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

[Eric Gauthier]

Hello,

I am not sure that you can bridge two subnets together using GRE, so
you may need some additional technology if your goal is to make the 
same subnet/IP float dynamically between locations.

With that said, if you use GRE, you'll want to make sure that the 
underlying transport between your data centers supports an MTU large 
enough to handle the GRE header without fragmentation.  

Eric 


On Wed, Jul 06, 2011 at 12:08:53PM -0400, 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?
> 
> Current network is L3 at the access layer w/ OSPF (4507-sup6 access, 4900M
> cores):
> 
>      A1
>      /\
>    /    \
>  C1------C2
>    \    /
>      \/
>      A2
> 
> Maybe it is better to just overlay stp back on to the network w/root and
> alt-root at C1/C2 (V1 and V2 are the proposed 3750X stacks)? Scary to me,
> but an an argument can be made for less complexity -vs.- tunnling/vpn
> based approach.
> 
>      A1     .V1
>      /\ . ' /
>    /. ' \ /
>  C1------C2
>    \` . / \
>      \/ ' . \
>      A2     'V2
> 
> OTOH, by the time this actually gets done maybe TRILL will be out ;)
> Hopefully this enterprisy topic is not too OT!
> 
> ~JasonG
> 
> 
> 
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/