[c-nsp] AS override

[Danny Vernals]

Thanks Oliver,

It is indeed risky but sadly its needed in problem I'm trying to solve:

One of our ASs has transit connectivity provided by 2 links in different
geographic locations. When the backbone between these 2 locations breaks we
have a split AS so the only way for intra-AS communication between these 2
locations is via transit (hense lcoation 1 needs routes for location 2 and
vise versa).

(Intra AS communication is normally via IGP)

(NB no route reflectors in the AS so if there is no connectivity between the
2 locations they will only announce their own prefixes to transit AS).

I'm going to lab it first to make sure no loops are caused.

Thanks

Danny

On 10/6/05, Oliver Boehmer (oboehmer) <oboehmer at cisco.com> wrote:
>
> Danny,
>
> Re-writing AS paths is a dangerous thing (as you will take BGP's only
> loop prevention mechanism away), so we are not allowing it except within
> the MPLS-VPN setup using as-override.
>
> oli
>
> Danny Vernals <mailto:danny.vernals at gmail.com> wrote on Wednesday,
> October 05, 2005 4:16 PM:
>
> > Hi Oliver,
> >
> > I just had concerns over routing table security / integrity but now I
> > think about it the same issues arise with override as with
> > allowas-in. I think I can mitigate against these issues with careful
> > design.
> >
> > Ideally I'd only like to re-write the ASN for certain prefixes that
> > are matched in a route map matching on community / prefix list etc.
> > However as far as I'm aware this is not possible?
> >
> > Thanks for the reply
> >
> > Danny
> >
> >
> > On 10/5/05, Oliver Boehmer (oboehmer) <oboehmer at cisco.com> wrote:
> >
> >
> > >
> > > Do you know of a way to configure AS override functionality
> not in
> > a > VRF? I need to allow prefixes oringated from an AS to be
> > advertised > back into it. Ideally I'd like to avoid using
> > allowas-in. I have > admin control of both of the connected
> AS's.
> >
> > as-override is, as you have observed, only available in ipv4-VRF
> > context. Why do you want to avoid allowas-in?
> >
> > oli
>