[NTLUG:Discuss] DHCP

[David I S Mandala]

Terry,

That is an accurate statement no matter what type of computers/devices 
are attached to the network. Things will get very confused and not work, 
especially if you have network switches (which most people have) vs hubs.

That said, there is no reason to ever issue "static" static IP's to any 
device on the network, with the exception of the DHCP server itself. Use 
the DHCP server to hand out IP addresses that remain static to a machine 
based upon the machines MAC address. Yes if you switch a machines 
Ethernet card you will need to update the DHCP config file but if all 
addresses are handed out via DHCP it's easy to expand or switch your 
network by configuring a single machine (the DHCP server).

This is also very handy since Windows PC default to DHCP out of the box. 
All you need to grab is the MAC address and you can configure the DHCP 
server. Then once the PC is plugged into the network it will get a 
"static" IP via DHCP. You don't need to make any changes on the Windows PC.

You can cheat if you like, have a small pool of IP address's available 
and you can look in the log and when you plug in a new machine it will 
get an address from the pool, you can then see it's MAC address and 
assign that MAC a permanent IP address and the next time on the network 
it will get that address from then on.

There are other tricks you can do like put a log parser on the DHCP log 
and have it notify you via email anytime a new device pops onto the 
network. That way if someone has attached a device to the network you 
will know about it.

Cheers,

David

Terry wrote:
> Is this an accurate statement (pertaining to a Linux DHCP server
> presiding over [mostly] MS PCs)?
>  
> "Having a system with a static IP assignment that is inside the range
> of IPaddress' used by a DHC P server is not acceptable.  Reason being:
>  If a new computer comes on-line, it may be issued that particular
> IPaddress, and if so, there will be a problem.  This may never happen
> on a small network. If there are only a handful of computers on the
> network (half a dozen or so), you may never run into this sort of
> problem.  BUT, if and when the network grows and gets to be fifty or a
>  hundred strong, sooner or later, this problem will rear it's ugly
> head.  A computer will come on-line and be issued an IP address that
> has been set as a static address to another computer, .. . and then,
> later on, that other computer with the static IP address will come
> on-line, and at that point they will both compete for access that only
> one can have. During the competition neither of them will get any
> access and only when one gives up will the other gain any bandwidth or
> access to any outside networks. Fixed IPs should _only_ be assigned to
> IP address that are outside the range used by the DHCP server."
> 
> _______________________________________________
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David Mandala <davidm at them dot com>
www.them.com/~davidm Public Key id: 45B2D952
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