subenet-mask option in DHCPACK for DHCPINFORM

Jane Du (jadu) jadu at
Mon Jul 23 20:37:22 UTC 2007


Hi David,

If I understood correctly, you are saying that ISC DHCP server does send
option 1 in DHCPACK to DHCPINFORM.
I just checked the code dhcpinform() in dhcp.c for version 3.0.6. It
seems to be the case.

Actually, the dhcp client we are using doesn't like that the subnet-mask
option is included in the DHCPACK when it doesn't request it. The vendor
of the client told us that we need to change the code by not sending the
option because it doesn't follow the spec. In RFC 2131, the option 1 is
not a "must" added option in the ACK, right? 

Do you see any issue if I just change code not to send option 1 when it
is not requested?

In which version, does ISC server start sending the subnet-mask for the
ack to request?  I don't see such behavior in 3.0.4.



-----Original Message-----
From: dhcp-users-bounce at [mailto:dhcp-users-bounce at] On
Behalf Of David W. Hankins
Sent: Monday, July 23, 2007 11:17 AM
To: dhcp-users at
Subject: Re: subenet-mask option in DHCPACK for DHCPINFORM

On Mon, Jul 23, 2007 at 11:01:03AM -0700, Jane Du (jadu) wrote:
> Is it implementation intent that DHCPACK in responding to DHCPINFORM 
> always has subnet-mask option along with the options requested by the 
> client? It seems to be the case even when the client doesn't request 
> this option.

No, this is an oversight.  We started sending the subnet-mask in
discover/offer/request/ack to match other server implementations (and to
be compatible with clients which are dependent on this behaviour).

That is also affects dhcpinform was an error.

Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
Why settle for the lesser evil?
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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