Default-Network command in RIP

Network3-----R1-----R2------Network4

The networks in the above exhibited are all configured with RIP. On router R1, the following configuration change was made:

R1(config)#ip default-network 'Network 3'

Which router will receive a default route as a result of this change?

A. Router R1 only-

B. Router R2 only.

C. Both routers.

D. Neither router.

Reply to
Saad Ahmed
Loading thread data ...

D

Jonathan

Reply to
Jonathan

Saad, I must confess I had to lab this one up to prove it to myself as I had a faulty or out-dated memory about this command. Currently under IOS

12.2(23), when applying the IP DEFAULT-NETWORK command to R1 with RIPV2 active, R2 receives a default route - that looks like this:

R2#sho ip route Gateway of last resort is 10.10.1.1 to network 0.0.0.0 10.0.0.0/24 is subnetted, 1 subnets C 10.10.1.0 is directly connected, Ethernet0 R 200.10.10.0/24 [120/1] via 10.10.1.1, 00:00:09, Ethernet0 R* 0.0.0.0/0 [120/1] via 10.10.1.1, 00:00:10, Ethernet0

R1 gets the route flagged with an asterisk but as is a connected route, the Gateway of Last Resort is not set - as follows:

R1#sho ip route Gateway of last resort is not set 10.0.0.0/24 is subnetted, 1 subnets C 10.10.1.0 is directly connected, Ethernet0 C* 200.10.10.0/24 is directly connected, Ethernet1 150.50.0.0/24 is subnetted, 1 subnets R 150.50.1.0 [120/1] via 10.10.1.2, 00:00:06, Ethernet0

The command was applied to R1 as IP DEFAULT-NETWORK 200.10.10.0

FWIW, Robert

Reply to
Bob by the Bay

Also, my understanding is that this automatic incorporation of the IP DEFAULT-NETWORK into the routing protocol is only extended to RIP and IGRP (both classful routing protocols). And in fact, since IGRP doesn't understand the command IP ROUTE 0.0.0.0 0.0.0.0, the IP DEFAULT-NETWORK command is even more meaningful in IGRP.

Robert

Reply to
Bob by the Bay

My conclusion is that R2-only receives the default route as a result of the configuration of IP DEFAULT-NETWORK on R1

Reply to
Bob by the Bay

Thanks Bob for doing the hard work :) By the way then would u go with A?

Reply to
Saad Ahmed

This is correct. In RIP, ip default-network xxxxx will advertise a candidate default route (0.0.0.0/0) bit will not install it locally. To have a default network locally on R1, you would have to configure a static route: ip route 0.0.0.0 0.0.0.0 xxxxx

Here is the link:

formatting link
"Gateways of last resort selected using the ip default-network command are propagated differently depending on which routing protocol is propagating the default route. For IGRP and EIGRP to propagate the route, the network specified by the ip default-network command must be known to IGRP or EIGRP. This means the network must be an IGRP- or EIGRP-derived network in the routing table, or the static route used to generate the route to the network must be redistributed into IGRP or EIGRP, or advertised into these protocols using the network command.

RIP advertises a route to 0.0.0.0 if a gateway of last resort is selected using the ip default-network command."

Doan

Reply to
Doan

Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.