Is this because you have an IP telephone connected to the switch port and a computer connected to the second network port on the telephone, and you want these clients in separate VLANs?
Basically, you design your Voice and Data as two networks. eg, you have 10.1.10.0/24 for Data, 10.1.20.0/24 for voice Each network has its own subnet and has a router, or "defaut gateway", address. eg, you have 10.1.10.1 for Data, 10.1.20.1 for Voice. Then, you can put both networks on the same switch by using VLANs. Eg, VLAN10 for Data, VLAN20 for Voice. Next you need to choose where the routing in and out of that subnet is going to take place, so this is your router/default gateway address. This is a design decision - in a normal network you can do this on any one of, - a Layer3 switch - a router - a firewall Finally, you need to make the VLANs available to the network hosts like computers and phones. To know that something is in a particular VLAN, you use one of 2 rules: - assume everything that has no VLAN tag belongs to VLAN X - read the VLAN tag to find out what VLAN it is in.
The normal setup is to configure all your switchports with VLAN10 (Data) untagged and VLAN20 (Voice) tagged.
