Subject: Renew after a move to another subnet while powered up

From: "Dean Parkinson" <[email-masked]>
Date: Thu, 6 Apr 2000 12:47:27 -0400

I would like to know whether a DHCP Server should send a NAK if a client
moves from one subnet to another while still powered up and the renew is
sent from the client to the server at the proper time (1/2 the lease time).

Here is the scenario.

I have two subnets and each have a range that is served by the same DHCP
Server.  A laptop is plugged into one of the subnets and is started.  The
lease that is given out to the client is for 1 hour.  Five minutes later the
laptop is unplugged and plugged back in to a connection on the second
subnet.  The user did not shut the machine down.  They just unplugged the
network cable, moved to say an adjacent office, and plugged back in.
However, the new connection is on another subnet from the first.  When
another 25 minutes goes by the laptop does a renew.  At this point I would
like to know what the DHCP server should do.  Should it send a NAK, should
it stay silent or should it send an OFFER?  In your response could you
please indicate where in RFC 2131 it gives the proper behaviour?

Thanks,
Dean Parkinson

---

From: Ted Lemon <[email-masked]>
Date: Thu, 06 Apr 2000 12:00:28 -0700

> At this point I would

When the client is in the RENEWING state, it's unicasting its
DHCPREQUEST, so the server will never see it, because the client can
no longer contact its router.   If the server *did* for some reason
get the DHCPREQUEST message, it would not know from what subnet it
came, and therefore would not be able to determine whether or not it
should NAK the message.

At 85% of the lease duration, the client should go into the REBINDING
state, at which point it will broadcast its DHCPREQUEST message.
The server will get this message, see that the IP address is wrong for
the subnet, and send a DHCPNAK at that time (assuming it's configured
correctly).

			       _MelloN_