POC – Post #3

Another small post to my ongoing POC series.

I’ve changed the title, it doesn’t really make sense to post it “day x” any more because I rarely get to work a full day on it. I also seem to spend far more days doing other projects than I do on this one.

Anyway, as usual, a bit of a pic of how it’s all looking:



The Limits of Spanning Tree

You may notice there is a bit of copper cabling in this one (it has since been removed). This was part of my setup for upgrading all the IOSs on the CGS-2520s. I added a link between each CGS-2520 and the next one down the rack, gave each one an IP address on VLAN1 and then did a archive download-sw tftp. This seemed like the quickest way to upgrade about 64 boxes as the ports on the CGS are by default in VLAN1.

As I did this, I came across an interesting issue. Spanning tree by default on Cisco devices has a “diameter” of 7. This diameter is used to calculate the various spanning tree timers. It’s not actually the number of switches you can have in a row before it breaks. Nope, that’s 22.

I’m not even kidding. I had all the switches in one long daisy chain and when I got to switch 22 VLAN1 would continue to bounce up and down. Easy fix – I just added a link between switch #22 and the root. But it was interesting, I have never actually seen the limit before – luckily I have never had to work in an environment with 22 switches linked together in a row! So yeah, don’t do that.

Random CGS 2520 Facts

#1 Default power draw: about 500mA at 53V, or about 26W.

If you plug a CGS in with no real traffic, have a couple of SFPs inserted, no POE ports – it will draw about 26W. Which brings us too…

#2 Number of CGS 2520s you can run off a 1A C curve breaker: 2.

Just. You have to double tap em. Once on to fill the caps then again to turn it on properly. Probably not the best idea in the world. But it works if you need it to. We had mostly 1A breakers on hand.

#3 The 100MB SFP ports are by default half duplex. Er…I know 100MB ports by default negotiate to half duplex…but come on. They are fibre ports….? Just…annoying.

Random Annoyance with the CGR 2010

If you get an upgrade license for a CGR (or any other router). Get the product code right. This may seem obvious, and it is. But, damnit, it’s annoying if you don’t.

Do a show license udi and make sure you write it in exactly as the PID. We accidentally put in “CGR2010/K9” instead of “CGR-2010/K9”. And then the Cisco web page seemed to be crashing for the afternoon – so that was annoying.

Other than that, still waiting on the last couple of fibres (and by couple, I mean the last 72). All the devices have Loopback and point to point addresses. Will add basic OSPF soon (hopefully tomorrow) and then I can get going on the fun stuff.

/Tom out.

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3 thoughts on “POC – Post #3

  1. I have a bunch of these switches installed at substations and they randomly loose ethernet connections to the Swietzer Engineering Laboratory (SEL) devices. The port shows UP/UP but you can’t ping across it, this never happened when we had the old 2950’s out there, I’ve had a TAC case open for a year with no luck. Have you ever heard of anything like this?

  2. Can’t say I have seen anything like that yet. Do you have any idea at what layer it’s failing? Is the end device in the MAC table? Is there an ARP entry for it? Does it happen to all devices within the VLAN or just one at a time? What version of IOS are you running?

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