[c-nsp] BGP - Multihop across igp network

[Paul Stewart]

I just wanted to say thanks to everyone who replied to this issue - it's
resolved now.  We ended up deploying iBGP across the 6500's today and the
customer is running and quite happy...;)  We did run full tables which
worked out ok as well....

Cheers,

Paul


-----Original Message-----
From: Sascha E. Pollok [mailto:nsp-list at pollok.net] 
Sent: April-06-10 12:34 PM
To: Paul Stewart
Cc: cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] BGP - Multihop across igp network

Hello Paul,

> We have the capability to bring up iBGP on the 6500's which we might
examine
> (just never needed to).  I think it's safe to assume in our environment
that
> if we brought up full tables on the 6500's using iBGP that there is no
need
> to redistribute anything into OSPF as they will become aware of the route
> anyways.

we still have a few very old boxes with little memory and
some funky leased lines connected to that
also participate in iBGP to learn some customer routes
(<100). Works like a charm. I would strongly vote to this
way but if you do not ...

> If we didn't do that, would it be best to redistribute on the 7600's (EBGP
> to OSPF) or would it be better at the 3825 side of things (which we manage
> and have full control over - it participates in OSPF as well)?  I'm
thinking
> it would make more sense at the 3825 side?

I'd build the tree from the center (7600s) and set up
redistribution (or iBGP stuff) from there. Let the relevant
access routers get to know about the routes from where the
routes are originally learned through eBGP.

But thats just my way of doing it.

Good luck!
Sascha

> -----Original Message-----
> From: Sascha E. Pollok [mailto:nsp-list at pollok.net]
> Sent: Tuesday, April 06, 2010 11:03 AM
> To: Paul Stewart
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] BGP - Multihop across igp network
>
> Hello Paul,
>
>> Connected to these 7600's we have a pair of 6500's not doing BGP (however
>> participating in OSPF as all our boxes do)
>>
>> Connected off one of the 6500's we have a 3825 at a customer site
>>
>> The customer who is connected to a 3825 wants a full BGP feed from us.
>>
>> So, I created a pair of ebgp-multihop sessions between the 3825 and our
> two
>> 7600's - both tables populated and everything looked good.  Once the
>> customer brought up their session all the traffic seems to loop between
> our
>> networks.. Almost like a blackhole effect.  In our 7600's I can see the
>> customer routes advertising out and BGP itself looks correct when I do a
>> "show ip bgp xxxxx" towards one of their netblocks.
>
> Your other routers need to know about the customer's network.
> You can either redistribute the customer's EBGP prefixes
> into OSPF (selectively using e.g. route-maps on the 7600's)
> or talk BGP to your other routes but learn only the customer's
> routes. We are doing a similar thing. We are tagging customer-learned
> routes with a BGP community and announce only prefixes carrying
> this community via IBGP to the access routes.
>
> Thus, the access routers carry only a few prefixes and can perfectly
> route towards the customer.
>
> Sascha
>
>

-- 
Sascha E. Pollok                     E-Mail: sp at iphh.net
Leiter Netzwerkdesign und -betrieb   Tel: +49 (0)40 374919-10
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