Quiz 11, question 10

Quiz 11, question 10

by Milan Duric -
Number of replies: 1

Hello,

I just want to make sure I understand the reasoning behind the correct answer here.

Is this because:

  1. OSPF treats 2001:620:619::/48 and 2001:620::/32 as two different stub networks (connected to two different OSPF routers), meaning both of them will be included in router LSAs and both of them will be two separate nodes in the graph, which means we will in the end add both of them to the routing table. By longest prefix match, we will select a route to 2001:620:619::/48 which leads us to AS X
  2. In FRR and cisco, BGP always injects routes into forwarding table, even if these routes are redistributed into IGP. This means 2001:620:619::/48 will for sure be injected by E-BGP with next hop some router in X. This forwarding table entry will have a smaller administrative distance than whatever OSPF injects.

    Many thanks in advance.

In reply to Milan Duric

Re: Quiz 11, question 10

by Plouton Grammatikos -

Hello,

You are right in both your points, however the administrative distance does not matter here. The purpose of the admin distance is to resolve conflicts in case there are two routes to the same prefix. In case there is a single route with the longest prefix, then there is always a priority given to that route.