North American Network Operators Group
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Re: Peering best practices advice needed.

  • From: Graham Blake
  • Date: Wed Dec 08 13:49:14 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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