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BGP multi-site active/standby in one ASN?

Proposing a design to connect two DCs running active/standby to a single Internet Service Provider (one ISP to start with, more to come) is it possible or even advisable to use one ASN across both sites or is it better to have an ASN dedicated per site?

The backend of the two sites are already Layer2 connected across the core only (not at the internet edge) for tasks like SAN replication with limited IP connectivity allowed.

In the core there is already a Service Provider internal WAN edge coming into each of the two sites. This SP WAN edge already runs an existing BGP with a private ASN per site. These two ASNs are connected over a backend L2 link with eBGP for a secondary path only - primary inter-site path is via the Service Provider networks. It is a completely collapsed core, no IGP just two seperate iBGPs running "redist connected" with HSRP linked by a standby backend eBGP.

So...

1. Can/should the new Internet edges use a single ASN?

2. What's the best way to interconnect the proposed new internet edges today. Given that an internal re-design of the core introducing at least an internal access layer and an IGP will be upcoming

Thanks in advance

1 REPLY
Bronze

Re: BGP multi-site active/standby in one ASN?

As you are planning to come up internal redesign & implemeting an IGP, you can go for single ASN. Make sure you use the BGP attribute, MED, to play a pivotal role while communicating with the SP (http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094934.shtml).

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