Problem Description

The current network utilizes the EGT2 single board, configured for EPL service, connected to a network of digital pass-through switches, loop detection is required throughout the network, and STP protocol is enabled on the switch devices.

After replacing EGT2 with EGS4, the switch has loop alarms and the service is affected.

Alarm information

None

Processing

Option 1:

Replace the EGT2 single board with a single board that does not support the STP and RSTP protocols.

Option 2:

Replace the EGT2 with an EGS4 single board to de-enable the ingress detection of the EGS4 port.

From the table below, we can see that when port detection is not enabled, STP and RSTP protocol messages are transmitted, which is exactly what we require.

Option 2 is used in this case.

Root Cause

The functions and features of EGT2 single board can be seen:

Provides 2-wayGE transparent transmission, supports EPL, supports transparent transmission of VLANs, and does not support STP and RSTP protocols. In short, all the data messages passing through the EGT2 single board, the EGT2 single board does not do any processing, transparent transmission, this problem we are concerned about the regeneration tree protocol messages are also transparent transmission without any processing.

The functions and characteristics of the EGS4 single board can be seen:

Provides access and processing of 4-wayGE services. It supports transparent transmission of EPL services based on PORT, VLAN and QinQ, adding, deleting and exchanging of VLAN tags, and STP and RSTP protocols. In short, the data passing through the single board of EGS4 can support the transparent transmission of the created EPL service, but because the single board supports STP and RSTP protocols, the STP and RSTP protocol messages passing through the single board will be detected and processed accordingly. In this problem, because the STP and RSTP protocols are not enabled on the EGS4 board in the current network, when the external port receives STP and RSTP protocol messages, they are processed as business messages without transmitting LACP messages, and because the STP and RSTP protocol message format is different from the ordinary business message format, they are eventually discarded. As a result, the remote switch and router cannot receive STP and RSTP protocol messages, and there is a loopback situation on the physical link, which will not activate the Spanning Tree Protocol, and it will cause the loopback of the service.

Lab EGT2 replaced with EGS4 verified results work: OSN3500 and OSN2500 base on version 5.36.18.50.

Recommendations and Summary

Before replacing a single board, check the functions and features of the board and the version of the board.

For example, the replacement of EGT2 by EGS4 in this case causes the switch to have loop alarms. In addition, if the service is with VLAN and the TAG attribute of the EGS4 port is set incorrectly, it may cause the service to be unavailable.

The mismatch between the single board version and the host version of the device may cause false alarms, offline single boards and many other situations.