From: Jonathan V Hays (jhays@jtan.com)
Date: Thu Jul 17 2003 - 17:25:17 GMT-3
Well, let's try these regular expression out. There's any easy way to do
this using the "show ip bgp quote-regexp" to test.
To review, we are trying to filter routes that originate in AS 100.
Here's a BGP table with no filter:
----------
r2#sh ip bgp
BGP table version is 3, local router ID is 10.1.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 99.99.99.0/24 10.1.1.1 0 0 9 100 i
*> 130.108.1.0/24 10.1.1.1 0 0 9 i
r2#
----------
Here's how to test. Let's match only networks originating from AS 9:
The modifier "| include 10.1.1.1" cuts down on unneeded output.
r2#sh ip bgp quote-regexp 9$ | include 10.1.1.1
*> 130.108.1.0/24 10.1.1.1 0 0 9 i
----------
Only networks originating from AS 100:
r2#sh ip bgp quote-regexp 100$ | include 10.1.1.1
*> 99.99.99.0/24 10.1.1.1 0 0 9 100 i
r2#
----------
The filter from Des doesn't match anything:
r2#sh ip bgp quote-regexp _^100$
r2#
I don't know if the regexp function understands the _^ sequence, since
the ^ in this context means 'beginning of line.' I think the ^ can only
be used for negation inside a character class.
----------
My own suggested filter does not match either:
r2#sh ip bgp quote-regexp [^1][^0][^0]$
r2#
----------
After I thought about it, I realized that the desired entry (with only
AS 9 in the path) won't match either since it only has one digit and the
regexp is looking for 3 digits.
If we change the regex so the last digit only matches anything but a
zero, that would work, but wouldn't meet the requirements, since 10,
200, 50, would also match.
r2#sh ip bgp quote-regexp [^0]$ | include 10.1.1.1
*> 130.108.1.0/24 10.1.1.1 0 0 9 i
r2#
----------
In UNIX or Perl regular expressions you might use the a bang
(exclamation point) to negate an expression, as in !(100)$ but that does
not seem to work in IOS.
r2#sh ip bgp quote-regexp !(100)$ | include 10.1.1.1
r2#
----------
I'm stumped but at least now you all can see how to test a regular
expression.
HTH,
Jonathan
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