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[BTI] Example - How to configure SA822/821/805 station loopback

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Summary:

Station loopbacks enable operators to verify the integrity of links across a network. When a station loopback is started on a switch, the switch loops back certain specified traffic based on configured match criteria. All incoming frames that match the criteria for all active station loopback instances are looped back. Frames that match are looped back on the port on which they are received. The switch swaps the MAC DA and SA, and recalculates the CRC before sending the frame back.

In this article, we introduce the steps to configure the two station loopbacks that are supported on the BTI 822/821/805 product.

 

Symptoms:

For BTI SA822/821/805 series, two types of station loopbacks are supported: NNI Ingress Loopback and UNI Egress Loopback.

Both station loopbacks are based on the EVC. The UNI egress loopback requires the C-VLAN ID and loopback point, whereas the NNI ingress loopback requires S-VLAN ID and destination MAC address (optional). Customers can use these two station loopbacks to verify network link connectivity and packet forwarding within the switch.

 

Cause:

Station loopbacks are quite useful for testing circuit throughput and troubleshoot circuit packet loss issues in layer 2 forwarding paths. With both UNI/NNI station loopbacks, customers can easily check network connectivity hop-by-hop and determine any packet loss that may occur in a segment.

 

Solution:

In the following simplified network topology, two SA821 systems are connected via port eth-0-27, which is configured as the NNI port nni27. An epline service called epl01 (svlan-id 1234) has been configured between two nodes with eth-0-2 (1:1:1:GIGE2) configured as the UNI port on both ends. The eservice type for this example is epline, but the configuration applies for E(v)pline and E(v)plan services as well.

Below is the epline service on node 821-Z. The tester is connected to the UNI port eth-0-2 on node 821-A to send traffic, and the station loopback is configured on node 821-Z to verify network connectivity.

 

Station loopback for UNI port

The command that is used to enable the station loopback for the UNI port on node 821-Z at the far end is as follows:

821-Z(config)# station-loopback session stlb01 service-type evc epl01 uni UNI-0-2 cvlan 50:150
821-Z(config)# exit
821-Z# station-loopback session stlb01 start

In the above configuration command, stlb01 is the name of the station loopback session, which can be customized. The station loopback for a UNI interface would need the C-VLAN ID information, which you can customize based on the tester setting. The C-VLAN ID value ranges from 50 to 150, and you can set different VLAN IDs by separating then with a comma, such as c-vlan 2, 3, 7, 8.

To check the station loopback statistics while testing and verify that frames were looped back, use the following:

show station-loopback session stlb01

The above output shows the station loopback sessions status, the applied interface details, and the packets count for packets that were looped back.

After finishing the station loopback test, you would need to stop the station loopback first and delete the station loopback session configuration as follows:

821-Z# station-loopback session stlb01 stop
821-Z# conf t
821-Z(config)#no station-loopback session stlb01
 

Station loopback for NNI port

The command that is used to enable a station loopback for the NNI port on node 821-Z at the far end is as follows:

821-Z(config)# ethernet sat loopback session stlb02 evc epl01 nni nni27 dest-mac 0001.0300.0700
821-Z(config)# exit
821-Z# ethernet sat loopback session stlb02 start

In the above configuration command, stlb02 is the station loopback session name, which can be customized. The station loopback for an NNI interface needs to match the destination MAC address information. Therefore, you would need to customize the destination MAC address based on the tester setting.

To check the station loopback statistics while testing, use the following:

show ethernet sat loopback session stlb02

The above output shows the station loopback sessions status, applied interface details, and packets count of packets that were looped back.

After finishing the station loopback test, stop the station loopback and delete the station loopback configuration by using the following:

821-Z# ethernet sat loopback session stlb02 stop
821-Z# conf t
821-Z(config)#no ethernet sat loopback session stlb02

 

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