iBGP question.

I have found there is something like: neighbour allowas-in in cisco's BGP configuration.

Now, the question is what is better?:

1. use neighbour allowas-in
2. use iBGP multihop option
3. (if possible) use some tunnel to interconnect routers within the same AS

Regards, Jarek

you need to have a full mesh - for example you could use route rflection fron either A or B to C

If possible- use full mesh. If not -use other techiques- like route reflector or confederation.

OK, but is it possible to implement full mesh using tunnels over Internet (or iBGB multihop?) or this must be direct link between routers?

Jarekj

As long as you have a route at the existing routers which enables you to reach the third iBGP neighbor, and that new iBGP neighbor has a route back to your 2 existing routers, you can peer up with that new (third) router.

No direct connection, or dedicated facility is needed to do this. All three routers need to have routes / reachability with each other, that's all. And yes, full mesh should be used - or - route reflection.

message

A more fundamental question - why do you need to run BGP to existing site ?

Do you not just need to run an IGP (via GRE tunnel( for inter-AS traffic ?

It is not clear why one would want to use iBGP to other sites in this case.

Can understand an IGP via GRE tunnels to reach internal resouces

message

I have 2 locations (2 routers BGP using the same AS): A and B. On each site I have separate BGP upstream links to at least 2 peers (on each site), so in fact, those routers are using the same AS but are announcing different prefixes. I just have done my internal assignement: prefix X is used in location A, and prefix Y in B.

It's done this way to provide my customers Internet using my PI adresses on each location. Now, because routers A and B use the same AS, so, I need iBGP session to reach prefix X (announced by A) from B, and vice versa. My AS is'nt big enough to make some internal traffic policy so I just need some way to reach my prefixes between sites. Unfortunetly, I have very poor direct leased link between those sites.

I have to change it, and I am thinking of alternative solutins, for example:

- make iBGP session between A and B using GRE over Internet (if possible)

- use allowas-in to receive prefix X on router B through foreign peers (normaly BGP blocks prefikses originated from own AS).

I don't know if my english is precise enough but I tried to explain situation as good as I can. The question is: "what solution is better?"

Regards, Jarek