BGP with same AS number

[husamaga1]

Hello,

I have a kind of complicate network design, where i got 6 locations which have internet connection with the same ISP with same AS number, where every location have own router and advertises a set of IP addresses by BGP.

recently i get the 6 locations connected with fiber, so i can make 1 big network, but i want to do that periodically.

So my first location #1 (the other 5 locations are connected to location #1) will get a new 2 ISP's, and I will disconnect the old ISP I used.

My question is how to create a connectivity from location #1 to the other 5 locations without making changes to these networks (thinking about IP address, routers, switches etc...) and keep the 5 networks separated from #1 location.

Is it possible to have a BGP connectivity between these 5 locations and location #1? using the same AS number (just make a peer addresses between the routers)? or there is another solution.

Regards.

[ghostinthenet · Accepted solution]

It's possible. You need to use the following command with your ISP peering in order to allow routes from your other sites to be accepted.

neighbor x.x.x.x allowas-in 1

Obviously, this is a simplistic solution and may not apply perfectly to your scenario, but it will get around the basic rejection of paths with the same AS coming in from your ISP.

[husamaga1]

So, you want to say that I can connect every location to my location #1 with same BGP paramters and same AS number? but on my location #1 I add this line? 

[ghostinthenet]

I read that a bit too quickly.

If you're connecting your locations via the ISP and they all use the same AS, they'll all need the statement I mentioned in my previous comment. If you already have communication between them via the ISP, then this command is probably already there.

If you're connecting everything via fibre to the primary location, you can just peer with the other locations using the same AS and you'll be fine... though there are some considerations if you're redistributing BGP into an internal routing protocol.

In your current configuration, is each location seeing the networks from the other sites propagating from the ISP via BGP?

[husamaga1]

Thanks for your help, i did it and it works fine.

All my locations now, can see the ISP and internet through the ISP, and the local network see's itself. i just used the same configuration for igp and it works ok.

Regards.