[c-nsp] BGP Route Nailing & Reoriginatin

[Shakeel Ahmad]

Umm i would do it like this  --- Two options (idealy i would go with second
but not sure what your requirment is)

* Concidering you want BGP still running between R1 & R2

Use Conferdeation in between R1 & R2 with AS2 as Confederation Identifier so
that AS3 only knows about AS2 (two private AS can be used on R1 & R2 to hide
in AS2 identifer) .. Solves your issue !!!

* Concidering we don't want (or should'ny) run BGP in between R1 & R2

on R2/AS2 put static routes for 1.1.1.0/24 & 2.2.2.0/24 towards R1 (There's
no point of BGP running in between R1 & R2 in this case). Now in your BGP
session at R2, advertise 1.1.1/24 & 2.2.2/24 via network statement. It'll
solve the first issue.....and R3 will recieve 1.1.1/24 & 2.2.2/24 as
originated by AS2 -


now points come to stop flapping , simply (also a best practice for both
above) put these static routes on R2/AS2

ip route 1.1.1.0/24 Null 0 250
ip route 2.2.2.0/24 Null 0 250

Remmember metric should be as lowest as possible and the subnet thrown on
Null 0 should be as aggregated as possible. This will eventaully stop your
flaps and routes will never disappear from AS3 and will always point back to
AS2.


hope this helps....

Shakeel Ahmad


On 12/5/06, Lawrence Wong <lawrencewong72 at yahoo.com> wrote:
>
> Dear gurus,
>
> I have an environment as follows:
>
>        (R1 / AS1) <-> (R2 / AS2) <-> (R3 / AS3)
>
>
> R1 (router 1) has AS number 1 (AS 1) and advertises the routes 1.1.1.0/24and
> 2.2.2.0/24 to R2 which inturn advertises to R3. All advertisement is done
> via eBGP.
>
> Is it possible to configure R2 such that the routes 1.1.1.0/24 and
> 2.2.2.0/24 are advertised to R3 under AS2 instead of AS1? At the same
> time, can R2 "nail" down the routes so that in the event the (physical &
> BGP) link between R1 and R2 is down, the route continues to be advertised to
> R3 (and under AS2)?
>
> The objective is to "hide" AS1 and also to prevent BGP dampening at R3
> caused by flapping link between R1 & R2.
>
>
> TIA!
>
>
>
>
>
>
>
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