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838
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ip as-path

wgranada1
Level 1
Level 1

I was looking over a router config when I ran across the following:

ip as-path access-list 17 permit ^[0-9]+$

ip as-path access-list 17 permit ^$

what is the meaning of this I tried looking it up but maybe I'm not understanding what I read....sorry for the silly question

Thank you warren

4 Replies 4

Collin Clark
VIP Alumni
VIP Alumni

Warren-

Not a silly question! I won't give you the answer directly, but take a look here to figure it out.

http://www.cisco.com/warp/public/459/bgp-toc.html#asregexp

What you see are regular expressions that are used to filter AS's in BGP.

HTH and please rate.

cisconoobie
Level 2
Level 2

(ip as-path access-list 17 permit ^$) is used for bgp updates sent to peers.

There should be a router bgp route-map associated with this.

Means all networks originating from your AS and no others, protects your AS from becomming a transit-as.

The other command, I'm not exactly sure, have to do the math.

Haris P
Level 4
Level 4

Hi,

the statement ^[0-9]+$ will match bgp routes originated from next upstream ....that's with AS-path length 1 , the next statement ^$ is will match the routes originated by the router... So The as-path 17 will be a summary of routes originated from next upstream and routes originated by the router

Regards,

Haris

Thank you all for the info it was very helpfull and thank you Haris for the explaination!!!

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