VLAN Configuration Basics

Unanswered Question
Jan 12th, 2008

I recently read in a CCNA book that you can only configure VLAN's one port at a time. There is no command available with older switches, like a 1900 series, that lets you assign more than one port to a VLAN at a time. I am a little confused by this. In our situation, we need to set up VOIP. The technical specs at this point seem to suggest that the only way we can do this is to purchase a 3548 XLFETH Cisco and assign VLAN's to the switch. One VLAN will be the VOIP and the other will be for the pc (data).

What would the basic commands be to allow each port to have two VLAN's on it? And how would I allocate bandwidth? The VOIP provider said that it "only" consumes about 30 Mbs, but I don't know if that is correct.

I have this problem too.
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Edison Ortiz Sat, 01/12/2008 - 19:01

1) A port can carry more than one Vlan by changing the mode from access to trunk. Trunking is supported in all catalyst switches. You can also have a voice Vlan and a data Vlan on the same port.

2) 3548 ? You can't purchase that any longer. Current models are 3560 and 3750 (if you want Layer3) and 2960 (if you want Layer2).

3) Bandwidth allocation depends upon the switch you decide to purchase. Be sure to read the documentation on the switch and concentrate on QoS.

jlcarey1usa Sun, 01/13/2008 - 06:57

We will be purchasing used/refurbished equipment because there is no way the management will approve two new switches that could run 8-10K. You said, "You can also have a voice Vlan and a data Vlan on the same port." Well, that is exactly what we will need to do. So, by choosing trunking, I will be able to achieve that?

Edison Ortiz Sun, 01/13/2008 - 07:48

Trunk will carry multiple Vlans but you need devices capable of understanding 802.1q trunking at either end (most phones do).

You can also implement access and voice vlan on the same port. The phone will understand that it belongs to the voice vlan, not the data vlan.

Here is some information on Voice Vlan


In short, the VoIP device you are planning to use, it's the deciding factor on what kind of configuration must be done at the switch side.

Another word of advice, VoIP is an emerging technology. Purchasing outdated equipment is not recommended. If you encounter any bugs on the switch side, you will be in a tough situation as the equipment will be out of warranty. Something to consider and suggest to upper-management.





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