DHCP option 242 string handling for Avaya IP phones

Unanswered Question
Mar 18th, 2008
User Badges:

Is it possible to handle via a local IP DHCP configuration on a 3560 switch any DHCP option e.g. #242 with the necessary information(s) in a string (like 'MCIPADD=192.168...etc.')?

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Peter Marshall Fri, 10/23/2015 - 12:40
User Badges:

Dynamic Host Configuration Protocol (DHCP) can be configured either on a server or on the router. In many cases, the main site DHCP server may already have the correct scope and configuration for option 176 or 242 as needed. Since remote sites may not warrant the added expense of a server, the DHCP option commands can be configured on that remote site's router. DHCP options are vendor-specific. There is no single document I've found that addresses all the issues I'm going to cover here, so comments are more than welcome. I noticed this is an 8-year old thread.

Keep in mind that VLAN separation is a fundamental best practice on the LAN that also defines the relationship between the switch and local router. Do not enable IP routing on your switches even if they have that capability. Keep in mind that minimizing data loss, jitter and delay are critical for voice applications. Avoid technologies that are historically unfriendly to voice, such as VPN, or GLBP.

The network and phone systems should be properly configured with time synchronization, such as Cisco's Network Time Protocol (NTP). Also, make sure you're on the same page with the phone engineers regarding timezones. Here's an example if you're in the US Midwest:

clock timezone CST -6
clock summer-time CDT recurring

Avaya 4600 Series phones use Option 176 as the default DHCP Site Specific Option Number (SSON) with TFTP or HTTP. The 1600 and 9600 Series phones use Option 242 with HTTP or TLS. Both IP telephones use these servers as file servers, to download firmware and access scripts or settings files.

Avaya uses a 46xxsettings.txt file that contains everything. The generic 46xxsettings.txt file is available for download from Avaya. That file resides on an Avaya server and your routers need to point to that server. Avaya engineers know how to tweak this file if necessary.

Router configuration example (first, reserve the IPs you don't want assigned via DHCP):

 ip dhcp excluded-address
 ip dhcp excluded-address

DHCP configuration with DHCP option 242:
ip dhcp pool VoIP
 domain-name yourcompany.com
 option 242 ascii MCIPADD=[up to eight Avaya Call server IPs],MCPORT=1719,HTTPSRVR=[IP of Avaya HTTP server],HTTPDIR=[directory where the 46xxsettings.txt file resides]

If you have a supplicant set up (wall jack -> IP phone -> PC), include the L2QVLAN because the phone will boot in the data VLAN; tell the IP phone to hop over to the VoIP VLAN:
option 242 ascii MCIPADD=[up to eight Avaya Call server IPs],MCPORT=1719,HTTPSRVR=[IP of Avaya HTTP server],HTTPDIR=[directory where the 46xxsettings.txt file resides],L2QVLAN=70

If you also have older Avaya phones, include the DHCP option 176:
option 176 ascii MCIPADD=[up to eight Avaya Call server IPs],MCPORT=1719,TFTPSRVR=[IP of Avaya TFTP server],TFTPDIR=[directory where the 46xxsettings.txt file resides],L2QVLAN=70

So, why up to eight Avaya Call servers in the MCIPADD option? Generally, you have a main site, so the first IP address will be the same for all your remote sites. That first address is your main, central, call server. If you have backup Avaya servers at a remote site, list the remaining IP address(es) - separated by a comma.

Note: if you do not manually configure the L2QVLAN setting, it may revert to your default VLAN. That may be undesirable.

Subinterface (to keep things simple, use the same number in your IP, subinterface, and VLAN):
interface GigabitEthernet0/2.70
 encapsulation dot1Q 70
 ip address
 no shutdown

Switch configuration:
disable cdp globally (cdp is not friendly to many non-Cisco IP phones)
enable lldp for switchports connected to Avaya devices for 802.1x
enable qos

Configure separate VLANs for voice and data separation:
Vlan 3
name DATA

interface Vlan3
description DATA
 ip address
 no shutdown

Vlan 70
 name VOICE

interface Vlan70
 description VOICE
 ip address

Switchport configuration (VoIP VLAN only):
standalone IP phone:
interface GigabitEthernet0/1
 switchport mode access
 switchport access vlan 70
 switchport nonegotiate
 mls qos trust dscp
 priority-queue out

Trunk or uplink
interface GigabitEthernet0/52
 description [uplink - router or another switch]
 switchport trunk allowed vlan 3,70
 switchport mode trunk
 switchport nonegotiate
 mls qos trust dscp
 priority-queue out

IP phone supplicant configuration (VoIP & data vlans):
interface GigabitEthernet0/1
 switchport mode access
 switchport access vlan 3
 switchport voice vlan 70
 mls qos trust dscp
 priority-queue out

Helpful Avaya documents (yes, they're old, but provide thorough explanations):



This Discussion