[All About Switches] Traffic Forwarding Fails on an ERPS Ring

Created Mar 09, 2018 09:26:17Latest reply Mar 09, 2018 13:52:56 1133 1 0 0

Involved Products and Versions

All products and versions

Networking

As shown in Figure 1-1, SwitchA to SwitchD form a ring network on which ERPS is deployed. The interface GE0/0/28 on SwitchA is the RPL owner, which is blocked on the ring. SwitchA and SwitchB are connected to a bypass device.

Figure 1-1 Networking diagram for the traffic forwarding failure on an ERPS ring

20180309092611658001.png

 

Fault Symptom

When the link between SwitchA and SwitchB fails, a loop occurs on the ERPS ring.

Cause Analysis

1.       Only two interfaces on a device can be added to an ERPS ring. Interfaces on both ends of the bypass device on the live network cannot be added to the ERPS ring. The bypass link is not on the ERPS ring and is not protected by ERPS.

2.       When the link between SwitchA and SwitchB fails, they detect the link fault on the ERPS ring and send SF RAPS packets to their two respective ends on the ERPS ring.

3.       After receiving the SF RAPS packets, the blocked interface GE0/0/28 unblocks the blocked link.

4.       After the blocked interface GE0/0/28 is unblocked, traffic is transmitted through the bypass device because the bypass link has no blocking point. As a result, a loop occurs on the entire ERPS ring, affecting all services.

Troubleshooting Procedure

                          Step 1     Remove the connected bypass device. The fault is rectified.

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WoodWood  Admin   Created Mar 09, 2018 13:52:56 Helpful(0) Helpful(0)

thanks
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