Subject: [dhcwg] Client Identifier interpretation

From: "Kostur, Andre" <[email-masked]>
Date: Fri, 17 Jun 2005 10:18:53 -0700

In section 2 of RFC 2131 says:

   The 'client identifier' chosen by a
   DHCP client MUST be unique to that client within the subnet to which
   the client is attached. If the client uses a 'client identifier' in
   one message, it MUST use that same identifier in all subsequent
   messages, to ensure that all servers correctly identify the client.

Does this leave open the possibility that device may obtain a lease without
supplying a client ID, but in subsequent transactions start using the Client
ID?  From a strict reading of the above statement it says that once the
client sends the client ID, it must continue sending the client ID, but
doesn't explicitly exclude the possibility that the device may start without
a client ID, and then start using it.

Having said that, how would that interact with Section 3.1:

  6. The client may choose to relinquish its lease on a network address
     by sending a DHCPRELEASE message to the server.  The client
     identifies the lease to be released with its 'client identifier',
     or 'chaddr' and network address in the DHCPRELEASE message. If the
     client used a 'client identifier' when it obtained the lease, it
     MUST use the same 'client identifier' in the DHCPRELEASE message.

If the client started without a client ID, but then starts using one, which
should it use in the Release?  According to 3.1.6, it should use the client
ID that was used to obtain the lease (that is, _no_ client ID), but
according to section 2, the device MUST use the client ID in all subsequent
messages.

Or... is a third interpretation that if the client ID isn't supplied in the
discover, that the DHCP server should never try to use the client ID when
dealing with this client device?  (Which still leaves the question of which
to use in the Release)

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From: Ted Lemon <[email-masked]>
Date: Fri, 17 Jun 2005 11:31:16 -0700

If a client uses the client identifier in some cases and no client  
identifier in other cases, it is two different clients, and should  
get two different IP addresses.   Some DHCP servers make a special  
case that if the client identifier is what you would get from  
generating a client identifier from the hardware address, then the  
two are treated as the same identifier, but this is not what the  
standard says, and not all DHCP servers do this.   If you are writing  
a DHCP client, it should just be consistent about what identifier it  
uses.   If you are trying to adapt to a broken DHCP client, all bets  
are off - do what you have to, but don't call it standard!   :')