OSPF

[The_guroo_2]

i have bit confused can some one plz help me out:

suppose we have 3 routers which r located in three different sites (melbourne, hongkong, uk) i have dedicated link between them with class c ips.......and running ospf on them.

now tell me two things i know there will b no dr or bladdy bdr as they r not on broadcast domain......they have wan ips of /30 ok (using vlsm) now........they there is etehrnet as well on each routers which has say 200 pcs attached......

router A router B router C

serial 0 192.168.1.1/30 S0 192.168.1.2/30 S1 192.168.3.2/30

E0: 192.168.5.0/24 E0: 192.168.6.0/24 E0 192.168.7.0/24

S1 192.168.3.1/30

now the ideal command would b

RouterA (config)# router ospf 10

Network 192.168.1.1 0.0.0.0 area 0

redistribute connected subnets

and same for all............now mansoor bhai i m confuse abt one thing......this redistibute command one of my college told me.......why cany i put my etehrnet ip as well like newtwork 192.168.5.1 0.0.0.0 area 0 and so on for all routers..........secondly the wild card mask is 0.0.0.0 why its like that as i know rthat wildcard is inverse of subnet mask do dont u think that on serial it shd b 192.168.1.1 0.0.0.3 area 0 as its /252 actually............thirdly do we have to use always specific interface ip for ospf routes or we can use network no as well and in which scenario we use that (whole class like we do in rip and igrp)............so if i use network command for both serial and ethernet it does advertise etehrnet rouets but then the id of the router is etehrnet as it has the higgest ip as compare to serial secondly the route is shown as O........while if i use redsiribute command the route still shoes but it comes with O E2........what is that i know its called external route but whats the difference between two commands and this difference..hope u got my point............thanks for listing to crap..........i guess i m improving lil bit day by day :-) hoz chota..............hope everything is fine with ya

[balajitvk]

Hi,

Yes U can use network command for advertising ur LAN network with passive command on the ethernet interfac. By doing this instead of having redistribute command allows u to advertise as internal routes.

Next when u use wildcard mask 0.0.0.0, ur advertising only that particular ip insted of entire subnet by using wildcard mask of 0.0.0.3

For ur third question, it is not necessary only u have to advertise specific ip, u can advertise entire subnet as u do in other protocols.....

External routes are nothing but the routes advertised from other AS. So in some circumstances while taking routing decisions, internal routes will take precedance as compared to that external.

So that is disadvanatage when u use redistribute connected subnets instead of advertising using network command.

Hope this clears ur doubt.

Rate if it does,

Rgs

[olorunloba]

In addition note,

The network command in OSPF is used to tell the router on which interface it should start the OSPF process. What the router does is to use the arguments of the network command i.e. the network and the wildmask, and sees which interface or interfaces has an ip address in the range. For any interface that is in the range, the OSPF process is started on the interface.

Hence, the wildmask on the network command does not have to match the subnet mask of the interface ip address.