Phenomenon Description

The SSND00EGT2 single board is used in the XXX network to configure EPL services and is connected to the Digitizer Switch network, and loop detection is required throughout the network. The digital switch enables the STP protocol to avoid network loops. When the EGS4 single board is used to replace the EGT2, the switch generates a loopback alarm, and services are affected as a result.

Cause Analysis

The SSN3EGT2 single board provides 2-channelGE transparent transmission and does not support STP and RSTP protocols. All data messages (including STP protocol messages) passing through the EGT2 single board are not processed by the EGT2 single board and are transparently transmitted.

SSN1EGS4 single board provides the function of accessing and processing 4-channelGE services and supports STP and RSTP protocols. Transparent transmission of data messages passing through the EGS4 single board can support the creation of EPL services, but because the single board supports STP and RSTP protocols, STP and RSTP protocol messages passing through the single board are detected and processed as service messages.

Since the format of STP and RSTP protocol messages is different from the format of ordinary service messages, they are eventually discarded. Therefore, when the remote switch does not receive STP and RSTP protocol messages and there is a loopback situation on the physical link, the Spanning Tree Protocol cannot take effect, resulting in the loopback of services.

Procedure

De-enable ingress detection on SSN1EGS4 ports so that STP and RSTP protocol messages will not be detected and eventually discarded.

Recommendation Summary

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

The OSN2500SSN1EGS4 in this case replaces EGT2, causing the switch to have a loopback alarm. In addition, if the service is with VLAN and the TAG attribute of the EGS4 port is not set correctly, it may cause the service to be unavailable.

When the single board version does not match the device host version, it may cause false alarms, offline single boards, and many other situations.