From: Aidan Marks (amarks@cisco.com)
Date: Fri Jan 03 2003 - 08:33:04 GMT-3
Not sure what else you need to know, but here is something - have not
checked CCO for this, perhaps it's in the 12.0S stuff somewhere back around
12.0(2.6)S when it was implemented.
Aidan
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bgp enforce-first-as
To have cisco IOS enforce the first AS (in the AS_PATH) of a route
received from an eBGP peer to be the same as the remote AS configured, use
the 'bgp enforce-first-as' command. To not enforce this rule, use the
'no' form of the command.
bgp enforce-first-as
no bgp enforce-first-as
Syntax Description
This command has no arguments or keywords.
Default
The software does not require the first AS (in the AS_PATH) of a route
received from an eBGP peer to be the same as the remote AS configured.
Command Mode
Router configuration mode.
Usage Guidelines
This command first appeared in Cisco IOS Release 12.0S.
If 'bgp enforce-first-as' is enabled then any update (received from an
eBGP neighbor) that does not have the neighbor's configured AS at the
beginning of the AS_PATH will be denied. When configured, the command
applies to all the eBGP peers of the router.
Example
The following example shows a configuration in which all incoming updates
from the eBGP peers will be examined to guarantee that the first AS (in
the AS_PATH) is in fact the same as the configured AS for that neighbor.
!
router bgp 109
bgp enforce-first-as
neighbor 131.108.1.1 remote-as 65001
neighbor 160.89.2.33 remote-as 2051
!
Related Commands
show ip bgp
At 05:04 PM 3/01/2003, cebuano wrote:
>Hi all.
>I can't find any info on this command. Any help is greatly appreciated.
>As per CCO.
>* If you enabled bgp enforce-first-as and the UPDATE doesn't
>contain the AS of the neighbor as the first AS number in the
>AS_SEQUENCE, the router sends a notification and closes the session.
>Thanks.
>Elmer
>.
.
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