[c-nsp] DCI interconnects at L2 vs Encapsulated spanned Vlan

Arie Vayner ariev at vayner.net
Sat Apr 23 16:30:02 EDT 2016

Check brkdct-3060 from cisco live... It should give you some direction.


On Thu, Apr 21, 2016, 01:27 Peter Rathlev <peter at rathlev.dk> wrote:

> On Tue, 2016-04-19 at 08:12 +0000, Nick Cutting wrote:
> > If you use a L2 tunneling protocol over a L3 DCI - does this mitigate
> > all the L2 risks of a data centre interconnect?
> Not as such. The tunnelled packets have a TTL header and loops in the
> core are thus less of a problem, but L2 loops through the tunnel can
> still persist.
> If you have for example a set of VSS switches in both ends you can
> avoid loops altogether, but that goes for both mechanisms. And not
> everyone is equally happy about VSS/stacking/IRF and their ilk.
> > i.e. Would using encapsulation of the L2 frames be much better than
> > for example, running 3 Vlans over the link, using one for routing and
> > 2 for spanned vlans?
> I would personally prefer using the 3 VLANs over a trunk. A tunnelling
> mechanism introduces complexity that may outweigh the benefits.
> One benefit is the ability to re-route on link down fast enough that
> things like STP will not notice. You will see higher latency as long as
> the traffic is re-routed but no topology changes in STP.
> We use connections of both types, L2 with VLANs and L3 tunnelled via
> EoMPLS. We use the L3 tunnelled connections where the distance between
> the DCs makes it difficult and/or expensive to have a direct L2
> connection. We haven't really seen any problems with these tunnels.
> Their ability to survive connectivity problems via re-route has been
> very nice for us.
> --
> Peter
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