You’re migrating/building a new DHCP 2012 server and find that 242 option does not exist within scope options.

Here is how to add:

1) Launch DHCP
2) Expand DHCP and right click IPV4
3) Click ‘Set Predefined Options’
4) Click Add

5) Type in details

Name: 242 Avaya
Data Type: String
Code: 242
Description: Avaya Phones

6) Click ok

7) In the string value, type your AVAYA string, for  for example: MCIPADD=192.168.2.8,MCPORT=1719,HTTPSERVER=192.168.2.8

8) Click OK

9) Revisit your Scope Options, scroll to the bottom and add

If you are running a DHCP HA (Failover), the scope will need to be added to the partner server, the settings will not replicate.