DHCP and printing (was Re: ntpq no longer working -)

[Tim]

Tim:
>> This probably means that your router also acts as a DHCP server for
>> your LAN (depends on what *yours* means by "on"), and will dole out
>> IPs to your LAN PCs.


Bob Goodwin:
> Yes, apparently so and yesterday my HP printer quit after I had done an 
> update [excluding cups] and caused a bit of a panic.  As it turned out 
> the printer was now residing at 192.168.1.2 instead of 192.168.1.3 where 
> cups expected to find it?  After working for several weeks it changed?  
> I set the HP set-up via the Firefox screen to fix it at 192.168.1.3 
> again.  My concern now is that 192.168.1.2 has always been my daughter 
> Ginette's MAC downstairs.  I haven't checked to see what address it has 
> now but fear that I may have created a mixed system which can result in 
> a conflict?  Or will the router's dhcp note the printer assignment and 
> avoid reusing it?  I may simply wait and see what happens unless someone 
> knows that I've created a problem.

DHCP is usually fine for clients, though can be a problem when you want
to do client-to-client actions (aka peer-to-peer, but nothing to do with
the file sharing p2p stuff on the net), and is often a problem with
servers.  It's also a pain for firewall and routing/forwarding rules.
But if your DHCP server is running fine, you won't get two things with
the same address.

DHCP doled out addresses are "leased".  After a while they expire.
Generally, a device will ask to have the same IP again when it
reconnects, even after the expiry period, and will generally get it
again if nothing else has been given it.  Generally, nothing else will
get it unless the system doesn't have enough spare IPs that it has to
reuse them.

You have some options, at least:

1. Set anything you need at a fixed address to have a fixed address,
either by ignoring DHCP, and statically assigning all addresses you want
to be fixed, or configuring your DHCP server to always give certain
things the same IP.  When fixing IPs, it's best to fix them outside of
the range the DHCP server doles out (e.g. let it dole out x.y.z.1 to
x.y.z.100 for the dynamic addresses, and you use the rest of the range
for statically set things).

2. Use an integrated DHCP and DNS that puts the names of each DHCP
configured machine into the local DNS server, then refer to everything
by name.  Then it doesn't matter if "printer" is at 192.168.1.2 or
192.168.1.34, because the "printer" name doesn't change.

3. Extend the lease period, so things that are turned off for a few days
have a better chance at getting the same address.

You'll find the DHCP and DNS servers in hardware devices are generally
rather limited in configuration options.  That's why I don't use them, I
do that on my server.

My own network uses fixed addresses (fixed one way or another).  I have
one box that isn't fixed so I can experiment, but the DHCP server is
mainly only for visiting computers.  They can plug in and work, without
requiring special configuration (usually).

> While on the subject of the hp6840 printer I have discovered that the 
> only way to get the proper driver for it is to install it from KDE.  It 
> offers that model number in its list of drivers and whatever driver it 
> actually installs works, installing from Cups/Admin [a generic HP 
> Deskjet] prints stuff from the browser that goes off the bottom and 
> right side of the page?  It seems strange that KDE has a more complete 
> set of drivers.  I discovered that by chance since I have never used 
> KDE, prefer XFCE and rarely use anything else.

I recently set up a HP photosmart printer for a friend.  It wouldn't
print anything from the web browser, it'd abort with a useless error
message.  Though it would print fine from other programs (e.g. like
Evolution).  It was set up the recommended way through, using the CUPS
local webserver interface.

Then, I tried removing that setup and using the system-config-printer
GUI tool in Gnome, and this time it worked.  There is some difference
between which drivers they both set up, but I do not know what.  Even
the CUPS printer test pages look a bit different (better colouring, and
a slight size change).

-- 
(Currently running FC4, occasionally trying FC5.)

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