Cisco IOS updates – lessons learned

6 10 2009

One of the things I’ve learned the hard way about Cisco updates is that several things can (and usually do) go wrong if you don’t pay attention to what is going on.
1. Using the wrong IOS to update – if you pick one that lacks features (or one that disables features) you need, your router or switch will “die”. There is no easy way to learn this, you just have to figure it out. Pick carefully grasshopper.
2. Not having enough space – IOS will usually tell you before you start copying that you are out of luck, but that usually leads to the next problem…
3. Deleting files you really need – I thought I was smart – my router didn’t have enough room to fit everything so instead of worrying about it, I just formatted flash and I was ready to copy. The problem is that format destroys vlan.dat – a file you probably need. Don’t delete or format if you don’t know what you are doing. Or even better, if the device has a place for a compact flash card, get a bigger one and use it and have multiple IOS images!
4. Crapping out on a TFTP transfer – One thing about having a far flung network is that you quickly learn how slow and unreliable your connections are — !!!00!!!000!!!! If you don’t know what that is, then this comment may be wasted on you. Think about what you are doing and try to put the files as close to the updated device as possible. USB stick plugged into the device is best, or a machine on the local LAN if USB doesn’t work or isn’t an option. You will thank me later. !!0!!0!!0000!0!