Reference Guide

Layer 2 | 529
Important Points about Configuring Redundant Pairs
• You may not configure any interface to be a backup for more than one interface, no interface can have
more than one backup, and a backup interface may not have a backup interface.
• Neither the active nor the backup interface may be a member of a LAG.
• The active and standby do not have to be of the same type (1G, 10G, etc).
• You may not enable any Layer 2 protocol on any interface of a redundant pair or to ports connected to
them.
• STP cannot be used on any interface of a redundant pair or on ports connected to a redundant pair.
• Redundant pairs cannot be used on SONET interfaces.
• All attributes applied to the active port, such as MAC addresses, are also applied to the backup ports.
In Figure 24-8, interface 3/41 is a backup interface for 3/42, and 3/42 is in the down state, as shown in
message Message 1. If 3/41 fails, 3/42 transitions to the up state, which makes the backup link active. A
message similar to Message 1 appears whenever you configure a backup port.
Message 1 Configuring a Backup Layer 2 Port
02:28:04: %RPM0-P:CP %IFMGR-5-L2BKUP_WARN: Do not run any Layer2 protocols on Gi 3/41 and Gi
3/42
02:28:04: %RPM0-P:CP %IFMGR-5-OSTATE_DN: Changed interface state to down: Gi 3/42
02:28:04: %RPM0-P:CP %IFMGR-5-STATE_ACT_STBY: Changed interface state to standby: Gi 3/42