Option 242 is used to give the phone the required parameters that it should use to connect to the PBX. There are two scenarios in which you can use option 242.

 

I am going to use the following VLAN IDs in my examples:

  • VLAN 100 – PC/Server Network
  • VLAN 200 – Voice over IP Netowrk

 

Scenario 1: Separate VLAN for Voice and Data

This is the most common configuration for VoIP networks. This works by having the option 242 set in both VLANs however it will be different in both.

First we need to set option 242 for VLAN 100

L2Q=1,L2QVLAN=200,VLANTEST=0

At this point our phone has gotten a DHCP lease that is telling it:

L2Q=1 meaning ON

L2QVLAN=200 meaning set the VLAN ID to 200

VLANTEST=0 meaning the timeout period for DHCP on that VLAN. 0=Infinite

 

Next we need to set option 242 for VLAN 200

MCIPADD=192.168.42.1,MCPORT=1719,HTTPSRVR=192.168.42.1,VLANTEST=0

Our phone has now switched it’s VLAN based on option 242 in VLAN 100. Now the phone, when requesting DHCP in VLAN 200 will get the option above. This will tell it:

MCIPADD=192.168.42.1 – this is the IP address of the PBX

MCPORT=1719 – Port the phone will listen on for signalling traffic to the call controller

HTTPSRVR=192.168.42.1 – Where to download firmware via HTTP. Typically same as PBX

VLANTEST=0 meaning the timeout period for DHCP on that VLAN. 0=Infinite

 

Now your phone should be booting in the correct VLAN and have the correct parameters pushed to it via DHCP.

 

Scenario 2: Shared VLAN for Voice and Data

The DHCP required for this scenario is much simpler. Simply add DHCP option 242 to your scope with the following string:

MCIPADD=192.168.42.1,MCPORT=1719,HTTPSRVR=192.168.42.1

MCIPADD=192.168.42.1 – this is the IP address of the PBX

MCPORT=1719 – Port the phone will listen on for signalling traffic to the call controller

HTTPSRVR=192.168.42.1 – Where to download firmware via HTTP. Typically same as PBX

 

Closing Notes

Please feel free to comment if you feel anything be added or better explained.