Reference Guide

508 | Layer 2
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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.
• All attributes applied to the active port, such as MAC addresses, are also applied to the backup ports.
In Figure 26-4, 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.
Figure 26-4. CLI for Configuring Redundant Layer 2 Pairs without Spanning Tree
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
FTOS(conf-if-range-gi-3/41-42)#switchport backup interface GigabitEthernet 3/42
FTOS(conf-if-range-gi-3/41-42)#show config
!
interface GigabitEthernet 3/41
no ip address
switchport
switchport backup interface GigabitEthernet 3/42
no shutdown
!
interface GigabitEthernet 3/42
no ip address
switchport
no shutdown
FTOS(conf-if-range-gi-3/41-42)#
FTOS(conf-if-range-gi-3/41-42)#do show ip int brief | find 3/41
GigabitEthernet 3/41 unassigned YES Manual up up
GigabitEthernet 3/42 unassigned NO Manual up down
[output omitted]
FTOS(conf-if-range-gi-3/41-42)#interface gig 3/41
FTOS(conf-if-gi-3/41)#shutdown
00:24:53: %RPM0-P:CP %IFMGR-5-ASTATE_DN: Changed interface Admin state to down: Gi 3/41
FTOS(conf-if-gi-3/41)#00:24:55: %RPM0-P:CP %IFMGR-5-OSTATE_DN: Changed interface state to
down: Gi 3/41
00:24:55: %RPM0-P:CP %IFMGR-5-INACTIVE: Changed Vlan interface state to inactive: Vl 1
00:24:55: %RPM0-P:CP %IFMGR-5-OSTATE_UP: Changed interface state to up: Gi 3/42
00:24:55: %RPM0-P:CP %IFMGR-5-ACTIVE: Changed Vlan interface state to active: Vl 1
00:24:55: %RPM0-P:CP %IFMGR-5-STATE_STBY_ACT: Changed interface state from standby to active:
Gi 3/42
FTOS(conf-if-gi-3/41)#do show ip int brief | find 3/41
GigabitEthernet 3/41 unassigned NO Manual administratively down down
GigabitEthernet 3/42 unassigned YES Manual up up
[output omitted]