I have a situation that we're trying to figure out. What's been requested is that we have a way of mirroring our VM servers from our corporate site to the DR site. They want to keep the same subnets that we have at corporate, and be able to use these at the DR site.
I've thought about L2TPv3, but that's not going to help with the subnets (your thoughts?). I believe this is going to be impossible to do. How do you handle remote site DR?
Okay, here is what you could do.
You could address the servers in your DR site as 192.168.1.0. For the replication you could NAT the DR servers to 192.168.2.0 so the DC servers could access them - note you would need to make sure that NAT does not break the replication.
Then you advertise out the 192.168.1.0/24 network from both the DC and the DR site. But you make sure that you use a BGP MED so that in ordinary operation all traffic for 192.168.1.0 would go to the DC servers. If the DC connection failed then the remote sites would then route to the DR site using the same 192.168.1.x addresses.
I'm not trying to make this sound easy as it would need testing and you also have to decide whether you want to failover automatically if the DC link goes down ie. what if there is just a short blip and you have fallen over to the DR - this can create more problems than it solves.
So sometimes automatic DR is not what is needed. It really does depend on the amount of downtime the client can handle.
GSS is a cleaner solution but if all the clients use IP addresses to access the servers then it is very little use to you.
The other thing is what are you trying to DR for - ie. the above in terms of BGP only works for a DC site failure whereas the GSS can handle individual server failures.
As you can probably see this is a huge subject :-)