From: CCIEin2006 (ciscocciein2006@gmail.com)
Date: Mon Jan 09 2006 - 16:47:08 GMT-3
Hello Marvin,
What constitutes "behind the local-as". Do you mean a confederation or do
you mean another ebgp peer?
In the case of ebgp peer isn't it all relative i.e. from the perspective of
R1, R4 is behind AS23?
On 1/9/06, Marvin Greenlee <marvingreenlee@yahoo.com> wrote:
>
> 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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>
>
>
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