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Re: changing DHCP server used to assign IP address to laptop

On Thursday, 24.03.2005 at 10:58 -0400, Tom Weller at Ambassador
Computers wrote:

> > > How do I direct my laptop to a particular static IP address for
> > > obtaining DHCP leases? I set up the laptop at home, which has a
> > > direct ISP connection (cable modem), but when I bring the laptop
> > > to the office I need to get an IP address from a router, not
> > > directly from the ISP provider.
> > 
> > Is the cable modem interface a different physical interface from
> > what you use "at the office"?  Or are they both accessed from your
> > laptop's ethernet connection?
> > 
> > "How do I direct my laptop to a particular static IP address for
> > obtaining DHCP leases?" is a very strange question.  The whole point
> > of DHCP is that it doesn't try to connect to a particular IP address
> > (until you're assigned an IP, you can't do that anyway).  A DHCP
> > client request involves sending a network broadcast to the local
> > network segment and something will respond (hopefully) and offer you
> > a lease.
> > 
> > If setting each interface you use to be "get address via DHCP"
> > doesn't work, then something is wrong with the DHCP *server*.
> Well, I notice during boot that the DHCPDISCOVER is always bound to
> the IP Address of the ISP provider, which was the DHCP server for the
> set up at home.  I'm assuming that because the 24 hour lease was still
> in force that the DHCP client still refers to that server.

Well 'bound to' is a rather strong term - it will note the IP address of
the server it last got a lease from.  If it is able to renew that lease,
it will do so.  If not, it will broadcast for a new lease.  The same
server *may* be the one to provide the new lease, it may not.

> By the way I do have internet access at the office, because it is the
> same ISP as at home, but I do not have access to the office network. 

I don't understand this sentence - do you mean that you are physically
connected to your office's network, but that you cannot 'see' anything
on it?

Does your office network have its own DHCP server?  If your laptop is
contacting your ISP's DHCP server to renew its existing lease, then,
given that you are now in a different location, the DHCP server should
deny that renewal, deny any further attempts to get a lease from it, and
then your laptop should try to get a lease from the office DHCP.  If
that's not happening, then your office's setup is wrong.  Your office's
firewall/gateway/whatever, should not allow DHCP requests to pass anyway

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