Route Redistribution

More than one routing protocol can be enabled simultaneously on a network. Route redistribution allows the switch to exchange routes, including static routes, between the active routing protocols. The following figure shows a network that is running two routing protocols, IS-IS and RIP.

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AS External Route Redistribution
../Graphics/EX_isis_0024.svg

By default, the IS-IS/RIP node does not inject its learned RIP routes into IS-IS—and it does not need to if originate-default feature is enabled using the command:

enable isis area area_name originate-default {ipv4 | ipv6} .

If it does redistribute the RIP routes into IS-IS, all L2 IS-IS routers learn the RIP routes as type IS-IS level 2 external. The L2 IS-IS routers do not know that the routes actually originated from RIP. Also, if configured to do so, L1/L2 routers can leak these routes into the L1 areas and all IS-IS routers learn the RIP routes (without knowing that they actually came from RIP and without having to actually participate in RIP).

Route redistribution is configurable on both L2 and L1 using the enable isis area export commands. Redistributing routes into L1 generates L1 external routes. The export policy can choose to redistribute external routes with internal metrics into IS-IS.