Cisco IOS policy route default traffic

When migrating for instance firewalls it might come in handy to push all default traffic without a specific route in the RIB towards another next-hop. To do this on Cisco IOS, we have to use route-maps. The ip default next-hop stanza will make sure everything that has no entry in the RIB (0.0.0.0/0 is ignored) will be routed towards that next-hop.

In this example we route all default traffic coming on interface Vlan100 towards 10.42.255.254:

route-map outgoing-new-fw permit 1
 set ip default next-hop 10.42.255.254
!
interface Vlan100
 ip policy route-map outgoing-new-fw

We can also do the same for specific source ranges on the interface:

ip access-list extended pfx-outgoing-new-fw
 permit ip 10.42.1.0 0.0.1.255 any
 deny ip any any
!
route-map outgoing-new-fw permit 1
 match ip address pfx-outgoing-new-fw
 set ip default next-hop 10.42.255.254
!
interface Vlan100
 ip policy route-map outgoing-new-fw