dhclient option 120

Peter Rathlev peter at rathlev.dk
Wed Sep 21 09:07:27 UTC 2011

On Wed, 2011-09-21 at 10:38 +0530, mayank tyagi wrote:
> i am new to dhclient stuff , i want to know who initiates request for
> DHCP option 120 and is there any specific message which is used for
> same purpose?

The dhclient program initiates the request. The server only serves
requests that the client has asked for. And only the dhclient program
talks to the DHCP server.

>   as you suggested that its the responsibility of application to
> extract, so will it be the application who initiates this request? in
> my case its SIP UE which want to obtain to obtain SIP server ip
> address.

You need some kind of interworking between dhclient and your
application. You have already manually configured dhclient to ask for
the option. You could the let dhclient write the option to some file the
application will look at, or you could let the application inspect the
current lease.

Regarding decoding the value of an option 120: If the application cannot
do this by itself, it doesn't seem that hard to do manually with e.g.


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