So, I’ve been rationalising a small remote site’s network infrastructure and thought I would use some existing spare kit to try to “improve” the network  architecture. So, there was a Cisco 2800 series router and some little switch with a couple of servers plugged into it. Not much but important enough. I figured I would deploy a second 2800 and add a HWIC-D-9ESW to both 2811s. Join them with Etherchannel and set-up GLBP between the routers before the traffic headed onwards.

So a couple of obvious caveats – The Cisco 2800 (and 1800 and 3800 series too) is nearing end of supported life. This is on a budget and new kit is not an option currently.  A shiny new pair of layer three switches would have worked too – simple dual network links with some dynamic routing. Many ways to skin this fish 🙂 Anyhoo. I came across a few limitations of my plan

1) The HWIC-D-9ESW has a hard limit 0f 15 VLANs (which needs to include the VLANs 1002/1003/1004/1005, so 11 usable VLANs). Not very many if you plan on joining the ESW modules to an existing VTP domain with a few segments.

2) The HWIC ESW modules can’t do Etherchannel. So bonding a pair of links between two ESWs or between an ESW and another switch is not possible

3) Cisco do not support GLBP on SVIs with ESWs. Hmm, HSRP and VRRP are supported however. (I did setup GLBP between an SVI on each device and GLBP appeared to work. I didn’t do thorough testing though, so there are likely to be some gotchas- even though it seems to work).

Some of these limits are described in “Switch Virtual Interface for Cisco Integrated Services Routers” (PDF), “Cisco HWIC-4ESW and HWIC-D-9ESW EtherSwitch Interface Cards“, “Cisco 2800 Integrated Services Routers“.

So, long story short, two routers using HSRP with a single link between them (could use two links and have STP block one) each connected to the upstream connection. At least now the remote office has some level of network resilience.

The point of this post – in case you missed it!! – was that some “simple” features one takes for granted on “normal” Cisco kit can be lacking or missing entirely one lower end devices. Once again, it pays to completely check the vendor support matrices and feature sets. In this instance, it was quite tricky to find a definitive list of available (or disabled) features.


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