[c-nsp] GRE tunnel to do span vlan across two datacenters?

[Lamar Owen]

On Wednesday, July 06, 2011 12:08:53 PM Jason Gurtz wrote:
> A firm has proposed creating a GRE tunnel between two datacenters (using a
> 3750X stack at each) to create the spanned vlans needed for VMWare
> failover application.

> Clearly there is tunnel overhead but I sense there are other failure modes
> here that aren't so clear to me--I am familiar in concept with GRE tunnels
> but don't have a heck of a lot of opex. Can anyone share more insight on
> the merit (or lack of) with this proposed design? I am aware (via this
> list, thanks!) of several shortcomings surrounding 3750 based stacks, but
> cisco alternatives seem pricier still or too big. There is dark fiber
> available, what about VPLS w/ LDP or L2TP solution?

L2TPv3 is what you want if you want tunneled.

I have done VMware ESX vMotion et al over a bridged GRE tunnel (using RSFC's in Catalyst 5505 switches to terminate the bridged tunnel) and while it works it ain't pretty.  The piece that was least pretty was all the broadcast traffic traversing the bridging.....

In our case, the reason we did this was due to the WAN link being PoS on OC3, with L3 only OC3 interfaces on GSR.

Several others have already detailed the lack of GRE on the platform, etc.  If you have dark fiber and the optics to drive it, put a dedicated GigE link on a pair and use that for the various VLANs that have to have L2 adjacency (vmkernel, plus all VLANs that contain VMs that migrate).