Alcatel-Lucent 6850 Switch User Manual


 
BGP Overview Configuring BGP
page 4-14 OmniSwitch 6800/6850/9000 Advanced Routing Configuration Guide December 2007
It makes writing (and reading) policies much easier.
It enables the router to begin using the policies more quickly after startup.
For example, to identify routes originating from internal autonomous systems, you would use the pattern:
[64512-65535]$
which means “match any AS number from 64512 to 65535 (inclusive) which occurs at the end of the AS
path.” To accomplish the same thing using character-based pattern matching, you would have to use the
following pattern:
(_6451[2-9]_|_645[2-9][0-9]_|_64[6-9][0-9][0-9]_|_65[0-9][0-9][0-9]_)$
Some examples of valid regular expressions are shown in the following table:
Example Description
100 Meaning: Any route which passes through AS number 100.
Matches: 100 200 300
300 100 100
Doesn’t Match: 200 300
^100 Meaning: Any routes for which the next hop is AS number 100.
Matches: 100 200 100
Doesn’t Match: 50 100 200
100$ Meaning: Any route which originated from AS number 100 (AS numbers are
prepended to the AS path list as they are passed on, so the originat-
ing AS is always the last number in the list).
Matches: 100
200 200 100
Doesn’t Match: 100 200
^100 500$ Meaning: A route with just two hops, 100 and 500.
Matches: 100 500
Doesn’t Match: 100 500 600
100 200 500
100 . . 200 Meaning: Any route with at least 4 hops, with 100 separated by any two hops
from 200.
Matches: 50 100 400 500 200 600
100 100 100 200
Doesn’t Match: 100 200
100 100 200
(100|200).+
[500-650]$
Meaning: Any route which begins with 100 or 200, ends with an AS number
between 500 and 650 (inclusive), and is at least three hops in length.
The “.+” part matches at least one (but possibly more) AS numbers.