Network Interface Backup configuration

Network Interface Backup protects against a single point of network failure by providing failure detection and failover with no disruption to user connections. When operating in this mode, only one adapter is active at any given time.

If the active adapter fails, another adapter in the EtherChannel will be used for all traffic. When operating in Network Interface Backup mode, it is not necessary to connect to EtherChannel-enabled switches.

The Network Interface Backup setup is most effective when the adapters are connected to different network switches, as this provides greater redundancy than connecting all adapters to one switch. When connecting to different switches, make sure there is a connection between the switches. This provides failover capabilities from one adapter to another by ensuring that there is always a route to the currently-active adapter.

Priority is given to the adapter configured in the primary EtherChannel, over the backup adapter. As long as the primary adapter is functional, it is used. This contrasts from the behavior of Network Interface Backup mode in earlier releases, where the backup adapter was used until it also failed, regardless of whether the primary adapter had already recovered.

For example, ent0 could be configured as the main adapter, and ent2 as the backup adapter, creating an EtherChannel called ent3. Ideally, ent0 and ent2 would be connected to two different switches. In this example, all traffic sent over ent3 (the EtherChannel's interface) is sent over ent0 by default, whereas ent2 is idle. If at any time ent0 fails, all traffic is sent over the backup adapter, ent2. When ent0 recovers, it is again used for all traffic.

It is now possible to configure the EtherChannel to detect link failure and network unreachability for multiple EtherChannels with a backup adapter. To do this, use the netaddr attribute to specify the IP address or host name of a remote host where connectivity should always be present. The EtherChannel will periodically ping this host to determine whether there is still a network path to it. If a specified number of ping attempts go unanswered, the EtherChannel will fail over to the other adapter in the hope that there is a network path to the remote host through the other adapter. In this setup, not only should every adapter be connected to a different switch, but each switch should also have a different route to the host that is pinged.

This ping feature is available for one or more EtherChannels with a backup adapter. However, if there is a failover due to unanswered pings on the primary adapter, the backup adapter remains the active channel as long as it is working. There is no way of knowing, while operating on the backup adapter, whether it is possible to reach the host being pinged from the primary adapter. To avoid failing over back and forth between the primary and the backup, it keeps operating on the backup (unless the pings go unanswered on the backup adapter as well, or if the backup adapter itself fails, in which case it would fail over to the primary adapter). However, if the failover occurred because the primary adapter failed (not because the pings went unanswered), the EtherChannel will then come back to the primary adapter as soon it has come back up, as usual.

To configure Network Interface Backup in the newer versions, see Configuring Network Interface Backup.