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New Member

HSRP & VRRP over DWDM Circuits

I have a business request to separate some of our systems across two geographically disperse sites. Some of the systems that need splitting use HSRP & VRRP as part of an automatic failover mechanism.

My question is, if we separated our pair of 6500's and pair of 4500's core switches and used WDM technology from a Service Provider to connect the switches together so that we can preserve the VLAN's across the two sites, what is the maximum distance that can be supported. (e.g. I know that the ZX GBIC's have a limit of 70km, presumably down a dark fibre).

I am aware that part of this limit is down to the optical path budget but I am also concerned if there are timeout limits (e.g. as a result of propogation delay etc) that will come into play and break the protocols.

Does anyone know what this maximum limit is as my search on the WWW & CCO has not revealed an obvious answer.

Many thanks in advance.

  • Optical Networking

Re: HSRP & VRRP over DWDM Circuits

Propogation delay is unlikely to be a concern for protocols such as HSRP and VRRP, which usually use hello intervals of at least a second during which light can travel around 200,000km through fiber.

What you may want to think about instead is whether or not running HSRP/VRRP over a WAN is the best way to accomplish your failover goals. I mention this because it's a pretty rare practice (usually routing protocols are used), though it may indeed make the most sense in your case.

New Member

Re: HSRP & VRRP over DWDM Circuits

It should work. However I would avoid extending Layer-2 across WAN links. Configure those Gig links across WDM as Layer-3 and rely on Routing Protocols for convergence.

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