Dell S4820T Configuration Manual page 233

Regular Expression Definition
_ (underscore) Matches a ^, a $, a comma, a space, or a {, or a }. Placed on either side of a string to
specify a literal and disallow substring matching. You can precede or follow
numerals enclosed by underscores by any of the characters listed.
| (pipe) Matches characters on either side of the metacharacter; logical OR.
As seen in the following example, the expressions are displayed when using the show commands. To
view the AS-PATH ACL configuration, use the show config command in CONFIGURATION AS-PATH
ACL mode and the show ip as-path-access-list command in EXEC Privilege mode.
For more information about this command and route filtering, refer to
The following example applies access list Eagle to routes inbound from BGP peer 10.5.5.2. Access list
Eagle uses a regular expression to deny routes originating in AS 32. The first lines shown in bold create
the access list and filter. The second lines shown in bold are the regular expression shown as part of the
access list filter.
Example of Using Regular Expression to Filter AS Paths
Dell(config)#router bgp 99
Dell(conf-router_bgp)#neigh AAA peer-group
Dell(conf-router_bgp)#neigh AAA no shut
Dell(conf-router_bgp)#show conf
!
router bgp 99
neighbor AAA peer-group
neighbor AAA no shutdown
neighbor 10.155.15.2 remote-as 32
neighbor 10.155.15.2 shutdown
Dell(conf-router_bgp)#neigh 10.155.15.2 filter-list 1 in
Dell(conf-router_bgp)#ex
Dell(conf)#ip as-path access-list Eagle
Dell(config-as-path)#deny 32$
Dell(config-as-path)#ex
Dell(conf)#router bgp 99
Dell(conf-router_bgp)#neighbor AAA filter-list Eagle in
Dell(conf-router_bgp)#show conf
!
router bgp 99
neighbor AAA peer-group
neighbor AAA filter-list Eaglein
neighbor AAA no shutdown
neighbor 10.155.15.2 remote-as 32
neighbor 10.155.15.2 filter-list 1 in
neighbor 10.155.15.2 shutdown
Dell(conf-router_bgp)#ex
Dell(conf)#ex
Dell#show ip as-path-access-lists
ip as-path access-list Eagle
deny 32$
Dell#
Border Gateway Protocol IPv4 (BGPv4)
Filtering BGP Routes.
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