IT Tip Of the Month - Change Your Managed Switch's Default IP

April 19, 2011

But which switch are you actually connecting to?

I assumed it was the one on the other end of the Ethernet cable. Checking the VLAN configuration revealed there were none so I assumed this switch was only part of the network I was deleting (I was combining two networks) and then just connected this switch to the other network.

And then nothing worked. And I spent the next 3 hours fixing things and got home around 2 AM…

I know now I had created an Ethernet loop. The switch I was configuring wasn’t actually the switch I was physically connected to, but some random one of the three identical 1800’s we have in our office (the 1800 actually supports STP, which I’ve never used, until now). After disconnecting all other cables from the switch I saw that this one did indeed have 3 VLAN’s and that the one I connected to the “other network” was actually the same one.

OK, so no default IP’s for managed switches. Ever. But which one do you give them then? My experience with switch IP’s is that no-one ever remembers them since they’re usually used very rarely (along with their admin passwords, but that’s a different “IT tip of the month”). Well, you use the 2 databases that occur naturally in any network - DNS and/or your firewall’s configuration (DHCP static map). In this case, I chose the latter.