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Ivan Ostreš 02-19-2005 04:12 PM

Interesting BGP peering
 

Hello all,

I've been doing a VPN trough ADSL network and found out something
interesting (still not sure what's really going on).

I have a thing like this:

RTR1751----ADSL-----ISP-----PIX515----C2621XM

I'm running IPSec between RTR1751 and PIX515. Trough that VPN, I'm
driving BGP - not for real routing, just as a mechanism that brings up
VPN when address on ADSL changes and for the times when ADSL is dead, to
bring up ISDN backup.

RTR1751 has a default route to its dialer interface (PPPoE) and it has
defined loopback as BGP peer-point. I can ping (using loopback as source
address) loopback on C2621XM.

The thing is that when using BGP, connection won't come up (I've set
update-source and multihop feature). Debug says something like "...no
route to destination / delaying OPEN message for xxxxx ms".

When I add a host route (/32) on RTR1751 for C2621XM loopback,
everything works fine.

So, the final question is why ping works using just default route
(loopback to loopback) while BGP won't send OPEN message (loopback to
loopback) without /32 route for BGP endpoint?

Anyone knows why?

--
-Ivan.

*** Use Rot13 to see my eMail address ***

Brant I. Stevens 02-19-2005 11:45 PM

Re: Interesting BGP peering
 
eBGP must have a route in its table for peering with its neighbor; a default
is not going to do.

As for why,... normally, an eBGP peer must be off of a directly-connected
interface. (Stability is my guess why this was done). EBGP multi-hop is a
"hack" designed to get around that.

Is your /32 route referencing the physical interface?

On 02/19/2005 11:12 AM, in article
MPG.1c8183da32ab87ea989817@news.individual.net, "Ivan Ostreš"
<vina.bfgerf@mt.ugarg.ue> wrote:

>
> Hello all,
>
> I've been doing a VPN trough ADSL network and found out something
> interesting (still not sure what's really going on).
>
> I have a thing like this:
>
> RTR1751----ADSL-----ISP-----PIX515----C2621XM
>
> I'm running IPSec between RTR1751 and PIX515. Trough that VPN, I'm
> driving BGP - not for real routing, just as a mechanism that brings up
> VPN when address on ADSL changes and for the times when ADSL is dead, to
> bring up ISDN backup.
>
> RTR1751 has a default route to its dialer interface (PPPoE) and it has
> defined loopback as BGP peer-point. I can ping (using loopback as source
> address) loopback on C2621XM.
>
> The thing is that when using BGP, connection won't come up (I've set
> update-source and multihop feature). Debug says something like "...no
> route to destination / delaying OPEN message for xxxxx ms".
>
> When I add a host route (/32) on RTR1751 for C2621XM loopback,
> everything works fine.
>
> So, the final question is why ping works using just default route
> (loopback to loopback) while BGP won't send OPEN message (loopback to
> loopback) without /32 route for BGP endpoint?
>
> Anyone knows why?



Ivan Ostreš 02-20-2005 09:39 AM

Re: Interesting BGP peering
 
In article <BE3D39FE.51BAA%branto@branto.com>, branto@branto.com says...
> eBGP must have a route in its table for peering with its neighbor; a default
> is not going to do.
>


This could be a good explanation. Any references to some materials that
would support your saying?

> Is your /32 route referencing the physical interface?
>


No. It's refering to loopback interface of another router.

--
-Ivan.

*** Use Rot13 to see my eMail address ***

JNCIP#0136 02-22-2005 08:19 PM

Re: Interesting BGP peering
 
Here You go (You may need to scroll down a bit)
http://www.cisco.com/warp/public/459/24.html#noroutes
HTH,
Cheers
Alex

"Ivan Ostre " <vina.bfgerf@mt.ugarg.ue> wrote in message
news:MPG.1c82794e9750261098981b@news.individual.ne t...
> In article <BE3D39FE.51BAA%branto@branto.com>, branto@branto.com says...
> > eBGP must have a route in its table for peering with its neighbor; a

default
> > is not going to do.
> >

>
> This could be a good explanation. Any references to some materials that
> would support your saying?
>
> > Is your /32 route referencing the physical interface?
> >

>
> No. It's refering to loopback interface of another router.
>
> --
> -Ivan.
>
> *** Use Rot13 to see my eMail address ***




Ivan Ostreš 02-22-2005 08:44 PM

Re: Interesting BGP peering
 
In article <cvg3qn$1sq$1@newstree.wise.edt.ericsson.se>, none@nospam.org
says...
> Here You go (You may need to scroll down a bit)
> http://www.cisco.com/warp/public/459/24.html#noroutes
>


Thanks Alex, that's exactly what was happening and I fixed it the same
way as suggested (I feel like I've reinvented hot water).

--
-Ivan.

*** Use Rot13 to see my eMail address ***


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