Strange DHCP issue

How would that help the connection problem at work? Just curious.

Ok... I think there is some misunderstanding...

Let me clarify... The company does NOT have wireless... And in fact when the problem appeared this morning I turned wireless off.

At home I have both wireless and wired so I can move about the house. Both end up on 192.168.168.x. Regardless of if I'm wired or wireless DHCP at home hands out an address, usually 192.168.168.207 or so since I have other machines (wife, kid, printer, etc).

So with wireless turned off the problem came up in the following way:

The MBP was working fine at home. Did the superduper backup. Found it asleep. It was fine otherwise.

Come to work and suddenly getting IP conflicts. Nothing that I could see changed and this setup had been working perfect for probably 6 months.

I could sit and watch in network prefs when set to DHCP and see it pause, flash up a DHCP address of 192.168.168.207 from a router of 192.168.168.1 (mine at home is at 192.168.168.250). Then give the conflict message and repeat the following ad infinitum.

I rebooted a windows machine on the same switch as me to see if it was something with the company DHCP servers. No problem. It came up with a perfect company DHCP address.

As I said I toggled between manual, manual DHCP, DHCP and I rebooted several times. All same problem.

I did find a temporary fix. After booting my MBP I let it come up with the conflict then I went and powered down my switch and repowered it. Upon power up my MBP got a company DHCP address.

At first I figured my switch had barfed but the windows machines on that same switch work fine. For grins I rebooted my MBP (hoping the problem was now fixed). On boot I again got the conflict. Power cycling the switch again allowed me to get a DHCP address from the company server.

Strange. The wierd thing is this has been working FINE for 6 months. I tried a NVRAM reset with no luck. Didn't have much hope but figured it was worth a try.

So I'm running but still very puzzled. It acts like somewhere stored in my MBP network configuration is a perference for using a DHCP server on a 192.168.168.x LAN.

Like I said, I've NEVER had it do this before and I can't understand why it seems to perfer this now. I also don't understand why power cycling my switch seems to fix this.

What I think is happening is like I said we have some "test units" of the machines we make running around the company LAN. There are probably 10 of them.

These machines (test units" consist of a machine, a small server, and a router. Because these machines get installed in companies that are wary about network use we ship them with a small router. The router is configured to give out DHCP addresses ON ITS SMALL LAN PORT ONLY of 192.168.168.100-150. The server on this small router is statically configured to 192.168.168.5.

They plug the WAN port of these routers into the company LAN. The WAN ports are configured to get a DHCP address from whoever they connect to. The router is setup to provide ONLY outgoing rules from the machines on the small LAN to the outside world. No incoming connections are allowed. This is how we make company IT managers feel safe yet we still allow our units to issue outbound connections for diagnostic purposes.

Like I said there are probably 10 of these "setups" running on our LAN a the company and these have been doing so for probably 2 years.

They way they are setup I should not be able to get to the DHCP server in ANY of these small routers because it is setup to only respond to DHCP requests on it's 4 port LAN.

I'm not sure but there may be a way that it can do DHCP over it's WAN port and perhaps some one has futzed with one and it is doing so. That would be strange to say the least.

Anyway my MBP running OS X normally plugs into the company LAN and I get an address of 135.16.0.xxx. This has been working for a very long time. When I take it home the DHCP works there too and gives me an address in the 192.168.168.xxx range. Again for a very long time no issues.

Whether or not someone in the company has issued a manual address of 192.168.168.207 should be meaningless. My MBP is configured to get whatever address the company DHCP server hands out.

When connecting at the company I normally DO NOT get an address in the 192.168.168 range. I always get a company class B I think address of 135.16.0.xxx. As I said this had been working perfectly for MONTHS!

What seems to be happening is somewhere in the company there is a DHCP server that seems to be at 192.168.168.1. When my MBP boots it seems to perfer connecting to this one rather than the company server.

This has never happened before and I can't figure out where in preferences you can set which DHCP server you connect to. I always figured you couldn't have more than one on a LAN.

If you do how does the MBP decide which to use?

Also why does powercycling my switch seem to fix it?

Jojo...

thanks for taking all the time to respond. I appreciate it.

mcseman, I think you are right... it is some how for some reason prefering the DHCP located on 192.168.168.xxx But what still does not make sense is ok so it picks that one. Why does the address it gives me conflict? I guess there could be a manually entered 192.168.168.207 on the lan but I would tend to doubt it.

Strange. I'll go ask IT

It seems the DHCP client favors any last address it was given.