Two elementary questions on LANs

Tim ignored_mailbox at
Thu Jun 16 16:46:44 UTC 2011

On Thu, 2011-06-16 at 16:27 +0200, Timothy Murphy wrote:
> It's as though there is a lease somewhere 
> and I have to wait for it to expire.

That's when you use commands like "dhclient -r" to try and get your
client to release its current lease.

In the absence of being told to use some specific IP, a client will
generally ask to use the same IP as it used last time.  Removing DHCP
data on the client may stop this, causing the client to just as for an
IP, not a specific one.  And removing DHCP data on the server may cause
it to assign a different IP, so long as the server is randomly doling
out IPs.  But if it has a fixed set of rules, than the server will try
to give it the same IP.

I don't know about Linux clients, but other personal computers were
known to try requesting their prior IP, and if not assigned anything
else may actually just go ahead and use it.  Though, that's a very old
behaviour.  These days, it's more common for a client to assign itself a
random IP, in a completely different range, if it doesn't get given one
by a server.

It's a long time since I fiddled with DHCP servers, trying to
deliberately change addresses.  But I remember doing things like:

Getting the client to release its IP.
Stopping its network.
Stopping the DHCP server, changing its configuration, deleting data from
its lease file, then restarting the server.
Bringing up the client's network, and letting it request an IP.

As I said, the client may still get the same IP.  It depends on the DHCP
server configuration.  It may simply dole out the same IP because those
particular numbers were the next set that would be given out.

[tim at localhost ~]$ uname -r

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.

More information about the users mailing list