what is the use of -a option of ISC relay agent

[Glenn Satchell]

>Date: Tue, 6 Jun 2006 04:57:46 -0700 (PDT)
>From: ashok singh <ashokr2k3 at yahoo.com>
>Subject: what is the use of -a option of ISC relay agent
>To: dhcp-users at isc.org
>
>Hi All,
>  
>  The ISC relay agent when started with -a option will append the  interface 
name through which the DHCP request came and forward it to  the DHCP Server. At 
the DHCP Server based on this interface name we can  do address allocations.
>  
>  This address allocation is anyways done implicitly based on giaddr field of 
incoming packet by DHCP Server.
>  
>  So my question is how this -a option can be useful?
>  
>  Regards,
>  Ashok

In the dhcrelay man page it says:

     The agent option field will contain two agent  options:  the
     Circuit   ID   suboption   and   the  Remote  ID  suboption.

These can be accessed on the dhcpd.conf using

  'option agent.circuit-id' and 'option agent.remote-id'

You might do this because you want to log this information, use
it to construct a hostname or perhaps in a billed or spawned
class or something similar. Like you said you don't need to use
it to determine the subnet.

You might also be using a different dhcp server that requires
this information.

regards,
-glenn