doubt dhcp relay agent.circuit-id and remote.circuit-id

Ricardo Barbosa spiderslack at
Sat Mar 16 14:04:02 UTC 2019

Hi, I'm testing dhcrelay and tested successfully with the -a option, but this option generates a circuit-id, Is there an option that I can set the circuit-id and even the remote-id?
Reading the manpage of dhclient and dhcp-options I found:
The send statement
  send { [ option declaration ] [, ... option declaration ]}

The send statement causes the client to send the specified options to
the server with the specified values.  These are full option
declarations as described in dhcp-options(5).
Relay Agent Information Option

An IETF draft, draft-ietf-dhc-agent-options-11.txt, defines a series of 
encapsulated options that a relay agent can add to a DHCP packet when 
relaying it to the DHCP server. The server can then make address 
allocation decisions (or whatever other decisions it wants) based on 
these options. The server also returns these options in any replies it 
sends through the relay agent, so that the relay agent can use the 
information in these options for delivery or accounting purposes.

The current draft defines two options. To reference these options in the 
dhcp server, specify the option space name, "agent", followed by a 
period, followed by the option name. It is not normally useful to define 
values for these options in the server, although it is permissible. 
These options are not supported in the client.

option agent.circuit-id string;

The circuit-id suboption encodes an agent-local identifier of the 
circuit from which a DHCP client-to-server packet was received. It is 
intended for use by agents in relaying DHCP responses back to the proper 
circuit. The format of this option is currently defined to be 
vendor-dependent, and will probably remain that way, although the 
current draft allows for for the possibility of standardizing the format 
in the future.

option agent.remote-id string;

The remote-id suboption encodes information about the remote host end of 
a circuit. Examples of what it might contain include caller ID 
information, username information, remote ATM address, cable modem ID, 
and similar things. In principal, the meaning is not well-specified, and 
it should generally be assumed to be an opaque object that is 
administratively guaranteed to be unique to a particular remote end of a 

it mentions that these options are not supported on the client, only on 
the relay, but looking at dhcrelay does not have a configuration file, 
how would you use these options in a relay. That from what I understand 
and does not exist. If anyone can explain it. Thank you very much.

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