Redundant Redundancy

Date January 30, 2009

Many thanks to Ian Carder for this blog entry!

Over the past year we have replaced all of our remaining Cabletron network equipment with Cisco gear. Being a K-12 School District, we have to be extremely frugal where we spend out money. Often, this comes in direct conflict with going the extra mile to make sure whatever system we're deploying has some redundancy in the event of a failure.

Sometimes I can “sneak” redundancy in without having to pay a hefty price or fight for it. This involves simple things like RAID 1/5/10 on servers, dual power supplies, and dual supervisors in the Cisco core switches. We have been making heavy use of ether channel from MDFs to remote closets. That's a cheap solution assuming you have the available ports and don't feel like you have to over pay for Cisco branded GBICs. The other project we're looking to wrap up is creating more that one route to each building in the district using at least a hub network topology. Sorry, no spokes yet! The benefit here is that if we lose a single building, not all traffic is cut off between buildings on either side of the problem building. Lucky for us, we're all on one LAN, so no shared bandwidth to deal with. Just as with the ether channel situation, as long as you have the cabling between sites and available switch ports, it's a cheap proposition. I also have a small cluster running Novell's Cluster Services, but that was something I had to fight for. Beyond that, everything we have is single tier.

So I pose a couple of questions to the faithful readers; what critical services do you need to make redundant and what on the cheap tricks have you come up with to provide the redundancy?

3 Responses to “Redundant Redundancy”

  1. cmdln said:

    Still working on cloning myself. If anyone else is successful please let me know.
    It seems no matter what I do for redundancy or documentation it makes everyone feel better when I am around.

  2. Ryan said:

    I think the best move I made for network redundancy on the cheap was to move to Dell 6200 series switches instead of Cisco. Not that the 6200's have some redundancy feature that the Cisco's don't (far from it) but at $2500 for 48 ports (in a switch that stacks and has 10gig-e uplinks and redundant power supplies) it was so much cheaper that I was able to actually go with redundant access-level switches for servers, stacked to manage as one unit, with each ethernet port going to a different switch in the stack and those ports then bonded together (which you can do across stack members). RSTP then gets me redundant uplinks as well. These switches do support single-mode fiber GBICs, so you won't need a separate switch for inter-building traffic.

    That system not only saved me enough to afford redundancy at the (datacenter) edge, but gave me enough uplink bandwidth and low enough latencies that rather than using the layer-3 functionality of those switches in a ring topology and messing with routing protocols, I just have a single pair of core routers in each building, so I get backplane-speed routing between my VLANs, with VRRP on each subnet for failover between the core routers.

    Finally, since these switches do support layer-3 and ACL's (though the ACLs are a bit of a pain to configure) a stack of them is an easy core (/only) switching for a branch office.

    So not really a trick per se, just an opportunity to spend little enough on the original that you can afford a second set, and still get good quality.

  3. Ian said:

    You definitely pay a premium for Cisco switches. You can cheap out a bit if you stay away from their GBICs and go with something 3rd party.

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