Re: BGP as-path access-lists

[A. Geoffrey Cauchi]

Hi   As regards the symbols:   ^    -    Beginning Of String, $    -    End Of String, _    -    Any Delimeter (beginning, end, whitespace, tab, comma), .    -    Any Single Character, +    -    matches one or more atoms, ?    -    matches zero or one atom,    *    -    matches zero or more atoms, ()    -    Can be used to group smaller regular expressions into larger expressions   Note atom => Sequence     With reference to your access-lists:   ip as-path access-list 1 permit  ^$ Here you are permitting IP addresses generated in your AS ip as-path access-list 4 permit  ^(_6774) +$ Permit AS 6774.  It does not have to be at the start, but it cannot be at the end. ip as-path access-list 10 permit  .*5413$ This permits AS5413 provided IP's are generated in this AS, due to the $ sign just after the AS number, but which are also passing through another AS, due to the . ip as-path access-list 6 permit  ^ (_3414) + (_2423) +$ Permit traffic going through AS3414 and AS2423.  The traffic is not generated in these AS's   Hope that this helps.  As regards links, these are quite good:   http://joe.lindsay.net/bgp.html http://www.cisco.com/pcgi-bin/tablebuild.pl/techdoc http://www.cisco.com/warp/public/459/18.html http://www.cisco.com/warp/public/459/13.html http://www.cisco.com/warp/public/459/13.html       ----- Original Message ----- From: Andre Fecteau Newsgroups: groupstudy.cisco To: [EMAIL PROTECTED] Sent: Wednesday, November 22, 2000 7:13 PM Subject: BGP as-path access-lists Hello, I have been recently placed in the awkward position of making some changes to our BGP configuration.  The problem is that I understand how bgp works for the main part, but I don't have any information on the meaning of the symbols used in the following as-path access-lists (^, $, _, ., +, (), *).  Could someone tell me what each of them mean?  Could someone also point me to a Cisco page that explains them in detail?  I have been searching and cannot find anything except examples that include these symbols.  Unfortuneately these examples have not helped my understanding.  I have a good idea as to what they probably mean, but I need to know their exact meaning.  It is difficult to manage something you don't have a clear understanding of! ip as-path access-list 1 permit  ^$ ip as-path access-list 4 permit  ^(_6774) +$ ip as-path access-list 10 permit  .*5413$ ip as-path access-list 6 permit  ^ (_3414) + (_2423) +$ HELP!!! Andre