help with route summarization please

newtechie1988

Hey there,
I am in my 2nd semester cisco networking. We are currently learning route summarization. I understand how to summarize a route but how do I do the reverse. for example when I am given the summarized route 172.168.8.0/21, how do I find out what the areas of networks it covers?
Could somebody please tell me and then give me some examples?
Thank you

jdfriesen

newtechie1988 wrote: »

Hey there,
I am in my 2nd semester cisco networking. We are currently learning route summarization. I understand how to summarize a route but how do I do the reverse. for example when I am given the summarized route 172.168.8.0/21, how do I find out what the areas of networks it covers?
Could somebody please tell me and then give me some examples?
Thank you

That's just a subnetting question. You just have to figure out the address range that 172.168.8.0/21 covers. /21 is equivalent to 255.255.224.0. That gives you a block size of 32 (256-224). In the case of your example, we actually have an error, because the first two subnets in the 172.168.0.0/21 range would be:

• 172.168.0.0
• 172.168.32.0

So, assuming that the original example was 172.168.32.0/21, then the covered addresses would be 172.168.32.0 - 172.168.63.255 (as 172.168.64.0 would be the next subnet).