Dell Force10 C150 Configuration Manual page 243

Filter on an AS-Path attribute
The BGP attribute, AS_PATH, can be used to manipulate routing policies. The AS_PATH attribute
contains a sequence of AS numbers representing the route's path. As the route traverses an Autonomous
System, the AS number is prepended to the route. You can manipulate routes based on their AS_PATH to
affect interdomain routing. By identifying certain AS numbers in the AS_PATH, you can permit or deny
routes based on the number in its AS_PATH.
To view all BGP path attributes in the BGP database, use the
Privilege mode (Figure
Figure 10-26. Command example: show ip bgp paths
FTOS#show ip bgp paths
Total 30655 Paths
Address Hash Refcount Metric Path
0x4014154
0x4013914
0x5166d6c
0x5e62df4
0x3a1814c
0x567ea9c
0x6cc1294
0x6cc18d4
0x5982e44
0x67d4a14
0x559972c
0x59cd3b4
0x7128114
0x536a914
0x2ffe884
0x2ff7284
0x2ff7ec4
0x2ff8544
0x736c144
0x3b8d224
0x5eb1e44
0x5cd891c
--More--
AS-PATH ACLs use regular expressions to search AS_PATH values. AS-PATH ACLs have an "implicit
deny." This means that routes that do not meet a deny or match filter are dropped.
Use these commands in the following sequence, starting in the CONFIGURATION mode to configure an
AS-PATH ACL to filter a specific AS_PATH value.
Step Command Syntax
ip as-path access-list
1
as-path-name
10-26).
0 3 18508 701 3549 19421 i
0 3 18508 701 7018 14990 i
0 3 18508 209 4637 1221 9249 9249 i
0 2 18508 701 17302 i
0 26 18508 209 22291 i
0 75 18508 209 3356 2529 i
0 2 18508 209 1239 19265 i
0 1 18508 701 2914 4713 17935 i
0 162 18508 209 i
0 2 18508 701 19878 ?
0 31 18508 209 18756 i
0 2 18508 209 7018 15227 i
0 10 18508 209 3356 13845 i
0 3 18508 209 701 6347 7781 i
0 1 18508 701 3561 9116 21350 i
0 99 18508 701 1239 577 855 ?
0 4 18508 209 3561 4755 17426 i
0 3 18508 701 5743 2648 i
0 1 18508 701 209 568 721 1494 i
0 10 18508 209 701 2019 i
0 1 18508 701 8584 16158 i
0 9 18508 209 6453 4759 i
Command Mode
CONFIGURATION
show ip bgp paths
Purpose
Assign a name to a AS-PATH ACL and enter AS-PATH
ACL mode.
Border Gateway Protocol IPv4 (BGPv4) | 243
command in EXEC