eBGP, iBGP, injecting networks

Sat Feb 21 00:10:48 UTC 2004

Note - I got confused by the subject and everything myself. The routes you 
have locally would not be from IBGP but just directly through IGP (i.e. 
OSPF or EIGRP etc). I don't think you can really do IBGP if routers are 
not configured with the same ASN.

On Fri, 20 Feb 2004, william(at)elan.net wrote:

> 
> Ok. The way I read this is that you're redundant as far as one of your 
> upstream links going down - it'd not cause complete meltdown as that 
> router that had that link would still be announcing that space to the 
> other router (over EBGP) and then to the net. 
> 
> What you're worrying then is what happens if actual router is down, right?
> But that begs the question of how you're getting the routes that router is 
> announcing in the first place. Is it coming from some other "edge" router
> (that is also talking over local net to your 2nd core router)? 
> 
> If so each of your routers has complete local routes table through IBGP 
> and you are not announcing it all because you're using static "network" 
> statements in BGP config. In that case my suggestion would be to drop EBGP 
> connection between routers and have each router announce entire ip space 
> but put up 'as-path prepend' statements with the other adding the other 
> router's ASN for routes that you want to be considered as being primary 
> from that other router. Now exact configuration suggestion would depend on 
> what hardware the routers are, i.e. is it cisco, etc. 
> 
> P.S. I've never been in situation of having to merge two ASN's or in situation
> you describe, so possibly people who have would have better suggestions. 
> 
> On Fri, 20 Feb 2004 isaac at ravengate.net wrote:
> 
> > 
> > greetings list,
> > 
> > hoping someone can hook me up on the right way to do this.    
> > 
> > ---
> > 
> > we have two ASN's we control.
> > 
> > we have two border/edge routers (1 in each ASN) that talks to a
> > different backbone provider.
> > 
> > the two border routers peer with eachother over eBGP and also are in
> > the same OSPF process.  (we are working to merge them into the same
> > BGP ASN)
> > 
> > my question is this:
> > 
> > how do we achieve router redundancy between these two routers?
> > 
> > currently if we lose a transit link, the traffic will flow fine out
> > the other pipe.
> > 
> > but we don't have BGP network statements in router 2 that exist in
> > router 1 and we don't have BGP network statements in router 1 that
> > exist in router 2.
> > 
> > so the routes injected into BGP from router 1 will get withdrawn right
> > if router 1 dies?
> > 
> > is it a problem to announce the same networks from two different eBGP
> > peers to two different upstreams?
> > 
> > ------
> > 
> > if you are still reading, thanks!
> > 
> > to clearify some more-
> > 
> > current setup:
> > 
> > current setup:
> > 
> > ASN 1 (we're not Genu!ty- just using for an example)
> > 
> > :)
> > 
> > ASN 1 injects all of its own space and announces this space to
> > Above.net and ASN 2
> > 
> > ASN 2 injects all of its own space and announces this space to Savvis
> > and ASN 1.
> > 
> > so stuff out on the net looks like:
> > 
> > 1 6461 etc etc
> > 
> > and
> > 
> > 1 2 6347
> > 
> > -------
> > 
> > 2 6347 etc etc
> > 
> > and
> > 
> > 2 1 6461 etc etc
> > 
> > -------
> > 
> > so, you see we are prepending on of our AS's on the way out.
> > 
> > the problem is tho, we only have 1 router in each respective Autonmous
> > System injecting address space.  if we lose that router, we lose
> > announcing that ASN's space.
> > 
> > is it totally going to cause probs to have routes originating from two
> > different AS's?  routing loops would be a real drag.
> > 
> > what about having an iBGP router in AS 1 inject the same space as the
> > border router in AS 1?  this other router also peers with AS 2....
> > 
> > thanks a lot!
> > jg