Reference Guide
0x67d4a14 0 2 18508 701 19878 ?
0x559972c 0 31 18508 209 18756 i
0x59cd3b4 0 2 18508 209 7018 15227 i
0x7128114 0 10 18508 209 3356 13845 i
0x536a914 0 3 18508 209 701 6347 7781 i
0x2ffe884 0 1 18508 701 3561 9116 21350 i
0x2ff7284 0 99 18508 701 1239 577 855 ?
0x2ff7ec4 0 4 18508 209 3561 4755 17426 i
0x2ff8544 0 3 18508 701 5743 2648 i
0x736c144 0 1 18508 701 209 568 721 1494 i
0x3b8d224 0 10 18508 209 701 2019 i
0x5eb1e44 0 1 18508 701 8584 16158 i
0x5cd891c 0 9 18508 209 6453 4759 i
--More--
Regular Expressions as Filters
Regular expressions are used to filter AS paths or community lists. A regular expression is a special character used to define a
pattern that is then compared with an input string.
For an AS-path access list, as shown in the previous commands, if the AS path matches the regular expression in the access list,
the route matches the access list.
The following lists the regular expressions accepted in the Dell Networking OS.
Regular
Expression
Definition
^ (caret) Matches the beginning of the input string. Alternatively, when used as the first character within brackets
[^ ], this matches any number except the ones specified within the brackets.
$ (dollar) Matches the end of the input string.
. (period) Matches any single character, including white space.
* (asterisk) Matches 0 or more sequences of the immediately previous character or pattern.
+ (plus) Matches 1 or more sequences of the immediately previous character or pattern.
? (question) Matches 0 or 1 sequence of the immediately previous character or pattern.
( ) (parenthesis) Specifies patterns for multiple use when one of the multiplier metacharacters follows: asterisk *, plus sign
+, or question mark ?
[ ] (brackets) Matches any enclosed character and specifies a range of single characters.
- (hyphen) Used within brackets to specify a range of AS or community numbers.
_ (underscore) Matches a ^, a $, a comma, a space, or a {, or a }. Placed on either side of a string to specify a literal and
disallow substring matching. You can precede or follow numerals enclosed by underscores by any of the
characters listed.
| (pipe) Matches characters on either side of the metacharacter; logical OR.
As seen in the following example, the expressions are displayed when using the show commands. To view the AS-PATH ACL
configuration, use the show config command in CONFIGURATION AS-PATH ACL mode and the show ip as-path-
access-list command in EXEC Privilege mode.
For more information about this command and route filtering, refer to Filtering BGP Routes.
The following example applies access list Eagle to routes inbound from BGP peer 10.5.5.2. Access list Eagle uses a regular
expression to deny routes originating in AS 32. The first lines shown in bold create the access list and filter. The second lines
shown in bold are the regular expression shown as part of the access list filter.
Example of Using Regular Expression to Filter AS Paths
Dell(config)#router bgp 99
Dell(conf-router_bgp)#neigh AAA peer-group
Dell(conf-router_bgp)#neigh AAA no shut
Dell(conf-router_bgp)#show conf
!
router bgp 99
Border Gateway Protocol IPv4 (BGPv4)
153