Route summary question

You are correct. The 1st five bits of the 3rd octet can be summarized so

thanks for that -but the answer on the cisco quiz was /20 ? was it just an error.?

Both /24s so no nasty bits in the last octet. all we need worry about is the third as that is all that differs.

Your binary conversion is correct, and your observation is also correct. Five bits is the commonality.

You have. You have listened well on here. Now for the "correct" answer.

That is a mismatch between route and mask. 172.21.136.0 is a host address if the mask is /20.

The correct network ID from that mask and address is 172.21.128.0.

This is where I dislike computer based testing - if the question is wrong, you may be correct but you lose the mark. At least with the old proctor scored CCIE lab test you could argue your point with a human, in fact I think there were some parts where they actually wanted you to...

P.

Thanks for that-so the question was slightly incorrect?just hope they are all error free when I take my CCNA :)

It's a game. If you are genuinely good enough, the odd point or two from a dodgy question should not matter

That was what I liked about the old "interview scored" CCIE lab. You could configure something right, but throw the points away with a silly answer, or get something nearly there but with the right answer and attitude pull the points back.

P.