Cisco catyalist 3500series and vlans! HELP!!!

[toddgjinla1]

I'm really new to Cisco and vlans so this is really way over my head at the moment, but was wondering if someone could point me in the right direction on this. Basically i'm trying to put in some NEC IP phones that will go in 2 different locations that are tied togethere via 2 cataylist 3500 series switches. I've setup 2 vlans(one for data and one for voice) and configured ports on each switch to handle the voice vlan for the ip phone. Also, I've setup a trunck port between the switches to communicate the vlans. The IP phones work this way when I plug them straight into the switch on the configured vlan port and can communicate back to the phone system. I was wondering how I can setup ports on these switches to use a PC and IP phone on the same port. Basically have the pc plug into the switch on the back of the phone and then the phone into the switch. But I'm not sure how to do this since I've trying setting up the multi-vlan command on a port, but I can't use a trunk port at the same time to communicate to my other switch. Also, what if I want to add another cisco 3500 switch and more IP phones? Well I do know that the NEC phones automatically tag all voice packets. How do I pull this off? Do I need a router somewhere? Any advice would be great!!!

 

[ADB100]

I am not too sure how you would configure the NEC IP Phones for VLAN's but the I can explain the logic and then you can maybe apply this to your IP Phones & Switches.

Cisco implement Voice or Auxiliary VLANs - these are the same thing but the naming convention is different depending on the switch model. A Voice VLAN is a single 802.1q Tagged VLAN on an access port. Therefore with the following configuration:

interface FastEthernet0/1
switchport mode access
switchport access vlan 10
switchport voice vlan 20

There will be 2 VLANs on the port; an un-tagged VLAN which will be treated as VLAN 10 by the switch and a single Tagged VLAN with a Tag of 20. If you have the older 3500XL series switches you must make the port a trunk, instead of an access port as follows:

interface FastEthernet0/1
switchport mode trunk
switchport trunk encapsulation dot1q
switchport allowed vlan 1,10,20
switchport native vlan 10
switchport voice vlan 20

You must have some mechanism to inform the IP Phone to use 802.1q encapsulation and use the VLAN tag of 20. With Cisco IP Phones this is easy as it is done through CDP and there is no additional configuration necessary. If you have non-Cisco IP phones then this can be done in a number of ways:

1. Manual configuration on phone
2. Through Vendor Specific DHCP options in the Access/Native VLAN scope
3. Proprietary method where the IP PABX informs the IP Phone what VLAN it should use through a boot file (TFTP or BOOTP etc)

Manual configuration can be a pain as each phone will need to be 'touched' prior to installation. I have personally set up the DHCP options for Mitel & Ericsson IP Phones and both of them differ in what has to be configured but the logic is the same. Basically the IP Phone boots and broadcasts a DHCP request using un-tagged packets, when a DHCP Server responds it sends additional Vendor Specific information. One of the options the phone receives will be the VLAN number to use. Depending on the phone it will either accept the IP address, immediately release it and then start over using the VLAN tag. Either that or it will NACK the intial response and then start over using the VLAN tag.

I am not too sure whether they still do it this way but Ericsson used the 3rd way I describe, although this still relies on DHCP. Based on the DNS suffix received via DHCP the Ericsson IP Phone sends a HTTP request to a pre-determinned Server address, it then requests a configuration file (again the name is based on the DNS suffix) and this file should contain the configuration specifics for the phone, including VLAN tag.

You should consult the NEC documentation as to how they implement this behavoiur.

Good luck

Andy