How to pass DHCP requests for Nortel IP Phones behind NAC
The process for a Nortel IP phone to connect to the Nortel IP PBX requires two steps. First the phone makes a DHCP request on the native or DATA VLAN and the DHCP offer provides the VOIP VLAN tag. Then the phone then makes a request for a DHCP address on the VOIP VLAN and is also directed in that DHCP offer what the identity of the IP PBX is and how to communicate with it. To provide for this to work we need to add a DHCP option regarding the VOIP VLAN ID on the DATA DHCP scope and also add a different DHCP option to the VOIP DHCP scope to identify access to the IP PBX.
1. Click on the Windows Start button. Select Programs > Administrative Tools > DHCP. The administrative console window
opens.
2. Highlight DHCP and expand the DHCP option (if it is not already expanded).
3. Highlight the server and right-click to open the pop-up menu. Select Set Predefined Options from the menu. Do not go
into the Vendor Specific settings. The Predefined Options and Values window opens.
4. Click Add. The Change Option Type window opens.
5. Enter the desired Name. For this example, the name of "Nortel-i2004-A" is entered.
6. Select Code 128.
7. Click OK to close the window. The Predefined Options and Values window reopens with the string 128 Nortel-i2004-A
entered in the Option name field.
8. Under the Value area, enter the following string in the String field: "Nortel-i2004-A,x.x.x.x:4100,1,10." using the
following guidelines:
· The string is case-sensitive.
· Place a period at the end of the string.
· Commas are used as separators.
· Spaces are not allowed.
· x.x.x.x is the IP address of the IP Telephony node.
· If it is a BCM, replace the 4100 value with 7000.
9. Click OK.
10. Click Add. The Change Option Type window opens.
11. Enter the desired Name. For this example, the name of "VLAN-A" is entered.
12. Select Code 191.
13. Click OK to close the window. The Predefined Options and Values window reopens with the string 191 VLAN-A entered in
the Option name field.
14. Under the Value area, enter the following string in the String field: "VLAN-A:AAA+BBB+CCC." Using the following
guidelines:
· The string is case-sensitive.
· Place a period at the end of the string.
· "+" are used as separators.
· Spaces are not allowed.
· AAA, BBB, or CCC is the numeric value of the voice Vlans, there can be up to 10 Vlans identified.
15. The Code 128 must now be added to the applicable VOIP scopes and the Code 191 must now be added to applicable DATA
scopes.
Click on the scope (Scope [x.x.x.x] name) to expand the scope, then click Scope Options.
16. The Scope Options window opens.
On the General tab, scroll to the bottom of the list and check the 128 Nortel-i2004-A option
and the 191 VLAN-A option show up under their respective scopes.
17. Click OK. The Option Name and Value appear in the right pane of the administrative console window.
Configure a Windows 2000 server with DHCP services using the DHCP Manager. More information can be found here: [1]
