I was playing with a six-year-old Cisco Catalyst 4006 switch today at work. The reason was that we have a small test network with servers and workstations which we use to, oddly enough, test things out. It used to all be on one big class-A subnet, but that doesn’t really resemble our real network in any way at all, which is an assortment of routed subnets and VLANs.
I’d used an array of different bits of kit to create a mini version of the real network – an old Cisco netbuilder router and some superstack switches (horribly slow), an old PC running FreeBSD and some mini switches, and most recently, a 48-port Cisco 3550 layer-3 switch. The 3550 was a loan from our comms team though, so it had to go back. I was instead given the 4006, which had for many years been used as a router for a handful of other subnets. It was now kicking about surplus to requirements as it had since been replaced with something newer.
I was told it ran both CatOS and IOS. ‘Not a problem’ I thought. It had a layer-3 routing blade (4232), so it was capable of routing. The routing blade ran IOS, so I just thought it’d be a case of configuring that and leaving CatOS alone.
Wrong!
As it turns out, as it is a ‘big’ chassis switch, CatOS takes care of all the switch ports, and VLANs, whilst IOS looks after the routing. I fiddled about with it for ages and couldn’t figure out what to do with it, until I found this incredibly handy guide.
My experience with CatOS was basically zero. All I knew, was it was different! With the 3550 switch, I had basically done the following things:
- Add VLANs
- Set IPs for VLANs
- Enable router rip
- Associate VLANs with ports
And that’s about it! With CatOS and IOS, it’s a little more complicated:
- CatOS commands:
- Add VLANs
- Set trunking
- Associate VLANs with ports
- IOS Commands:
- Create Port Channel interface
- Set IPs for Port Channel interfaces
- Enable router rip
Quite a bit more to do there! The more the dug into it, the more it made sense. Firstly, the backplane is treated like virtual gigabit ports. I assumed the backplane was ‘magic’. Plug in a blade, and suddenly your switch/router sprouted some extra ports. Whilst that’s true of the port-only blades, it’s not true of the layer-3 routing blade. So basically you have two logical devices (a router and switch) inside one big physical one. That confused me for a while!
It took me a while to work out why the layer-3 blade, which had two Gbics, and 36 switch ports, showed four gigabit ports when I did ‘show interfaces’. The reason is that ports three and four are ‘virtual’. They are the ‘ports’ plugged into the blackplane. Once I twigged that, it made perfect sense!
So now it was all configured, as per the instructions, it still didn’t work. After more fiddling, I remembered that IOS has an annoying quirk (I think anyway) whereby if there’s nothing plugged into any of the VLAN ports, it shuts down the VLAN. So as I only had something plugged into one of the ports, my pings would return with ‘destination host unreachable’. Once I plugged something pingable (a printer) into one of the other VLAN ports, it all sprang to life. I was super pleased!
My final crowning glory for it was to set the ip helper for one of the VLANs so that DHCP and PXE would work, and it was all working perfectly. It performs nicely now, so I’m pleased. For the record, the Cisco guide is a little confused. It says about plugging the routing blade into slot 2, which is how my 4006 was configured. All the examples and other info, refers to the blade as being in slot 3! The end result being that where it says something like “set trunk 3/1 nonegotiate dot1q 1-1005″ it should say “set trunk 2/1 nonegotiate dot1q 1-1005″. Not a major thing, and you’d hope whoever is following the instructions would spot it, but it threw me for a moment!.
