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Configuring Redundant Pairs
Configuring Redundant Pairs is supported:
• On physical interfaces on platforms
c e s
• On static and dynamic port-channel interfaces on platforms c e s
The Redundant Pairs feature allows you to provide redundancy for Layer 2 links without using Spanning
Tree (STP). You create redundant links by configuring pairs of Layer 2 (physical or port-channel)
interfaces so that only one interface is up and carries user traffic at any time. Interfaces on either side of a
link provide backup for the primary link. Redundant pairs are useful in service-provider and enterprise
networks in which you do not run STP on switches—for example, networks with Digital Subscriber Line
Access Mutiplexers (DSLAM)—to avoid creating switching loops (see Figure 25-7).
Figure 25-7. Configuring Redundant Layer 2 Pairs without Spanning Tree
You configure a redundant pair by assigning a backup interface to a primary interface with the switchport
backup interface
command. Initially, the primary interface is active and transmits traffic and the backup
interface remains down. If the primary fails for any reason, the backup transitions to an active UP state. If
the primary interface fails and later comes back up, it remains as the backup interface for the redundant
pair.
FTOS supports only Gigabit and 10-Gigabit ports and port channels as primary/backup interfaces in
redundant pairs. (A port channel is also referred to as a Link Aggregation Group (LAG). See Port Channel
Interfaces on page 428 for more information.)
In a redundant pair, any combination of physical and port-channel interfaces is supported as the two
interfaces in a redundant pair. For example, you can configure a static (without LACP) or dynamic (with
LACP) port-channel interface as either the primary or backup link in a redundant pair with a Gigabit
interface.
Note: For details on STP, see Chapter 52, “Spanning Tree Protocol,” on page 1049.
Redundant links create a switching loop.
Without STP broadcast storms occurs.
Force10(conf-if-gi-4/32)#switchport
Force10(conf-if-gi-4/32)#no shutdown
fnC0067mp
Force10(conf-if-gi-3/42)#switchport
Force10(conf-if-gi-3/42)#no shutdown
Backup Link
Use backup interfaces to create redundant
links in networks without STP
Force10(conf-if-gi-4/31)#switchport
Force10(conf-if-gi-4/31)#no shutdown
Force10(conf-if-gi-3/41)#switchport
Force10(conf-if-gi-3/41)#switchport backup gi 3/42
Force10(conf-if-gi-3/41)#no shutdown
R3
R4
3/41
3/42
4/31
4/32