Meaning of logmessages

Friesen, Don LCTZ:EX Don.Friesen at
Wed Sep 28 16:35:27 UTC 2011

>    The RFC states:
>	> The server SHOULD check the network address in a DHCPINFORM
>	> message for consistency, but MUST NOT check for an existing
>	> lease. 
>   That seems to be taken to mean that no configuration information should
>be taken from an existing lease even if one exists. I suppose it does not
>forbid using static configuration taken from any host entry (or parent 
>group) the IP address or ethernet address may map to but that could easily
>map to multiple, conflicting sets of parameters. What do you do if the
>DHCPINFORM request from a chaddr specifies an IP address different from
>the one the server would give it?

   Other bits from the RFC:

   >     The server forms a DHCPACK message containing the configuration
   >     parameters for the requesting client and sends the DHCPACK message
   >     directly to the client.
   > 4.3.5 DHCPINFORM message
   >   The server responds to a DHCPINFORM message by sending a DHCPACK
   >   message directly to the address given in the 'ciaddr' field of the
   >   DHCPINFORM message.  The server MUST NOT send a lease expiration time
   >   to the client and SHOULD NOT fill in 'yiaddr'.  The server includes
   >   other parameters in the DHCPACK message as defined in section 4.3.1.

Section 4.3.1 outlines the response to a DHCPDISCOVER, but includes the MUST, MUST NOT, MAY, and SHOULD behaviour for a DHCPACK.

My point is that regardless of the existence of a lease, the server should at least be consistent with the contents of the DHCPACK messages it sends to its own clients.  If a client has obtained parameters from the server via a DHCPACK that is in response to a DHCPREQUEST, then the DHCPACK that is sent in response to a DHCPINFORM should be consistent.

Don Friesen
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