DHCP not handing out spare leases

Hi All,

This is a fairly urgent problem so i'm hoping I can get some helpful tips here.

Our network uses Win2k3 DHCP & DNS (both on the same server). The network configuration is 172.18.0.0/22 (Subnet of 255.255.252.0).

We have DHCP set to hand out leases in the scope 172.18.1.10-172.18.2.250

Except when the lease's hit 172.18.1.254, it wont hand any new ones out and hand's out old ones. Meaning when the machine it did belong to connects, we get IP conflicts.

I've checked everything I can think of but cant find anything wrong DHCP wise... it sucks cause everything is coming to a halt!!!

We're only just having the problem now because we've started to add new machines to the network (bringing the total above the 172.18.1.x number available).

Weirdest thing is, DHCP says that it's got ~ 50% free leases... so why isnt it handing any out in the 2.x range?!

I'm thinking about altering the subnet to 255.255.0.0 to see if it resolves it... but obviously thats alot of work. Help please!!!

Anyone? :(

Have all of the reverse lookup zones got a SOA (start of authority)?

Also, since were spread over 3 DCs we have an NS record for each server in each.

Is the correct subnet mask definitely set on the server's network interface?

Quote:

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Originally Posted by james_yale

Is the correct subnet mask definitely set on the server's network interface?

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Yup

Hmm, i'll checkout the SOA stuff... may well be that!

Nope:( all lookup zones have the correct SOA records :(

Try splitting it into two blocks.

172.18.1.1 - 172.18.1.254
172.18.2.1 - 172.18.2.254

then exclude

172.18.1.1 - 172.18.1.10
and
172.18.1.250 - 172.18.1.254

also

172.18.2.250 - 172.18.2.254

2k3 DHCP wont allow me to add a second scope in the same subnet. It says "THe address range and mask conflict with an existing scope"

Which is a downright lie :P

Won't you have to edit the scope first, then add the second?

Did. Even took the brave/stupid/smart (delete as appropriate) move to delete the zone totally.

Gulp.

Mmm... guessing it wants .24 subnet. Could try the one scope:

172.18.1.1 - 172.18.2.254

exclude

172.18.1.1 - 172.18.1.10
172.18.1.250 - 172.18.1.255 (or is it 4)
172.18.2.250 - 172.18.2.254

Wouldn't say about using .24 / 255.255.255.0. I'll let someone else say\try that - Don't like the whole issue of routing etc ;)

Well my current thoughts at the moment are to do one of the following:

a) change the entire network subnet to 255.255.0.0 - But if DHCP wont give out leases in the same subnet for a /22 range... which this make any difference?!

b) All of our switches support vlans... segregate our network and use vlans. Zone the entire school out and then give /24 subnets to each zone.
(Problem is i've never really played with vlans... do i risk it?!)

c) Just found out, even with DHCP being on a single range now of 1.1 to 1.250, it reports 92 addresses free... yet DHCP is still handing out addresses which are in use. Makes me think there's another problem somewhere.

d) build up an old box as a linux machine and setup dhcpd on it and use that.

b)
VLANs really is something for the summer holiday when no-one is using the system.

We had similar situation before and after hours of troubleshooting we found out that one of our staff setup his own home router with DHCP service running in his classroom.
It was a nightmare!

OK, I'm curious here: why are you using 172.18.x.x and not 172.16.x.x?