From: George Cassels (glcassels3@nc.rr.com)
Date: Fri Jun 24 2005 - 17:02:42 GMT-3
Actually no it does not look right it will send routes that pass ASpath
acl 1 and receive routes that pass aspath acl 2 from neigh 193.1.12.10.
I have another question though. I did a lab today which wanted me to
only allow routes that came through or originated from AS 1. When I did
the AS path ACL I did
Ip as-path access-list 1 permit _1_
And under BGP I did
Router bgp X
Neigh x.x.x.x filter-list 1 in
The funny thing was that this is allowed all routes in. I then put the
aspath acl in a route-map and applied the route-map to the neighbor
inbound and it worked because there was only one seq in the route-map so
everything else was denied. My question though is are as-path ACLs like
IP based ACLs with a deny at the end of the list?
I noticed in the example from the cisco site that they show an example
with only deny statements, but say it will only block the AS's in the
list and not all.
See below
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/
iprrp_r/ip2_i1g.htm#wp1036594
Examples
The following example creates autonomous-system path access list (number
500) that specifies that the BGP neighbor with IP address 10.125.1.1 is
not to be sent advertisements about any path through or from the
adjacent autonomous system 123:
ip as-path access-list 500 deny _123_
ip as-path access-list 500 deny ^123$
router bgp 109
network 10.108.0.0
neighbor 10.140.6.6 remote-as 123
neighbor 10.125.1.1 remote-as 47
neighbor 10.125.1.1 filter-list 1 out
George
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Rasal Abdul Kader
Sent: Friday, June 24, 2005 12:42 PM
To: Cisco certification
Subject: BGP AS path filtering - DOC CD example
Could someone tell if the below is correct. I got it from the DOC CD
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fipr_c/ipcprt2/1cfbgp.htm#wp1002924
--------------------------------------------------------
The following example shows BGP path filtering by neighbor. Only the
routes that pass autonomous system path access list 2 will be sent to
193.1.12.10. Similarly, only routes passing access list 3 will be
accepted from 193.1.12.10.
router bgp 200
neighbor 193.1.12.10 remote-as 100
neighbor 193.1.12.10 filter-list 1 out
neighbor 193.1.12.10 filter-list 2 in
ip as-path access-list 1 permit _109_
ip as-path access-list 2 permit _200$
ip as-path access-list 2 permit ^100$
ip as-path access-list 3 deny _690$
ip as-path access-list 3 permit .*
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