Multihoming with 2 different ISPs to two separate routers with different AS numbers

[cargostud]

I've inherited a network with my new job.  The routing is working but I'll describe the topology and then ask my question...

I have two different ISP WAN circuits. (Thus two different AS numbers)

I have two core routers connected to the respective ISPs and each router has a different AS number. (I see most designs having both routers in a single AS)

BGP from first router is peered with its respective ISP AS number and with the other Core Router AS

BGP from second router is peered with its respective ISP AS number and with the other Core Router AS

Show IP BGP route shows routes and none of them appear to be iBGP.

Is the fact that both core routers have different AS numbers causing everything to be eBGP?

[paul driver]

Hello

The design you have describe isn't uncommon.

Do the two site routers have the same bgp ASN number ?
They could be interconnected via an IGP such as ospf /eigrp or even rip instead of ibgp, Anyhow....Whats your question?

res
Paul

[casanavep]

Can I just verify that your ASN is the same for both routers, one belonging to your company, but the two routers each peer with unique ISP ASNs?  

[cargostud]

Hi Paul.  Both of my on site routers each have different BGP AS numbers.   I just wanted to verify that this design is not out of order with what should be done.  I can also confirm that there is an OSPF area that includes my two routers. 

The main reason for this inquiry was to verify that I am running eBGP and not iBGP.  My company is looking to implement some new SD-WAN devices that are not able to pass iBGP routes but will work fine with eBGP.   

[Richard Burts]

The fact that your on site routers and core routers have different AS numbers is indeed the reason why your routes show up as EBGP and not IBGP. Your implementation is not a common one. But I would not say that it was out of order.

I do not know enough about your environment to say anything meaningful about the changes that you are planning for SD-WAN. If these new devices will not pass IBGP then it means that they do not want to be placed between routers running BGP for the enterprise to two external peers. And that is just what you are about to do. I would approach this with caution.

HTH

Rick

[cargostud · Accepted solution]

Thanks Rick. Indeed, I'm approaching with caution. The SD-WAN device will be going between the two core routers at the Data Center. It's a good thing the two core routers already have different AS numbers. It can't handle iBGP so it has to be eBGP. I've discovering hidden gems in the configs over the past few days. This will be thoroughly planned out before we do the cut over.