02-14-2006 09:02 AM - edited 03-03-2019 11:44 AM
Dose any one knows good link or reference material I can use to understand BGP as-path regular expressions for route filtering. I have basic understanding but just in case if I can understand this in depth I am looking for as many as regular expression examples with explanation
Thanks
Rits
02-14-2006 09:13 AM
Rits,
These may help!
http://www.quagga.net/docs/docs-multi/AS-Path-Regular-Expression.html
http://www.cisco.com/warp/public/459/26.html
http://www.avici.com/documentation/HTMLDocs/02223-06_revBA/Routing_Pol7.html
HTH
Sankar.
02-15-2006 01:51 PM
If you haven't got access to a test network, when you have studied how reg expressions work try...
http://www.netdigix.com/servers.html
It's a list of public route servers.You are allowed access to do sh ip bgp regexp
Rgds
E.
02-16-2006 01:19 PM
This info might be helpful for your needs
Range
A range is a sequence of characters contained within left and right square brackets. For example: [abcd]
Atom
An atom is a single character, such as the following:
. (Matches any single character)
^ (Matches the beginning of the input string)
$ (Matches the end of the input string)
\ (Matches the character)
- (Matches a comma (,), left brace ({), right brace (}), the beginning of the input string, the end of the input string, or a space.
Piece
A piece is an atom followed by one of the following symbols:
* (Matches 0 or more sequences of the atom)
+ (Matches 1 or more sequences of the atom)
? (Matches the atom or the null string)
Branch
A branch is a 0 or more concatenated pieces.
Examples of regular expressions follow:
a* (Any occurrence of the letter "a", including none)
a+ ( At least one occurrence of the letter "a" should be present)
ab?a (This matches "aa" or "aba")
_100_ (Via AS100)
_100$ (Origin AS100)
^100 .* (Coming from AS100)
^$ (Originated from this AS)
Refer to Using Regular Expressions in BGP for sample configurations on regular expression filtering
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