Prefix-list help [7:72090]
Classless domain -R1--classful domain R1 is the border router between the classless and classful routing domain. R1 maintains a BGP peering session with the classless routing domain, and runs a classful IGP with the classful routing domain. The classless routing domain is originating a default route to R1 via BGP, and advertising prefixes which are subnetted, aggregated, and classful. Since the classful routing domain does not support the advertisement of subnets or aggregates, there is no reason for R1 to accept any of these prefixes in from the classless domain. Configure an access-list or prefix-list on R1 that will only allow classful networks and a default route in from the classless routing domain. This access-list or prefix-list should not contain more than four entries. I think this will work but not sure. Can anyone tell me if this is right? ip prefix-list test seq 5 permit 0.0.0.0/0 ip prefix-list test seq 5 permit 0.0.0.0/0 ge 8 le 8 ip prefix-list test seq 5 permit 0.0.0.0/0 ge 16 le 16 ip prefix-list test seq 5 permit 0.0.0.0/0 ge 24 le 24 Any help is duly appreciated in advance. Thanks Raj Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=72090t=72090 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Prefix-list help [7:72090]
Hi, I would suggest the following: ip prefix-list test seq 5 permit 0.0.0.0/0 ip prefix-list test seq 10 permit 0.0.0.0/1 ge 8 le 8 ip prefix-list test seq 15 permit 128.0.0.0/2 ge 16 le 16 ip prefix-list test seq 20 permit 192.0.0.0/3 ge 24 le 24 Your solution wouldn't filter out those subnets and aggregates whose netmask falls on a classful boundary. And of course the sequence numbers must be different for each entry. :) Thanks, Zsombor At 07:14 AM 7/10/2003 +, Raj Singh wrote: Classless domain -R1--classful domain R1 is the border router between the classless and classful routing domain. R1 maintains a BGP peering session with the classless routing domain, and runs a classful IGP with the classful routing domain. The classless routing domain is originating a default route to R1 via BGP, and advertising prefixes which are subnetted, aggregated, and classful. Since the classful routing domain does not support the advertisement of subnets or aggregates, there is no reason for R1 to accept any of these prefixes in from the classless domain. Configure an access-list or prefix-list on R1 that will only allow classful networks and a default route in from the classless routing domain. This access-list or prefix-list should not contain more than four entries. I think this will work but not sure. Can anyone tell me if this is right? ip prefix-list test seq 5 permit 0.0.0.0/0 ip prefix-list test seq 5 permit 0.0.0.0/0 ge 8 le 8 ip prefix-list test seq 5 permit 0.0.0.0/0 ge 16 le 16 ip prefix-list test seq 5 permit 0.0.0.0/0 ge 24 le 24 Any help is duly appreciated in advance. Thanks Raj Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=72139t=72090 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Prefix-list help [7:72090]
LOL, thanks I got this like 10 mins before I got your email. I went of a search spree, and found the answer. Here is what I found, its all binary. This will permit the default route ip prefix-list test seq 5 permit 0.0.0.0/0 This will look at the first bit of the first octet and will match the netmask to 8 bit ip prefix-list test seq 5 permit 0.0.0.0/1 ge 8 le 8 This will look at the first 2 bits of the first octet 1000 and match the netmask to 16 bit ip prefix-list test seq 5 permit 128.0.0.0/2 ge 16 le 16 This will look at the first 3 bits of the first octet 1100 and match the netmask to 24 bit ip prefix-list test seq 5 permit 192.0.0.0/3 ge 24 le 24 Thank you very much for all your help. Really appreciate it Raj Singh Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=72140t=72090 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
