Re: Two elementary questions on LANs


This is very interesting information. I have a couple of additional
questions that you may be able to help me with that I think are
applicable to this thread. Please see below:

---------- Forwarded message ----------
From: Ed Greshko <Ed.Greshko@xxxxxxxxxxx>
To: Community support for Fedora users <users@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 17 Jun 2011 06:48:02 +0800
Subject: Re: Two elementary questions on LANs
Some additional information regarding DHCP.....

As I mentioned, the lease information is retained by both the client and
the server.....

Let's assume that this is not the first time the client has acquired an
IP address from the server.  Let's also assume that the interface is
currently down and a file exists in /var/lib/dhcpclient for the
interface in question.

Now, you enable the interface and the following happens....

1.  The dhcpclient checks the file to see what IP address it was last

2.  The client then sends out a UDP broadcast with source address of and destination of (a broadcast request)  It
will be a message type of DHCP Request and the packet will contain the
previous IP address it is requesting.  It will also have a "transaction
ID" in the packet.

I have desktops and laptops on my local LAN that each dual-boot with
F15 and Windows and each have a wired and wireless LAN connection. My
router acts as the DHCP Server but doesn't have the capability to
assign a pre-defined IP address to each machine based on its MAC
address. Besides, I would like each machine to have a different
address assigned depending on whether it was running Fedora or Windows
in a given instance. I don't want to assign fixed IP addresses to the
clients - I want them to get the addresses from the server so that
they don't have to be reconfigured if they go off of my LAN and onto
another (e.g., the laptops). But I would like to set them up to each
request a unique IP address from the server and to identify themselves
differently depending on whether it is the wired or wireless
connection such that they are very likely to get what they request.
(The reason I want this IP address stability is because I use Backuppc
to back each up and now the volatility of their IP addresses is making
it so that that doesn't work too well. The volatility is caused by
other more transient devices getting on and off the network and
causing the reassignment of previously assigned addresses to not occur
very often.)

3.  The server will respond.  The source address will be its IP address
and the destination will be Another broadcast.  The
response will have the same "transaction ID" as the request and the
client will match these to know the broadcast message is meant for it.

You are done....

If a file in /var/lib/dhcpclient does not exist for the interface the
procedure is a bit different....

If this file does exist, can I simply edit it to put the IP address I
want assigned to each LAN interface of each machine into it and thus
achieve what I want?

Can I simply put in a different 'option host-name' value into the
wired vs. wireless files in this directory to achieve my goal of
distinguishing them (e.g., HPfedora vs. HPfedora-wl) for a given
machine or OS (e.g., HPVista vs. HPVista-wl)?

Or are there other configuration files where I should put this
information that will cause the client to send out the DHCP Request
with the IP address and host-names that I want?

I would be grateful for your comments.

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