Client classing

Glenn Satchell Glenn.Satchell at
Tue Jun 26 13:27:59 UTC 2007

>From: Morten Andersen <morten at>
>To: "dhcp-users at" <dhcp-users at>
>> Failing any specific option you could always extract that piece of
>> information from the packet directly. The function packet() is
>> described in the dhcp-options man page.
>>     packet (offset, length)
>>       The packet operator returns the specified portion  of  the
>>       packet  being  considered,  or  null  in contexts where no
>>       packet  is  being  considered.    Offset  and  length  are
>>       applied  to the contents packet as in the substring opera-
>>       tor.
>Thank you for your response. This sounds like a solution that can work
> but I can`t find any information about the packet() function,

packet extracts a specified chunk from the packet currently being
processed. You'll need to use a packet capture to look at the contents
of the packet and work out the bytes you need.

The snippet above is from the dhcp-options man page.

> but I found "RELAY AGENT INFORMATION OPTION" in the dhcp-options man
> page and I think this can help me. One tiny problem now is that the
> man-page does not mention how to set the parameters on the dhcrelay
> agents. Anyone? :)

man dhcrelay
     If the -a flag is set the relay agent will append  an  agent
     option  field  to  each  request before forwarding it to the
     server.   Agent option fields in responses sent from servers
     to clients will be stripped before forwarding such responses
     back to the client.

     The agent option field will contain two agent  options:  the
     Circuit   ID   suboption   and   the  Remote  ID  suboption.
     Currently, the Circuit ID will be the printable name of  the
     interface  on  which  the  client request was received.  The
     client supports inclusion of a Remote ID suboption as  well,
     but this is not used by default.

Maybe time to go look at the source...


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