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

[Michele Bergonzoni]

Il 06/07/2011 18.08, Jason Gurtz ha scritto:
> 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.

Remember that you cannot bridge over a GRE tunnel, and cannot terminate 
any kind of tunnel on a 3750 (pretty sure) or a 3750-x (less sure, but 
it's in the release notes). From what I understood of your pictures, 
you're planning to make a tunnel interface on V1 (unsupported on this 
platform), and put it in a bridge-group (unsupported anywhere AFAIK: the 
R in GRE stands for "Routing"). You could try with L2TPv3, but I think 
it is unsupported on the 3750[-x].

If I get the pictures right, you could get away with a VLAN on C1 with 
two ports in dot1q tunnel mode + l2protocol tunnel stp, and a similar 
situation in C2, so V1 and V2 will have their own spanning tree and C1 
and C2 will not partecipate in it (if you need also L3 in V1/V2, you 
will have to use a different physical interface).

But I'd rather use dark fiber if at all possible, as Gert said. Or 
elaborate on the fact that Layer 3 is by definition the layer where 
things like forwarding, routing around failures, etc. take place, and 
servers should learn to live with it: this is hard to swallow after 
years of VMware and Microsoft NLB, but that's the hard truth.

Regards,
				Bergonz


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Ing. Michele Bergonzoni - Laboratori Guglielmo Marconi S.p.a.
Phone:+39-051-4392826 Fax:+39-051-6153683 e-mail: bergonz at labs.it
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