DHCP not farming out address, randomly

[synaesthesia]

Bit of a strange one that I'll run past you. It's a site I only visit on a fortnightly basis so excuse any vagueries, but thought asking might give me some ideas to try.

The setup.

40 wireless (RM) laptops.
Circa 20 desktops
2 servers, admin and curriculum (CC3).
Wireless is non managed, supplied by Dlink AP7100 access points
CC3 server dishes out DHCP (although for some reason it was on a split load, which I today changed) and DNS.

The problem.

Some, but not all of the laptops are refusing to pick up an IP address from the CC3 (DHCP) server. The setup's are identical. I've just added 5 brand new RM mobile one widescreen laptops, built identically. 3 pick up addresses, 2 don't.

I've flushed all relevant caches, restarted the access points, flushed the DHCP allocation list. Manually set the CC3 server as the gateway (although ultimately the router will be the gateway) to force detection as the DHCP server. Checked all firewalls are disabled.

As briefly mentioned, both the CC3 and admin servers ran DHCP on a split load, CC3 doing a small amount (50 IPs) and the admin doing the rest (100). That's a setup that RM (at least used to) recommend which harks back to the old days of NT kit, so I removed that and set the cc3 server to handle them all. That didn't cause the problem, just part of my attempts to fix.

So, any input gratefully appreciated

Nothing's doing the trick, and I'm fresh out of brain-juice. There's quite possibly

[leco]

Some thoughts:
Is there a possibility that the DHCP has temporarily run out of addresses?
Have the laptops been connected to the wired network as well as the wireless? Sometimes I have to put laptops onto the wired network before they pick up IPs wirelessly.

[synaesthesia]

Yeah, tried a few over cables, they pick up addresses fine over that, ping the router/gateway, access points and servers without issue.
Thought about the address allocation - checked up on it whilst there yesterday to find 60 day IP address leases (!) which is another RM "standard" which I'm led to believe is another archaic setting from the "good old days". Either way, there's still a good 80 addresses free for lease, but as mentioned I'd cleared the lease database/cache anyway :/

[leco]

Issue I had was the DHCP scope had the wrong settings - legacy from when a previous server was operational. Most of the desktops coped, they somehow re-routed or just carried on using their old IP. The laptops wouldn't/couldn't do this - solved when I found the scope setting and changed it to a server that actually existed.

Could it be a permissions thing? What do the event logs on the laptops have to say when attempting to gain an IP?

[synaesthesia]

Don't think so, as sometimes a unit will turn on and magically get an IP and what not. Will certainly double check though.

DHCP scope option errors - hmm I did suspect there might be something untoward in there but the options therein felt very unfamiliar. Noteably there's an option in there about the DNS server/suffix or something, which was set to the FQD rather than just "Local" which I noted was the working setting from other sites I've been at. So that's also a suspect.

Cheers for the input

[leco]

Something else to consider then would be the location of the laptop in terms of access points. Can they actually connect to one and not another? Are there contention issues with other machines connecting at the same time.

Issues that crop up all the time, every time are far easier to track down. When "it" only happens sometimes is when solutions get harder to find. I'll keep thinking.

[synaesthesia]

At the time of trying to solve this, I had all the laptop trolleys in the server room with me with the AP patched right in next to it, so definitely not contention. Have run a survey round the site and it's already set up on the most appropriate channel, and there's no interference from anything else around :/

[FragglePete]

Have you tried just setting a static IP address on the wireless card of a laptop to see if that works ok and access the network correctly? Would rule out a problem with the wireless cards I guess.

Pete

[synaesthesia]

Yeah, but had no throughput on them. Too large a number to be a wireless issue, but something I'll need to check definitely.

[funkymunky]

Yeah, but had no throughput on them. Too large a number to be a wireless issue, but something I'll need to check definitely.

When you say no throughput do you mean you can't access the network at all when set statically? If so then it doesn't appear to be a DHCP issue it looks more like a layer 2 issue, if that's not what you meant and you can access the LAN you just can't obtain a lease the first thing I'd do is run tshark/Wireshark on both the client and the DHCP server (or mirror the switch port and monitor that if easier/necessary) to see where the packets are actually getting to. Also what's the connectivity between the APs and the DHCP server? Any switches in between that are doing any filtering or DHCP snooping?