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Question on which of these 3 hops traffic would take ?

news2010a
Level 3
Level 3

Regarding the question below, can someone confirm how you determine which route it would take ?

If you write the next hop information in binary to compare against the target route, you have to do that for "via 153.2.220.2", for example ? Is that correct ? That's the next hop info you are looking for, not the "153.2.25.0/23" info.

Question:

If a packet is sent to 153.2.25.66, which next hop it would take ?

S 153.2.25.0/23 [1/0] via 153.2.220.2

O E2 153.2.25.0/25 [110/20] via 153.2.230.2,serial0/0

R 153.2.25.0/26 [120/1] via 153.2.1.1,e0/1

3 Replies 3

Hi,

The router would use the OSPF route, 153.2.25.0/25, to forward packets to the host 153.2.25.66.

The reason why it doesn't use static or RIP route is because, routing decisions are based on the longest match. The OSPF route covers anything between 153.2.25.0 - 153.2.25.127. Static route covers anything between 153.2.24.0 - 153.2.25.255. RIP route covers the range 153.2.25.0 - 153.2.25.63.

As you can see, the OSPF route is more specific than the static route, which covers a wider range. The RIP route doesn't include the host, 153.2.25.66, in its route at all. Admin distance acts as the tie-breaker only if the route/mask is the same.

I am not sure what do you mean the subnet mask isn't given the /xx after the route is the mask for the route.

Hope this helps!

Sundar

Thanks. I got it.

dwilsonccna
Level 1
Level 1

The OSPF route would be the route to that destination network because it has the longest match.

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