New Data Center with same AS Number

[johnnylingo]

I'll be bringing up a new data center next month, independent Internet connection with different ISP than the old one.  The old and new data centers will have a private Layer 2 link between the two core switches.

My question is how to handle BGP on the border routers.  If re-use the same AS Number (which I'd like to), the old data center will ignore the new data center's originating prefixes and vice-versa due to seeing it's own AS on an external route.  Some work-arounds I can think of are:

1) Configure GRE tunnels between the border routers and then iBGP

2) Run iBGP on the core routers, then use route-reflectors to avoid full mesh complications

3) Connect the border routers to the cores on a private vlan, then utilize the inter-data center L2 link

4) Use a separate AS Number

5) Configure BGP confederation, which the old and new data centers as separate "states"

While I think any of these would work, I can think of multiple pros and cons.  Is there a best practice, or any work experience someone would care to contribute?  I'm all ears.

[johnnylingo]

Found this talk which mentions GRE Tunneling and just using a different ASN.

https://supportforums.cisco.com/message/3483950#3483950

Any thoughts on the other options?

[Shirshendu Nandi]

Why you need your Old DC need to learn your new DC prefixes Via BGP . You can redistribute your internal prefixes to IGP ( preferably Via tagging ) so that reaching the new Prefixes will be preffered via  IGP

BTW whats the IGP running between these DC

Preferably create and /30 over between your DC over the L2 network and run OSPF between them

You should consider redundancy option for your internet as and when when one of your DC internet is going down the traffic passes over the other DC,

To Acheive this IBGP will be a great option to look forward and Run between your DC. Just you nee to play around local preference of your prfefixes /default route

[johnnylingo]

Security.  Any request to an external IP should be routed out via the firewall.  So there is a requirement for the border teir to have routing. 

[Shirshendu Nandi]

Pls provide diagram of your set Up  indicating all components  FW routers etc( both old and new) with .Any Solution would be incomplete without exact set up  knowledge

[johnnylingo]

Pretty simple setup - 6500/VSS at the core, 6503s at the border, and ASA5585 firewalls (single context, Active/Standby)

http://2.bp.blogspot.com/-fORAeni6StE/USQlZ-zzYVI/AAAAAAAAA6I/75eapFjW6Bg/s1600/Data_Center_BGP_Design.png

OSPF can certainly be configured on the private leased line, however since the cores are 6500/VSS, iBGP could be used as well. 

[Shirshendu Nandi]

Yes IBGP is the best Option in this scenario in the border routers for internal prefixes reachability.