38. Link Failover
ROX™ v2.2 User Guide
416
RuggedBackbone™ RX5000
38. Link Failover
Link failover provides an easily configured means of raising a backup link upon the failure of a
designated main link. The main and backup links can be Ethernet only.
Link failover can back up to multiple remote locations, managing multiple main-to-backup link
relationships.
Link failover can back up a permanent, high-speed WAN link to a permanent, low-speed WAN link. Use
this function when OSPF cannot be employed, such as on public links.
You can also use link failover to migrate the default route from the main link to the backup link.
The time after a main link failure to backup link startup, and the time after a main link recovery to backup
link stoppage, are configurable. The link failover function also provides failover status information and
a test of the failover settings.
38.1. Path Failure Discovery
To discover a primary path failure (in this example, through Network A), the link backup daemon inspects
the link status of the main link and sends a regular ping to a designated host (or to a dummy address
on the router). In this way, network link failures can be discovered. It is essential that the designated
host or that the dummy address always respond to the ping.
Figure 38.1. Link Backup Example
The daemon considers the main link to have failed, even if its link status is “up”, if the remote host fails
to respond to a configurable number of pings after waiting a configurable timeout for each ping.
38.2. Using Routing Protocols and the Default Route
If the main trunk is on a private network, use a routing protocol to ensure that an alternate route to the
end network is learned after the backup trunk is raised. Ensure that OSPF/RIP are configured to operate
on the secondary trunk, assigning the secondary trunk a higher metric cost than that of the main trunk.
If the main trunk is on a public network, use the “transfer default route” feature.
The default route of the main trunk to be backed up using “transfer default route” must be
assigned a metric greater than one.
38.3. Configuring Link Failover
To view the list of configured link failover settings, navigate to /services/link-failover.
