How do I make a backup route that only activates when the primary fails?

Question

We have a fast primary link and a slow backup. I want traffic on the primary normally, failing over automatically. Can statics do this without a routing protocol?

NetForge Team · Accepted Answer

Yes — a **floating static route**. Configure the backup with a worse administrative distance than the primary: `ip route 0.0.0.0 0.0.0.0 203.0.113.1` (primary, AD 1) and `ip route 0.0.0.0 0.0.0.0 198.51.100.1 250` (backup, AD 250). The routing table installs only the best AD, so the backup "floats" invisible until the primary is withdrawn — which happens when its exit interface goes **down**. That's the catch: if the primary fails somewhere the router can't see (the far end of a carrier circuit, interface still up/up), the static never withdraws and the float never engages. That failure mode is exactly what IP SLA tracking or a real routing protocol solves; for the classic lab/exam scenario, interface-down failover with AD 250 is the expected answer.

How do I make a backup route that only activates when the primary fails?

1 Answer

Your answer