Regarding IP default-network

[yangfrank]

Hi All

Please see the diagram in attachment. Anyone can help me understand the meaning of the question ? What is relation between 172.16.199.9 and 172.31.31.0/24 ? The correct answer is A and B. The command ip default-network should be followed by 172.16.0.0 instead of 172.16.199.9, right ?

Frank

[apasillas]

The ip default-network command is used mostly with routing protocols. The ip route command is used with static routing. Both are achieving the same goals but can be used in different scenarios. If you have a routing protocol for a domain, and you would like to advertise to the rest of the routers that a default route, you would implement the ip default-network command. This would cause the routing protocol to carry the candidate for default network in its routing updates to all routers in the domain.

The ip route 0.0.0.0 0.0.0.0 xx is a command that is statically assigned. This is called a default network because the all-zeros syntax means to catch all routes. The ip route command is not automatically carried in routing updates like the ip default-network command is in some routing protocols. You must redistribute the static command into a routing protocol for it to be carried.

[Ashok Kumar]

Hi,

When you configure ip default-network the router considers routes to that network for installation as the gateway of last resort on the router.

Long story in short is, You understood correctly. 

ip default-network makes the routes candidate default route.

2513#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
2513(config)#ip route 171.70.24.0 255.255.255.0 131.108.99.2
2513(config)#ip default-network 171.70.24.0
2513(config)#^

Below is a very good article on this, you must read

Configuring a Gateway of Last Resort Using IP Commands

http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/16448-default.html

- Ashok

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