 2 s  
Ring Flap Time ................ 0 s  
Trap .......................... Enabled  
------------------------------------------------------------------------  
Page 33 | AlliedWare™ OS How To Note: EPSR  
 
SNMP Traps  
SNMP Traps  
You can use SNMP traps to notify you when events occur in the EPSR ring.  
Download the latest version of the Allied Telesis Enterprise MIB from  
www.alliedtelesis.co.nz/support/updates/patches.html. The EPSR Group is contained in the  
sub-file called atr-epsr.mib.  
The EPSR Group has the object identifier prefix epsr ({ modules  
collection of objects and traps for monitoring EPSR states.  
136}), and contains a  
The following trap is defined under the epsrEvents ({ epsr 0}) subtree:  
atrEpsrNodeTrap ({ epsrEvents }) is the trap type of the EPSR node trap (master/transit).  
•
1
The following objects are defined under the epsrEventVariables ({ epsr  
1}) subtree:  
•
atrEpsrNodeTrapType ({epsrEventVariables  
(master/transit).  
1}) is the trap type of the EPSR node trap  
•
•
atrEpsrDomainName ({epsrEventVariables 2}) is the name assigned to the EPSR domain.  
atrEpsrFromState ({epsrEventVariables 3}) is the defined state that an EPSR domain is  
transitioning from.  
•
•
atrEpsrToState ({epsrEventVariables 4}) is the state that an EPSR domain is transitioning  
to.  
atrEpsrControlVLANId ({epsrEventVariables 5}) is the VLAN identifier for the control  
VLAN.  
•
•
atrEpsrPrimaryIfIndex ({epsrEventVariables 6}) is the ifIndex of the primary interface.  
atrEpsrPrimaryIfState ({epsrEventVariables 7}) is the current state of the primary  
interface.  
•
•
atrEpsrSecondaryIfIndex ({epsrEventVariables 8}) is the ifIndex of the secondary  
interface.  
atrEpsrSecondaryIfState ({epsrEventVariables 9}) is the current state of the secondary  
interface.  
Page 34 | AlliedWare™ OS How To Note: EPSR  
 
 
Counters  
Counters  
The EPSR counters record the number of EPSR messages that the CPU received and  
transmitted. To display the counters, use the command:  
show epsr=domain1 count  
Master node in The following diagram shows the counters for a master node in a ring that has never had a  
a Complete  
ring  
link or node fail.  
EPSR Counters  
------------------------------------------------------------------------  
Name: domain1  
Receive:  
Total EPSR Packets  
Health  
Transmit:  
Total EPSR Packets  
Health  
1093  
1092  
1093  
1092  
Ring Up  
Ring Down  
Link Down  
Invalid EPSR Packets  
1
0
0
0
Ring Up  
Ring Down  
Link Down  
1
0
0
------------------------------------------------------------------------  
Note that the node has generated 1093 EPSR packets (and sent them out its primary port)  
and has received the same number of EPSR packets (on its secondary port).  
However, it is very common to see a few Link Down, Ring Down, and Ring Up entries in the  
output of a ring that has never been in a Failed state. These messages are produced when you  
first enable EPSR, if some ring nodes establish before others.  
Transit Node In contrast, the following diagram shows the counters for a transit node in a ring that has  
in a ring that  
had failures  
been in a Failed state twice.  
EPSR Counters  
------------------------------------------------------------------------  
Name: domain1  
Receive:  
Total EPSR Packets  
Health  
Transmit:  
Total EPSR Packets  
Health  
1425  
1423  
2
0
0
0
2
Ring Up  
Ring Down  
Link Down  
Invalid EPSR Packets  
2
0
0
0
Ring Up  
Ring Down  
Link Down  
------------------------------------------------------------------------  
Here, the transit node has received 1421 Health messages, which it will have forwarded on if  
its ports were up. These messages do not show in the transmit counters because they are  
transmitted by the switching hardware, not the CPU.  
The node has also generated two Link-Down messages, indicating that on two separate  
occasions one of its links has gone down.  
Page 35 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
Debugging  
This section walks you through the EPSR debugging output as links go down and come back  
up again. The debugging output comes from the ring in "Example : A Basic Ring" on page 11.  
The output shows what happened when we took down two separate links in turn:  
1
•
•
first, the link between the master node’s primary port and transit node B  
second, the link between the two transit nodes B and C  
To enable debugging on the domain called “test”, use the command:  
enable epsr=test debug=all  
Note that the master node transmits Health messages every second by default. The  
debugging displays every message, including all Health messages. Therefore, we recommend  
that you capture the debugging output for separate analysis, to make analysis simpler.  
Link Down Between Master Node and Transit Node  
This section shows the debugging output when the link between the master node’s primary  
port and transit node B goes down and comes back up again. It shows the debugging output  
for the complete failure and recovery cycle:  
•
•
first on the master node  
then on transit node B.  
Master Node (Node A) Debug Output  
The following debugging output starts with the ring established and in a state of Complete.  
1. The master node sends Health messages  
Each time the Hello timer expires, the master node sends a Health message out its primary  
port (port 1). As long as the ring is in a state of Complete, it receives each Health message  
again on its secondary port (port 2). Note that in the System field, this output shows the  
MAC address of the source of the message—the master node in this case.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541f2a 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000be  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 190  
-----------------------------------------------------------------------  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541f2a 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000be  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 190  
-----------------------------------------------------------------------  
Page 36 | AlliedWare™ OS How To Note: EPSR  
 
       
Debugging  
2. The master node continues sending Health messages  
The master node continues sending Health messages, and increments the Hello Sequence  
number with each message. If all nodes and links in the ring are intact, these Health messages  
are the only debugging output you see.  
.
.
.
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eef 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000f9  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 249  
-----------------------------------------------------------------------  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eef 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000f9  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 249  
-----------------------------------------------------------------------  
3. The primary port goes down  
The link between the master node’s primary port and the neighbouring transit node goes  
down. Therefore, the master node detects that its primary port (port 1) has gone down.  
EPSR test, Port 1 port down  
Flush FDB EPSR: test vid: 2  
Page 37 | AlliedWare™ OS How To Note: EPSR  
 
Debugging  
4. The master node receives a Link-Down message on its secondary port  
The master node receives a Link-Down message on its secondary port (port 2) from transit  
node B, which is at the other end of the broken link.  
EPSR Port2 Rx: 00e02b00 00040000 cd24024f 8100e3e8 005caaaa 0300e02b  
00bb0100 00542484 00000000 0000cd24 024f990b 00400108 03e80000  
00000000 cd24024f 00000000 04000000  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = LINK-DOWN  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = LINK-DOWN  
SYSTEM = 00-00-cd-24-02-4f  
FAIL TIME = 0  
-----------------------------------------------------------------------  
In the System field, this output shows the MAC address of the source of the message—the  
transit node in this case.  
5. The master node transmits a Ring-Down-Flush-FDB message  
The master switch responds to the break in the ring by sending a Ring-Down-Flush-FDB  
message, which tells each transit node to learn the new topology. The master node also  
unblocks its secondary port for the data VLAN (vlan2), flushes its FDB, sends an SNMP trap,  
and changes the EPSR state to Failed. Note that the master node sends the Ring-Down-  
Flush-FDB message only out its secondary port, because the link between the primary port  
and the neighbouring transit node is down.  
EPSR Port2 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ee9 00000000 0000cd28 0619990b 00400107 03e80000  
00000000 cd280619 00000000 02000000  
EPSR Port2 Tx:  
-----------------------------------------------------------------------  
TYPE = RING-DOWN-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Unblock EPSR:test port:2 VLAN:2  
Flush FDB EPSR: test vid: 2  
EPSR INFO: Send trap EPSR:test oldState:COMPLETE newState:FAILED  
nodeType:MASTER  
EPSR test oldState:COMPLETE newState:FAILED  
Page 38 | AlliedWare™ OS How To Note: EPSR  
 
   
Debugging  
6. The Hello timer expires  
The Hello timer expires, which would normally trigger the master node to send a Health  
message out the primary port. However, the link between the primary port and the  
neighbouring transit node is down, so the master node does not send the Health message.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
7. The primary port comes back up  
The primary port comes back up. The master node immediately blocks that port for vlan2 to  
prevent a loop.  
Manager x900-48-A>  
EPSR test, Port 1 port up  
Block EPSR:test port:1 VLAN:2  
8. The Hello timer expires again  
The Hello timer expires again. Port  
1
is now up, so this time the master node sends a Health  
message. The Health message shows that the EPSR state is Failed.  
Note that the hello sequence number increments from the number it was before the primary  
port went down, because the master node could not transmit Health messages while the  
port was down.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541dee 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 020000fa  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 250  
-----------------------------------------------------------------------  
Page 39 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
9. The master node receives the Health message on its secondary port  
The master node receives the Health message on its secondary port (port 2). This tells it  
that all links on the ring are up again.  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541dee 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 020000fa  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 250  
----------------------------------------------------------------------  
10. The master node returns the ring to a state of Complete  
The master node blocks its secondary port for the data VLAN, unblocks its primary port,  
transmits a Ring-Up-Flush-FDB message, flushes its FDB, sends a trap, and changes the EPSR  
state to Complete.  
Block EPSR:test port:2 VLAN:2  
Unblock EPSR:test port:1 VLAN:2  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541fea 00000000 0000cd28 0619990b 00400106 03e80000  
00000000 cd280619 00000000 01000000  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = RING-UP-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Flush FDB EPSR: test vid: 2  
EPSR INFO: Send trap EPSR:test oldState:FAILED newState:COMPLETE  
nodeType:MASTER  
EPSR test oldState:FAILED newState:COMPLETE  
11. The master node receives the Ring-Up-Flush-FDB message on port 2  
The master node receives the Ring-Up-Flush-FDB message back on its secondary port,  
because the packet traversed the whole ring. The master node ignores the message.  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541fea 00000000 0000cd28 0619990b 00400106 03e80000  
00000000 cd280619 00000000 01000000  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = RING-UP-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Page 40 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
12. The master node transmits and receives Health messages  
The master node continues transmitting and receiving Health messages for as long as the ring  
stays in a state of Complete.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eed 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000fb  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 251  
-----------------------------------------------------------------------  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eed 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000fb  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 251  
-----------------------------------------------------------------------  
.
.
.
Page 41 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
Transit Node (Node B) Debug Output  
The following debugging shows the same events as the previous section, but on the transit  
node instead of the master node. It starts with the ring established and in a state of  
Complete.  
1. The transit node receives Health messages  
The transit node receives Health messages on port 1, because that port is connected to the  
master node’s primary port. Note that in the System field, this output shows the MAC  
address of the source of the message—the master node in this case.  
This is the packet shown in step 1 on page 36 of the master node debug output.  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541f2a 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000be  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 190  
-----------------------------------------------------------------------  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541f29 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000bf  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 191  
-----------------------------------------------------------------------  
.
.
.
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eef 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000f9  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 249  
-----------------------------------------------------------------------  
Page 42 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
2. Port  
1
on the transit node goes down  
The transit node detects that port  
gone down. The transit node flushes its forwarding database, blocks port  
1
(between the transit node and the master node) has  
for the data  
1
VLAN (to prevent a loop from forming when the master node comes back up), sends a Link-  
Down message towards the master node, sends a trap, and changes the EPSR state to Link-  
Down.  
This is the packet shown in step 4 on page 38 of the master node debug output.  
EPSR test, Port 1 port down  
Flush FDB EPSR: test vid: 2  
Block EPSR:test port:1 VLAN:2  
EPSR Port2 Tx: 00e02b00 00040000 cd24024f 8100e3e8 005caaaa 0300e02b  
00bb0100 00542484 00000000 0000cd24 024f990b 00400108 03e80000  
00000000 cd24024f 00000000 04000000  
EPSR Port2 Tx:  
-----------------------------------------------------------------------  
TYPE = LINK-DOWN  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = LINK-DOWN  
SYSTEM = 00-00-cd-24-02-4f  
FAIL TIME = 0  
-----------------------------------------------------------------------  
EPSR INFO: Send trap EPSR:test oldState:LINK-UP newState:LINK-DOWN  
nodeType:TRANSIT  
EPSR test oldState:LINK-UP newState:LINK-DOWN  
3. The transit node receives a Ring-Down-Flush-FDB message.  
In response to the Link-Down message, the master node sends a Ring-Down-Flush-FDB  
message. However, this transit node does not need to flush its database—it already did.  
This is the packet shown in step 5 on page 38 of the master node debug output.  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ee9 00000000 0000cd28 0619990b 00400107 03e80000  
00000000 cd280619 00000000 02000000  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = RING-DOWN-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Page 43 | AlliedWare™ OS How To Note: EPSR  
 
Debugging  
4. Port  
1
comes back up  
The transit node detects that port  
1
has come back up. It sends a trap and changes the EPSR  
state to Pre-forwarding. Note that it leaves port  
1
blocked for vlan2, to make sure there are  
no loops.  
Manager 9924-B>  
Block EPSR:test port:1 VLAN:2  
EPSR test, Port 1 port up  
EPSR INFO: Send trap EPSR:test oldState:LINK-DOWN newState:PRE-FORWARDING  
nodeType:TRANSIT  
EPSR test oldState:LINK-DOWN newState:PRE-FORWARDING  
5. Transit node receives a Health message  
Now that the master node’s primary port is up again, it sends a Health message. Now that  
the transit node’s port  
message. This demonstrates that the transit node has only blocked port  
1
is up again for the control VLAN, the transit node receives the  
for the data VLAN,  
1
not the control VLAN. EPSR control messages never loop because the master node never  
forwards them between its ring ports.  
Note that the hello sequence number increments from the number it was before the primary  
port went down, because the master node could not transmit Health messages while the  
port was down.  
This is the packet shown in step 8 on page 39 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541dee 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 020000fa  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 250  
-----------------------------------------------------------------------  
Page 44 | AlliedWare™ OS How To Note: EPSR  
 
Debugging  
6. Transit node receives a Ring-Up-Flush-FDB message.  
The Health message from the previous step reaches the master node and shows it that all  
links in the ring are now up. The master node sends a Ring-Up-Flush-FDB message. When it  
receives the message, the transit node unblocks port  
trap, and changes the state to Link-Up.  
1
for vlan2, flushes its FDB, sends a  
This is the packet shown in step 10 on page 40 of the master node debug output.  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541fea 00000000 0000cd28 0619990b 00400106 03e80000  
00000000 cd280619 00000000 01000000  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = RING-UP-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Unblock EPSR:test port:1 VLAN:2  
Flush FDB EPSR: test vid: 2  
EPSR INFO: Send trap EPSR:test oldState:PRE-FORWARDING newState:LINK-UP  
nodeType:TRANSIT  
EPSR test oldState:PRE-FORWARDING newState:LINK-UP  
Page 45 | AlliedWare™ OS How To Note: EPSR  
 
Debugging  
7. The transit node receives Health messages  
The transit node continues receiving Health messages for as long as the ring stays in a state of  
Complete.  
This is the packet shown in step 12 on page 41 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eed 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000fb  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 251  
-----------------------------------------------------------------------  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541eec 00000000 0000cd28 0619990b 00400105 03e80000  
00000000 cd280619 00010002 010000fc  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 252  
-----------------------------------------------------------------------  
.
.
.
Page 46 | AlliedWare™ OS How To Note: EPSR  
 
Debugging  
Link Down Between Two Transit Nodes  
This section shows the debugging output when the link between transit node B and transit  
node C goes down and comes back up again. It shows the debugging output for the complete  
failure and recovery cycle:  
•
•
on the master node, and then  
on transit node B  
Master Node (Node A) Debug Output  
The following debugging output starts with the ring established and in a state of Complete.  
1. The master node sends Health messages  
Each time the Hello timer expires, the master node sends a Health message out its primary  
port (port 1). As long as the ring is in a state of Complete, it receives each Health message  
again on its secondary port (port 2).  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ea1 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000147  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 327  
-----------------------------------------------------------------------  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ea1 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000147  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 327  
-----------------------------------------------------------------------  
Page 47 | AlliedWare™ OS How To Note: EPSR  
 
     
Debugging  
2. The link between the two transit nodes goes down  
When the link goes down, the master node transmits a Health message but does not receive  
it on its secondary port.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ea0 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000148  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 328  
-----------------------------------------------------------------------  
3. The master node receives a Link-Down message on its secondary port  
The master node receives a Link-Down message, which tells it that a link in the ring is  
broken. This message came from the transit node on one side of the broken link.  
EPSR Port2 Rx: 00e02b00 00040000 cd20f101 8100e3e8 005caaaa 0300e02b  
00bb0100 00544726 00000000 0000cd20 f101990b 00400108 03e80000 00000000  
cd20f101 00000000 04000000  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = LINK-DOWN  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = LINK-DOWN  
SYSTEM = 00-00-cd-20-f1-01  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Page 48 | AlliedWare™ OS How To Note: EPSR  
 
   
Debugging  
4. The master node transmits a Ring-Down-Flush-FDB message  
In response to the Link-Down message, the master node transmits a Ring-Down-Flush-FDB  
message out both its primary and secondary ports. The message has to go out both ports to  
make sure it reaches the nodes on both sides of the broken link. The master node also  
unblocks its secondary port for vlan2, flushes its forwarding database, sends a trap, and  
changes the EPSR state to Failed.  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ee9 00000000 0000cd28 0619990b 00400107 03e80000 00000000  
cd280619 00000000 02000000  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = RING-DOWN-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
EPSR Port2 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ee9 00000000 0000cd28 0619990b 00400107 03e80000 00000000  
cd280619 00000000 02000000  
EPSR Port2 Tx:  
-----------------------------------------------------------------------  
TYPE = RING-DOWN-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Unblock EPSR:test port:2 VLAN:2  
Flush FDB EPSR: test vid: 2  
EPSR INFO: Send trap EPSR:test oldState:COMPLETE newState:FAILED  
nodeType:MASTER  
EPSR test oldState:COMPLETE newState:FAILED  
5. The master node receives a second Link-Down message  
The master node receives a Link-Down message from the transit node on the other side of  
the broken link. This message arrived after a delay because the ring ports are 1000M ports  
(see "Ports and Recovery Times" on page 30). The master node does not take any action in  
response to this message, because it already responded to the broken link.  
Manager x900-48-A>  
EPSR Port1 Rx: 00e02b00 00040000 cd24024f 8100e3e8 005caaaa 0300e02b  
00bb0100 00542484 00000000 0000cd24 024f990b 00400108 03e80000 00000000  
cd24024f 00000000 04000000  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = LINK-DOWN  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = LINK-DOWN  
SYSTEM = 00-00-cd-24-02-4f  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Page 49 | AlliedWare™ OS How To Note: EPSR  
 
   
Debugging  
6. The master node continues sending Health messages  
The master node continues sending Health messages out its primary port. It does not receive  
any of these at the secondary port, which tells it that the link is still down.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541d9f 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 02000149  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 329  
-----------------------------------------------------------------------  
.
.
.
7. The master node receives a Health message  
The master node transmits a Health message and receives it at the secondary port. This  
indicates that the link is back up.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541d72 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 02000176  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 374  
-----------------------------------------------------------------------  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541d72 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 02000176  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 374  
-----------------------------------------------------------------------  
Page 50 | AlliedWare™ OS How To Note: EPSR  
 
   
Debugging  
8. The master node returns the ring to a state of Complete  
Now that the ring is back up, the master node blocks its secondary port for the data VLAN,  
transmits a Ring-Up-Flush-FDB message, flushes its FDB, sends a trap, and changes the EPSR  
state to Complete.  
Block EPSR:test port:2 VLAN:2  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541fea 00000000 0000cd28 0619990b 00400106 03e80000 00000000  
cd280619 00000000 01000000  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = RING-UP-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Flush FDB EPSR: test vid: 2  
EPSR INFO: Send trap EPSR:test oldState:FAILED newState:COMPLETE  
nodeType:MASTER  
EPSR test oldState:FAILED newState:COMPLETE  
9. The master node receives the Ring-Up-Flush-FDB message on port 2  
The master node receives the Ring-Up-Flush-FDB message back on its secondary port,  
because the packet traversed the whole ring. The master node ignores the message.  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541fea 00000000 0000cd28 0619990b 00400106 03e80000 00000000  
cd280619 00000000 01000000  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = RING-UP-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Page 51 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
10. The master node transmits and receives Health messages  
The master node continues transmitting and receiving Health messages for as long as the ring  
stays in a state of Complete.  
Manager x900-48-A>  
epsrHelloTimeout: EPSR test Hello Timer expired  
EPSR Port1 Tx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541e71 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000177  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 375  
-----------------------------------------------------------------------  
EPSR Port2 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541e71 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000177  
EPSR Port2 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 375  
-----------------------------------------------------------------------  
.
.
.
Page 52 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
Transit Node (Node B) Debug Output  
The following debugging shows the same events as the previous section, but on the transit  
node instead of the master node. It starts with the ring established and in a state of  
Complete.  
1. The transit node receives Health messages  
The transit node receives Health messages on port 1, because that port is connected to the  
master node’s primary port. Note that the message shows that the ring state is Complete.  
This is the packet shown in step 1 on page 47 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ea1 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000147  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 327  
-----------------------------------------------------------------------  
.
.
.
2. The link between the two transit nodes goes down  
The transit node receives Health message 328. At this stage, the message does not indicate  
that anything is wrong. However, between messages 327 and 328, the link went down. This  
means that message 328 will not make it back to the master node.  
This is the packet shown in step 2 on page 48 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ea0 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000148  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 328  
-----------------------------------------------------------------------  
Page 53 | AlliedWare™ OS How To Note: EPSR  
 
 
Debugging  
3. The transit node receives a Ring-Down-Flush-FDB message  
In the meanwhile, the master node has received a Link-Down message from the switch at the  
other end of the broken link (in step 3 on page 48). Therefore, the master node realises that  
the ring is broken and acts accordingly. As part of the recovery process, the master node  
sends a Ring-Down-Flush-FDB message. The transit node receives this message and flushes  
its forwarding database.  
This is the packet shown in step 4 on page 49 of the master node debug output.  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541ee9 00000000 0000cd28 0619990b 00400107 03e80000 00000000  
cd280619 00000000 02000000  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = RING-DOWN-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Flush FDB EPSR: test vid: 2  
4. The transit node sends a Link-Down message  
The transit node realises that its port is down, sends a Link-Down message, sends a trap, and  
changes its state to Link-Down. The transit node sends this message some time after the link  
actually went down, because the ring ports are 1000M ports (see "Ports and Recovery  
Times" on page 30). Note that by this stage the ring has already changed topology to restore  
traffic flow. The master node detected the link failure by receiving a Link-Down message  
from the other side of the link.  
This is the Link-Down message that the master switch received in step 5 on page 49.  
Manager 9924-B>  
EPSR test, Port 2 port down  
Flush FDB EPSR: test vid: 2  
Block EPSR:test port:2 VLAN:2  
EPSR Port1 Tx: 00e02b00 00040000 cd24024f 8100e3e8 005caaaa 0300e02b  
00bb0100 00542484 00000000 0000cd24 024f990b 00400108 03e80000 00000000  
cd24024f 00000000 04000000  
EPSR Port1 Tx:  
-----------------------------------------------------------------------  
TYPE = LINK-DOWN  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = LINK-DOWN  
SYSTEM = 00-00-cd-24-02-4f  
FAIL TIME = 0  
-----------------------------------------------------------------------  
EPSR INFO: Send trap EPSR:test oldState:LINK-UP newState:LINK-DOWN  
nodeType:TRANSIT  
EPSR test oldState:LINK-UP newState:LINK-DOWN  
Page 54 | AlliedWare™ OS How To Note: EPSR  
 
Debugging  
5. The transit node receives Health messages  
The transit node receives Health messages from the master node. These have a state of  
Failed, which shows that the ring is still broken.  
This is the packet shown in step 6 on page 50 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541d9f 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 02000149  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 329  
-----------------------------------------------------------------------  
.
.
.
6. The link comes back up  
The transit node detects that the broken link has come back up. It blocks the port to prevent  
a loop from occurring, sends a trap, and changes the EPSR state to Pre-forwarding.  
Manager 9924-B>  
Block EPSR:test port:2 VLAN:2  
EPSR test, Port 2 port up  
EPSR INFO: Send trap EPSR:test oldState:LINK-DOWN newState:PRE-FORWARDING  
nodeType:TRANSIT  
EPSR test oldState:LINK-DOWN newState:PRE-FORWARDING  
7. The transit node receives another Health message  
The transit node receives another Health message. This message will make it back to the  
master node’s secondary port, because the link between the two transit nodes is now up.  
This is the packet shown in step 7 on page 50 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541d72 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 02000176  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = FAILED  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 374  
-----------------------------------------------------------------------  
Page 55 | AlliedWare™ OS How To Note: EPSR  
 
8. The transit node receives a Ring-Up-Flush-FDB message  
The transit node receives a Ring-Up-Flush-FDB message, which indicates that the master  
node knows that all links in the ring are up again. The transit node unblocks port 2 for vlan2,  
flushes its FDB, sends a trap, and changes state to Link-Up.  
This is the packet shown in step 8 on page 51 of the master node debug output.  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541fea 00000000 0000cd28 0619990b 00400106 03e80000 00000000  
cd280619 00000000 01000000  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = RING-UP-FLUSH-FDB  
CTRL VLAN = 1000  
HELLO TIME = 0  
HELLO SEQ = 0  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 0  
-----------------------------------------------------------------------  
Unblock EPSR:test port:2 VLAN:2  
Flush FDB EPSR: test vid: 2  
EPSR INFO: Send trap EPSR:test oldState:PRE-FORWARDING newState:LINK-UP  
nodeType:TRANSIT  
EPSR test oldState:PRE-FORWARDING newState:LINK-UP  
9. The transit node receives Health messages  
The transit node continues receiving Health messages for as long as the ring stays in a state of  
Complete.  
This is the packet shown in step 10 on page 52 of the master node debug output.  
Manager 9924-B>  
EPSR Port1 Rx: 00e02b00 00040000 cd280619 8100e3e8 005caaaa 0300e02b  
00bb0100 00541e71 00000000 0000cd28 0619990b 00400105 03e80000 00000000  
cd280619 00010002 01000177  
EPSR Port1 Rx:  
-----------------------------------------------------------------------  
TYPE = HEALTH  
CTRL VLAN = 1000  
HELLO TIME = 1  
STATE = COMPLETE  
SYSTEM = 00-00-cd-28-06-19  
FAIL TIME = 2  
HELLO SEQ = 375  
----------------------------------------------------------------------  
.
.
.
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www.alliedtelesis.com  
© 2007 AlliedTelesis, Inc. All rights reserved. Information in this document is subject to change without notice. AlliedTelesis is a trademark or registered trademark of AlliedTelesis, Inc. in the United States and other countries.  
All company names, logos, and product designs that are trademarks or registered trademarks are the property of their respective owners.  
C613-16092-00 REV D  
 

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