Alternative Routes

Table 1. Alternative routes product support

Feature	Product	Release introduced
Alternative routes for IPv4	5320 Series	Fabric Engine 8.6
	5420 Series	VOSS 8.4
	5520 Series	VOSS 8.2.5
	5720 Series	Fabric Engine 8.7
	7520 Series	Fabric Engine 8.10
	7720 Series	Fabric Engine 8.10
	VSP 4450 Series	VSP 4000 4.0
	VSP 4900 Series	VOSS 8.1
	VSP 7200 Series	VOSS 4.2.1
	VSP 7400 Series	VOSS 8.0
	VSP 8200 Series	VSP 8200 4.0
	VSP 8400 Series	VOSS 4.2
	VSP 8600 Series	VSP 8600 4.5
	XA1400 Series	VOSS 8.0.50
Alternative routes for IPv6	5320 Series	Fabric Engine 8.6
	5420 Series	VOSS 8.4
	5520 Series	VOSS 8.2.5
	5720 Series	Fabric Engine 8.7
	7520 Series	Fabric Engine 8.10
	7720 Series	Fabric Engine 8.10
	VSP 4450 Series	VOSS 5.1
	VSP 4900 Series	VOSS 8.1
	VSP 7200 Series	VOSS 5.1
	VSP 7400 Series	VOSS 8.0
	VSP 8200 Series	VOSS 5.1
	VSP 8400 Series	VOSS 5.1
	VSP 8600 Series	VSP 8600 6.2
	XA1400 Series	Not Supported

To avoid traffic interruption, you can globally enable the alternative routes feature so the router can use the next-best route, also known as an alternative route, if the best route becomes unavailable.

Routers learn routes to a destination through routing protocols. Routers maintain a routing table of the learned alternative routes sorted in order by route preference, route costs, and route sources. The first route on the list is the best route and the route that the router prefers to use.

The alternative route concept also applies between routing protocols. For example, if an OSPFv3 route becomes unavailable and an alternative RIPng route is available, the system activates the RIPng route without waiting for the update interval to expire.