Routing

[Siddique]

Dear ALL,

Hope you are well.

ISP Company ABC buy a new another ISP company named XYZ. Now management want to connect both network into one. ISP ABC running OSPF , BGP and MPLS and ISP XYZ  Running ISIS , BGP and MPLS. Now how we connect this 2 network domain. Please I need all of yours help in this regards.

Q1. What is the best solution to interconnect this 2 networks.

Q2. Please mention what configuration do I need to change/Edit or Add into  OSPF, ISIS, BGP and MPLS configuration to interconnect this 2 networks.

Thanks

ABSeddeeq

[Thomas Schmitt]

there are a lot of possibilities, how to achive it and there isn't a best way.

But from very high level, without details, I would at first connect two ISPs with CsC option B or C, if both have BGP RRs (https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_ias_and_csc/configuration/15-s/mp-ias-and-csc-15-s-book/mp-vpns-ebgp-multipath-csc-ias.html). Actually you can stop at this point, but if you want to proceed, you have a lot of options.

You have to decide, what you want to use in the feature - OSPF or IS-IS and then extend your choice to second network. Or you can configure unified (seamless) MPLS and don't change IGP. If you choose seamless MPLS, you can implement segment routing.

There is 1 billion factors, that you have to take into account, if you are going to merge ISP networks and I estimate, only 10% of them relate to technical issues, 40% is about management (lead, cost, legal regulations), 25% relay to  staff and another 25% relate to geographical location (+infrastructure)

[MHM Cisco World]

for me best is using Inter-AS between two ISP.

[Joseph W. Doherty]

Any overlapping IP address space?