Hello,
In the 18-19 Exam, Problem 2/Q1(a)(ii), the distances from C3 to the 2 destination networks 2001:1::/32 and 2001:2::/32 are the same: 112
When calculating the distance, do we not take into account the cost of the links inside the destination AS?
For example, shouldn't the distance from C3 to 2001:2::/32 be 113, as there are 2 hops between A2 and A4 ? (From C3 to 2001:2::/32, I count 1 +10 + 100 + 1 + 1)
Thank you!
Hello,
Actually the confusion comes from the fact that BGP does not propagate distances in its attributes.
So in order to compute the distance, you need to compute the distance between your router and the next BGP hop.
In the case of B3, the cost to go from B3 to a B2 is 1 and then the cost to the next BGP router (A2) is 100+1=101 because of the following sentence "
When redistributing E-BGP into OSPF, the OSPF cost of the redistributed route is set to the OSPF cost to the BGP next-hop plus 100." As a result the cost from B3 to the stub networks in AS A is 102.
In the case of C3, the cost to go from C3 to C2 is 11, then from C2 the cost to stub networks in AS A is 100+ 1(line A2-C2), which makes a total of 101+11=112.
I hope that this clarifies your misunderstanding.
Best regards,
Marguerite
Ok, I see. Yes, this definitely clarifies my misunderstanding.
Thank you very much!
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