Installation guide

Additional Information

DHCP OPTION 120 SUPPORT

DHCP Option 120 (as referenced in RFC 3361) allows SIP clients to locate a local SIP server

(i.e. outbound proxy server) that can be used for all outbound SIP requests. Using the “use

dhcp option 120” configuration parameter, Administrators can now enable support for DHCP

Option 120 on the 6800i SIP phones. This is particularly useful when service providers require

the phones to use certain outbound proxy servers or Session Border Controllers (SBCs) based

on geographical location and have provisioned the outbound proxy by using DHCP Option 120.

The parameter is disabled by default.

Considerations

The following considerations must be taken into account when enabling support for DHCP

Option 120 on the IP phones:

• If the parameter is enabled and DHCP Option 120 contains a valid value, the phones will

use the server IP/name obtained via DHCP Option 120 as the outbound proxy for both the

Global SIP and Line 1 profiles.

• If Line 2 is configured and the outbound proxy is not defined, the phone will use the outbound

proxy located in the Global SIP profile.

• If Line 2 is configured with a valid outbound proxy, the phone will retain the configured Line

2 outbound proxy and ignore the Global SIP profile. This allows for Line 2 to be registered

to another service with another outbound proxy if required.

• If Line 2 is configured for another service but no outbound proxy is wanted/required, ad-

ministrators should not leave the outbound proxy as undefined (i.e. 0.0.0.0) as the phone

will use the outbound proxy located in the Global SIP profile. Instead, administrators should

specify the proxy/registrar’s address as the outbound proxy.

• If the parameter is enabled, but the server does not have an outbound proxy configured,

DHCP Option 120 is ignored and the phone will behave as if the parameter is disabled.

• As Option 120 does not support port numbers directly, if a non-standard port (i.e. other than

5060) is required, this must be set using the configuration parameter “sip outbound proxy

port” or by the use of DNS SRV in which case “sip outbound proxy port” must be set to 0.