Re: DHCP Leasing

Wonder the following situation, you've centralized your IP distribution
in a
main site and several sites, let's say 15 sites, all depend on the main
one
to get an IP.

All clients in the 15 sites have gotten an IP early in the morning and
then
at midday the link goes down for all 15 sites to the main site and, as
you
are lucky enough, there's a power down in those 15 sites.
By what you explained, all the clients would get an APIPA then...??

"Ben Smith" wrote:

> In article <1FC4E5F9-6F61-48AD-BC80->,
> says...
> > Client01 one leases an IP and so does Client02.
> > One hour after their leasing, the DHCP server goes down.
> > Client01 and Client02 have to reboot for any reason.
> >
> > After rebooting, Client01 maintains its IP address, as per the
leasing
> > expiration. Client02 releases the IP (remember they both have the
same
> > leasing period) for some reason.
> >
> > Both clients are Windows XP, and their behavior is expected to be
the same,
> > since they have the same TCP/IP configuration. They are in the same
subnet
> > and both can find the default gateway. No alternate IP is assigned.
> >
> > Any clue about why Client02 would release its IP before the leasing
time
> > expires?
> > Remember Client01 has the same config and does not release the IP.
>
> This is not quite how DHCP leases work. DHCP leases are controlled by
> the DHCP server, not the client.
>
> When a DHCP client reboots, after the IP stack is started, it issues a

> DCHP Discovery packet, if the DHCP servers that receive the broadcast
> respond with a Acknowledge packet. If the DHCP server that
acknowledges
> the client was the one that issued the address the client has cached,
> the client will request it in the Request packet, if the lease is
still
> active, the DHCP server will respond with a Offer package for the
> address and the lease time is reset.
>
> If the DHCP server is not online when the client reboots, the client
> will use an APIPA address and continue to rebroadcast a Discovery
packet
> every 5 minutes (2000 and later).
>
> As for why the two XP clients are behaving differntly, my guess is
that
> the network IP properties on each client are configured differently.
> Most likely, APIPA is turned off on Client01. Client02 is working as
> expected.
>
> If you would like to learn more about this I suggest reading the RFC
on
> DHCP (while boring as heck, if there is no better source for learning
> DHCP, which is a pretty simple protocol) and/or installing a network
> monitor and watching DHCP traffic.
>

Pedro Simoes