A Quick Question - OSPF

[Jaylene]

An OSPF router has 3 directly connected networks;

172.16.0.0/16, 172.16.1.0/16 and 172.16.2.0/16

 Which OSPF network command would advertise only the

172.16.1.0 network

to neighbors?

   

A. rtr(config-router)# network 172.16.1.0 0.0.255.255 area 0
    B. rtr(config-router)# network 172.16.0.0 0.0.15.255 area 0
    C. rtr(config-router)# network 172.16.1.0 255.255.255.0 area 0
    D. rtr(config-router)# network 172.16.1.0 0.0.0.0 area 0

[luis_cordova]

Hi @Jaylene 

Correct answer is A

Regards

[Jaylene]

@luis_cordova  If we go for Option A, it will advertise the rest of the network as well.

[Giuseppe Larosa · Accepted solution]

Hello @Jaylene ,

both the question and all the answers have some errors.

First of all, the network ,mask cannot be

/16

on all three interfaces because this would lead to overlapping addresses that are not supported on real routers.

If you try to configure them in a real device or in an emulated one you get the address overapping error.

Given the

network addresses 172.16.0.0, 172.16.1.0, 172.16.2.0

the first prefix length that avoids overlapping is

/24

So the correct answer should be

network 172.16.1.0 0.0.0.255 area 0

as an alternative if the router inferface has

IP address 172.16.1.1

also the following will work

network 172.16.1.1 0.0.0.0 area 0

Hope to help

Giuseppe