Route Filter

up2thetime

Hey everyone,

Going through Junos Genius and came across a question I don't understand.

Give the following statement:

route-filter 192.168.0.0/16 longer

Which three routes would match (choose three):

A. 192.168.0.0
B. 192.168.0.1
C. 192.168.1.0
D. 192.168.255.254
E. 192.169.0.0

The correct answer is B, C, and D. No subnet masks were provided.

Why is A not correct? I understand that longer means that 192.168.0.0 /17 to /32 will be matched, and that /16 will be excluded. However, how do we know that A is not 192.168.0.0/17? The question does not provide the subnet masks, so A could be a /17 or a /18 (or something longer).

Also, why is B, C, and D correct? We have no way of knowing whether B, C, and D are actually part of /16 networks. B could actually be 192.168.0.1/16, but we cannot determine this since no mask was provided. For B and C to be correct we have to assume that they come with a /17 or longer mask, but the question doesn't give you that information.

Anyway, just wondering why A is incorrect, and why B, C, and D are.

Thanks!

Trashman

Good evening,

I believe the question is asking which three of five routes would match when the router filter with 192.168.0.0/16 is applied.

"Longer" matches if the prefix-length is greater than the route’s prefix length.

A is the prefix-length -- B, C and D are greater.
E is ignored because it's 192.169

Correct me if I'm wrong