[Techtalk] serverless IP assignment?

[Raven, corporate courtesan]

Heya --

Quoth Malcolm (Mon, Feb 11, 2002 at 05:41:50PM -0500):
> I would be entirely unsurprised to discover several machines on the
> same powerbar that get turned off every night (and thus come up
> together the next day).

	[suppresses rant about putting 7 power-intensive devices off a
single power strip and then being shocked when there are weird performance
problems]

	Of course, I don't know how much your devices actually draw.  If
they're PC-sized, you're probably okay under most circumstances.  But
I've seen people put 5 Netras and two huge monitors off one power strip,
off a plug with older wiring, and it just gets ugly.  

> Machines are generally repaired in the field if at all possible (usually by 
> shipping the end user replacement parts and instructions).

	Under the circumstances you've outlined, Michelle's suggestion
sounds like a good solution for you.  Give it the biggest range of
bootable IPs you can to lessen the chance that you'll get duplicates
(before they even start looking for the DHCP server).  The random
backoff period would quite likely help with two boxes not deciding
they're the DHCP server at the same time.  

	Is the hardware for these devices (both legacy and current)
absolutely identical (same processor speeds, etc.)?  If so, the boot
time for each machine will be the same, and the random timer will be
really effective.  If not, then you may have another complicating
factor, and should design the backoff timer with that in mind.  Maybe
the fastest devices should have the random backoff between 1 and 10
[units], and the next fastest between 15 and 25 [units], and so on.
That way your fastest-to-boot devices will become the DHCP server, if
there isn't one already.

	If you're operating out of a /24 (255.255.255.0 netmask) and
your biggest network is 50 at the moment, you could easily assign 100
IPs in the bootable range and still have 154 available to assign to
machines.  That should be enough space for significant growth.

Quoth Michelle:
> What about this idea: Box starts up, it pings an address (say
> 192.168.1.1) and if that address responds, it get's it IP address from
> that box, which is the DHCP server. If it doesn't get a response, it
> waits a bit longer, tries again. If it still doesn't get a response,
> it then calls itself 192.168.1.1 and starts up the DHCP server.  You
> might incorporate a random wait period, so that if two servers were
> turned on at the same exact time, they would be unlikely to start up
> their DHCP servers at the same time.

	That sounds eminently sensible to me.  And that way, you
eliminate the problem of a broken box being pulled off the network,
keeping its address, and screwing things up when it's plugged back in.
 
> See above, this is not an unlikely situation as it's more than just power 
> cuts, but end users turning the machines off (generally by hitting the power 
> switch, which is a whole other set of problems).

	Journaling filesystem?  [grin]
 
> I was hoping to use the 10.x.x.x, but every box has to be able 
> to talk to the third part machine which is netmasks at 255.255.255.0.

	You can still do that.  Use 10.1.1.x/24.  If you are wanting
your boxes to all talk to each other without benefit of a router,
they'll have to be on the same local subnet, and so you would have to
number them out of whatever subnet the third party box is using.  (So if
you don't control that, then you'll have to set your network mask to
whatever network they're using.)  But if all you need is any /24, you can
carve those out of the larger 10.0.0.0/8 if you want to.
 
> I'm not, there isn't any. Each location is a self contained network. (Not 
> entirely, each machine also has a modem it uses to 'dial home' as it were, 
> but no routing is needed between the internal and external networks at this 
> point in time).

	Okay.  Are you ever going to need that, in the foreseeable
future?  If you are, might as well build it in now and save yourself an
upgrade later.

Cheers,
Raven
 
"What happens if you boot without the boot disk?  Where does it die?"
"If I boot without any boot diskette, it just boots into Windows."
  -- me and Katie, regarding OS problems