Peering best practices advice needed.

Wed Dec 8 18:45:23 UTC 2004

Hi there,
If I understand your predicament correctly, our company has a similar 
situation. We have two locations from which we need to advertise routes 
from our AS, but our internal link between these two locations is a very 
high cost satellite link. This means we can not afford to advertise our 
whole IP allocation equally from both locations.

We have a /19 allocated, and we advertise both the /19 from each location, 
and the more specific /20 particular to each location. To circumvent the 
loop detection, we use the hidden Cisco command, neighbour x.x.x.x allow-as 
in. This allows each location to accept the remote's advertised /20 to be 
inserted into the routing table. Should connectivity ever be lost across 
the public networks in between, there is a higher cost static route over 
the satellite link.

Perhaps in a more complex and more meshed AS, this loop dodging would be a 
bad thing(tm). In our simple two location, semi-discontiguous network 
layout, it has been a problem-free solution. Hope this helps in some way.
Regards,
Graham Blake
SSI Micro Network Services

At 10:03 AM 08/12/2004, Rolo Tomassi wrote:

>Hi all,
>
>Please forgive the simplistic nature of the query..
>
>Basically my company is multi-homed with 2 different providers in the UK, 
>and advertising a /18. Now some colleaguges in another part of the world 
>want to break that /18 into two /19's and advertise one /19 and we 
>advertise the other. This is fine, however we are NOT running IBGP in the 
>core, therefore the UK customers in the /19 will not be able to reach the 
>other /19 as there would be a loop detected through EBGP.
>
>Now someone mentioned that we could use AS-LOOP-IN feature which will 
>overcome this problem and allow us to route to each other via EBGP. I 
>really think this is a bad idea but until we get an internal link - I dont 
>see a way forward. So... anyone doing this currently in their network or 
>have any "best practices" way round this. I want our company to be good 
>Netizens but still be able to pass traffic between the 2 /19's.
>
>Any help would be greatly appreciated.
>
>Rolo !
>
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