Gateway of last resort is not set In Cisco Router or Switch
You may notice the Line “gateway of last resort is not set”
in output when you use the cisco command Show IP Route. This short article will
explain that why you are getting this message.
Cisco router gateway of last resort
"Gateway of Last Resort is not set” means that there is no default
route for IP packets which have no match with routing table. Gateway of last
resort are routes use to avoid your router from dropping packets with unknown
networks those are not exist in routing table
Routing table have the list of all known routes. Every time
when a router receives a packet, router matches it with routing table entries if
it present in routing table then it forward to that path and if route not present
in routing table then it is forwarded to default gateway or default route.
How to set Gateway of last resort in router
You can configure or set a default gateway, or route of last
resort with following commands:
- ip default-network
- ip default-gateway
- ip route 0.0.0.0 0.0.0.0
ip
default-gateway
The ip default-gateway command is used when ip routing is
disabled on Cisco-router. Following example defines the default route on router
to 172.16.15.4:
ip default-gateway 172.16.15.4
Instead of ip default-gateway command,
you can use ip default-network when ip routing is enabled
on Cisco-router. When you configure ip default-network the router
considers routes to that network for installation as the gateway of last resort
on the router. Gateways of last resort selected using the ip
default-network command are advertised differently depending on which
routing protocol is advertise the default route. For IGRP/EIGRP to propagate
the route, the network specified by the ip default-network command
must be known to IGRP or EIGRP.
RIP advertises a route to 0.0.0.0 if a gateway of last resort
is selected using the ip default-network command.
The default route advertised with
the ip default-network command
is not propagated by IS-IS and OSPF.
IP Route
0.0.0.0
Creating
a static-route to unknown network is another way to set the gateway of last
resort on a router. IGRP does not recognize a route advertise with static route
command to 0.0.0.0. You are required to use the ip default-network command in case of IGRP. EIGRP advertise a
route to network 0.0.0.0, but the static route must beredistributed into the routing protocol.
RIP routers running Cisco IOS 12.0T and later does not advertise the default route
where as in earlier version it automatically create a default route 0.0.0.0.
Summary:
Use the ip default-gateway command if the ip routing is
disabled on Cisco-router and Use the ip default-network and ip route 0.0.0.0 0.0.0.0 commands
to set the gateway of last resort on Cisco routers that have ip routing enabled.
The way in which routing-protocols advertise
the default route differs for each protocol.
Quick Tip:
For setting network of last resort like use the following
command:
ip default-network <IP
address of gateway>
