From: Marvin Greenlee (marvingreenlee@yahoo.com)
Date: Mon Jan 09 2006 - 13:54:04 GMT-3
No-prepend example from another message board:
...
'no-prepend' prevents the 'local-as' AS from being
added to the path, but only for peerings "behind" the
'local-as' peering. From the outside, you will always
see the 'local-as'.
****
R1(AS1)--R2(AS23)--R3(AS23)--R4(AS4)--R5(AS5)
Network XX on R1, Network YY on R5.
Assuming that R3's peering to R4 includes local-as 100
R1(AS1)--R2(AS23)--R3(AS23)--local-AS100))-R4(AS4)--R5(AS5)
R1 sees network YY with path 23 100 4 5.
with no-prepend on R3's peering to R4, R1 would see 23
4 5.
R5 sees network XX with path 4 100 23 1.
with no-prepend on R3's peering to R4, R5 still sees
the path as 4 100 23 1.
****
In this case, R1 and R2 are "behind the 'local-as'",
and may or not see the local-as in the path depending
on whether or not the no-prepend keyword is used. R4
and R5 are "outside the 'local-as'", and will always
see local-as, regardless of whether or not R3 is
configured with the 'no-prepend' keyword.
--- Victor Cappuccio <cvictor@protokolgroup.com>
wrote:
> Hello List..
>
>
>
> On
>
<http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/ipr
> rp_r/ip2_n1g.htm#wp1037846>
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/iprr
> p_r/ip2_n1g.htm#wp1037846
>
> We can find the description for what is used the
> local-as option in BGP,
>
>
>
>
> no-prepend
>
> (Optional) Configures the router to not prepend the
> local autonomous system
> number to any routes received from an external peer.
>
>
>
>
> Is this correct?
>
> IMHO, I believe that this should be read like:
> Configures the router to not
> prepend the local autonomous system number to any
> routes advertised to
> external peers
>
>
>
> Is this correct or I have a misunderstanding of the
> concept?
>
> Thanks
>
> Victor.
>
>
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