prefix-list question

crrimson

I've been racking by brain on this, and I think the way I'm thinking about this problem is causing me to make prefix-lists seem harder than they should be.

Can you do this?
Block ranges 10.17.80.0 - 10.17.255.255 with a single prefix-list statement?

C 10.17.0.0/19 is directly connected, Loopback5
C 10.17.32.0/20 is directly connected, Loopback1
C 10.17.80.0/20 is directly connected, Loopback3
C 10.17.64.0/20 is directly connected, Loopback2
C 10.17.96.0/20 is directly connected, Loopback4
C 10.17.128.0/17 is directly connected, Loopback6

Thanks

pogue

Hmmm...

Look at the first few bits of the 3rd octet.. That is the first part the prefix list matches on..

If you match on 17 bits, it covers range of either 0-127, or 128-255.

If you match on 18 bits.. You have to pick a range of 0-63, 64-127, 128-191, 192-255.

Etc, etc..etc..

I think the closest you can get is using ip prefix-list mindbender seq 5 deny 10.17.64.0/18 ge 20. If I am right, (remember, I am still studying for the CCNP ROUTE) this covers 10.17.64.0/20 -10.17.96.0/20 out of the list above, but not 10.17.128.0/20, as this network requires one to change the third octet first two bits to 10, instead of 01.

Again, I think this is correct.. If I am proven wrong, I will edit my post and defer to the experts.

By the way..Why do you have to do it with one line instead of multiple?

Russ

Using this math, any of the above networks that has a 01xxxxxx in the third octet will be filtered.