Thanks for all of that detail. I think the book was in error then for not including the 10.17.36.128/26 and the 10.17.36.192/26 networks. I guess the only thing I am still confused about is why does the first line of the prefix-list work for 10.17.35 using the "ge 25 le 25" but NOT work for 10.17.36 using "ge 25 le 25"?
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I am new to prefix-lists and I'm trying to understand them better. I have been using the CCNP Routing and Switching ROUTE 300-101 Cisco Press book to aid in my understanding and I'm having trouble following one of the examples about prefix-lists and wanted to see if anyone could shed some light on it for me.
One of the goals in the example is to filter routes that begin with 10.17.35 and 10.17.36 from a larger range of 10.17.32.0-10.17.63.255. Per the example this is accomplished with the following two lines:
ip prefix-list fred seq 5 deny 10.17.35.0/24 ge 25 le 25
ip prefix-list fred seq 10 deny 10.17.36.0/24 ge 26 le 26
The explanation given is that the first line (sequence number 5) matches 10.17.35.0 /25 and 10.17.35.128 /25. I understand this because it would include the IP range of 10.17.35.0-10.17.35.255. However, the explanation for the 2nd line (sequence number 10) is confusing to me: "Similarly, the second statement matches routes 10.17.36.0 /26 and 10.17.36.64 /26." So wouldn't this only cover the IP range of 10.17.36.0-10.17.36.127? What about the range 10.17.36.128-10.17.36.255? And why would this 2nd line use 26 as the prefix length and not use the following which is similar to the first line?:
ip prefix-list fred seq 10 deny 10.17.36.0/24 ge 25 le 25
Perhaps I am missing something fundamental either with prefix-lists or with IP subnetting in general. I would appreciate any feedback or suggestions for better understanding this. Thank you.
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