Questions about static routes and GW of last resort

Hello !

I'm currently doing a huge mix with the following notions : static routes, gateway of last resort...

I've read the following notes from Cisco

http://www.cisco.com/warp/public/105/default.html

It helped me, but there are still some things that I don't undertand like :

- What is the exact meaning of "gateway of last resort" ?

- What does "candidate default route" mean ?

- What does "flag a default network" mean ?

- In the "ip default-network" section, they say :

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

Why the ip default-network 171.70.24.0 command is not sufficient ?

- Is the "default-information originate" used also with IGRP protocol (as we do with OSPF and IS-IS protocols according to these Cisco notes) ?

...

Thanks

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Comments

steve-o87

A gateway of last resort is when the router cant find a route for a packet in it's routing table, it will then forward these packets out of the gateway of last resort.

A flag is just a marker, if a route is flagged it has been marked. So in our case the route has been marked as the default.

The default-information originate command is used with ospf to create a special type 3 LSA.

Quote:
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

Why the ip default-network 171.70.24.0 command is not sufficient ?

I dont quite know what you mean here?!?!

Most of this stuff isn't needed for the CCNA anyway. It's not bad to know it but this kind of thing is more CCNP material

GOOD LUCK!

EdTheLad

ip default-network is a classful command, it works at the major network boundary.You are only supposed to use the major network when using this command.If you type the command default-network 171.70.24.0 the ios will create a route from the major network 171.70.0.0/16 to the subnet 171.70.24.0, this is to help you, next when you type default-network 171.70.0.0 the command will execute correctly as you have specified the major network and sinceas there is a route between 171.70.0.016 and 171.70.24.0, 172.70.24.0 will be marked as the gateway of last resort.

When you execute ip default-network on two different major networks one will become the gateway of last resort and one will be marked as candidate, this means if the current gateway fails the candidate will be used as a backup gateway.