in Networking

getting VLANs working between Cisco & HP gear

Ever since I started at Devlin, I’ve had one nagging problem with the network gear: the VLANs from the Cisco equipment (a triad of Catalyst 3550-24 switches) won’t propagate to the other gear we have (an HP ProCurve 2424M and a Linksys SRW2024). I read all I could about VLANs and tagging, but no matter what I did I couldn’t get the non-default VLANs to show up on anything but the Cisco gear. I figured I was missing some key information, particularly about when to tag and not tag VLAN traffic, that was preventing me from getting this working.

I finally did a search on Google about Cisco interoperability, and found this page which indirectly made everything clear. It turns out that the tagging on the HP (or any other switch being connected to the topology) needs to be done as follows:

  • set traffic on the trunk port to be tagged for every VLAN you want to propagate
  • allow access to the VLAN on the non-trunk ports but set them to be untagged

I was originally a little worried because the VLAN I’m interested in propagating is the voice VLAN (for our IP telephony setup) and I feared that the Catalyst would do something really weird with it (seeing as how you specify switchport voice vlan 2), but it seems to be just another VLAN. I assume the foregoing IOS directive is just for QoS or something on the Catalyst.

By the way, doesn’t the University of Wales’ IT department have an awesome name? I know it’s Gaelic, but I should start calling my department Gwasanaethau Gwybodaeth too. That would certainly cut down on the help tickets — I could start saying “please e-mail [email protected] to open a ticket” 🙂

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  1. It's not gaelic… It's Welsh 🙂

    The literal translation is as follows

    Gwasanaethau = Services
    Gwybodaeth = Information

  2. The command "switchport voice vlan 2" is used when connecting IP phones to a switchport. The IP phones will set up a trunk between themselves and the switch – you set the vlan you want the PC connected to the back of the phone to be on with the "switchport access vlan" command and use the other "switchport voice" command to specify the VoIP vlan.