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Layer 2 over geographically disperse networks.

The situation that I am in is this:


I need to setup a DR site with a type of "flip the switch solution".  I have the solution drawn up but what I need to figure out is if I can run the same subnet at the COLO or not.  I realize this may be a really stupid question but just wanted to see if there is anyone with some insight into this.  The WAN that this will be going across is running BGP with VRF-lite.  I know this is not a lot of detail and can provide more if needed just want to see what kind of options I may have.



Bilal Nawaz

Hello, for DR, in an "Active / Standby" solution you could extend layer 2 between sites, but all depends on which type of devices you have, which technology you could get comfortable with. I could suggest L2TPv3, (example here: which is quite quick and easy to deploy. Just be mindful, of the default gateways of servers and hosts, where they would be, they'd have to be active in one place or the other depending on where hosts are based, you don't want them unnecessarily traversing a link to get to the default gateway. If switching on (albeit via shut/no shut/hsrp priority etc...) the SVI's or gateways in the DR site is part of the "flip the switch" it seems to work in my mind.

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Consider also the type of WAN you have. If the two sites are connected to an MPLS network you must carefully design the routing  to avoid load balancing between the two sites (that may deliver packet desalinated to a server in  primary site to the DR sites)  or even worst to have traffic deliverd in the DR site.

In my experience costumers that has the same LAN in primary and DR sites usually choose to have a WAN network, usually an MPLS network, to connect branches and a different link to connect the two sites. How to connect the DR to the MPLS networks depends at least on your requirements, your knowledge of BGP protocol (or the routing protocol you are using) and type of services offered by tour ISP