"DHCPACK on" vs "DHCPACK to"

David W. Hankins David_Hankins at isc.org
Wed Dec 31 18:14:39 UTC 2008

These questions were probably more appropriate for dhcp-users@, just
so you know.  Kind of on the line either way, but I err towards users.

On Tue, Dec 30, 2008 at 11:25:05AM -0600, Judson Bishop wrote:
> I am writing a SyslogScan::Daemon plugin for NAT rule updates and have a
> question concerning DCHPACK in the log file.

I'm sorry; our log messages aren't very machine readable.

Have you considered using execute() statements on 'on commit' events
instead?  I think the folks who wrote that patch did it for similar
purposes (firewall rules, etc).

> Is it correct that "DHCPACK to" is for a new lease and "DCHPACK on" is for a
> renewal?  

No; 'DHCPACK to' is only logged in reply to a DHCPINFORM.  The 'to' is
intended to be literally the destination address, whereas on other DHCP
messages, it's quite possible a DHCPACK on a given leased address will
be directed to other destinations (the limited broadcast address, or a
relay agent).

Note that DHCPINFORM replies, even though they are DHCPACK's, do not
grant or extend a lease.

> Also, I am testing on isc-dhcpd-V3.0.5 and looked through the code for 4.1.0
> and only saw "DHCPACK to."  Has the logging verbiage changed in the 4.X
> releases?

No, the 'on ...' log message is conditionally either a DHCPACK or a
DHCPNAK, so it's not surprising a simple grep doesn't find it.  If you
want to see where the 'on' message is logged, grep for;

	'Say what we're doing\.\.\.'

Which is a comment directly above the log line.

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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