We already have BGP implemented (ISP redundancy) at the main office building. It's got its ARIN approved ASN and a /24 prefix announced to the upstream ISPs.
My question is that if we were going to implement BGP at a branch office, do we need to apply a new AS number? Will it be a brand new setup or we can somehow use the same ASN? The branch office has its own /24 prefix and Internet connection. It talks to the main office through a L2L VPN tunnel.
If we can use the same ASN, what are the special configurations we need to be aware of? Thanks in advance.
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It is not requried or mandatory .
You can use same AS number for all locaiton ie. IBGP over SP network.
You can use same ANS number but for that you need to have a word with your SP , SP provider need to configure for that one.
SP need to configure an extra command for Branch locations under Address-Family.
i.e neighbor x.x.x.x as-override
Assuming iBGP peers need to be fully meshed and they need to be able to reach each other through either IGP or EGP network. We can implement Route-reflector or Confederation but how do we do that across public IP space WAN?
How many routers do you require to run IBGP on a single site?
As a side note, BGP route-reflector and confederations needs only IP reachability between routers, as long as you have IP reachability you can configure either one.
BGP router-reflector and Confederations reduces the number of TCP sessions required by fully meshed IBGP and disables the Split Horizon rule in BGP.
I have two routers running BGP on each side. I am sure we can do route-reflector or confederation to make iBGP working. However I am concerned about peering iBGP across multiple hops over the Internet. The hello packet is sent every 60 seconds by default. I just wanted to make sure this is the best practice and commonly deployed in the field.