honda4life
Posts: 75
Joined: Thu Mar 15, 2012 7:27 pm

Strange behaviour DHCP

Fri Apr 26, 2013 5:34 pm

Hello everyone,

Mu pi is becoming the most annoying pi in the world... :mrgreen:
I've started with the latest image from the website about 2 weeks ago (time to upgrade one of the very first releases of of the softfp OS).
Okay, run a portable DHCP server on my home computer.
Connected to the pi over SSH, did most of the configuration and wanted to test on my home network.
This was working for a short time, after a while connection lost, but this could be a connection issue.
So back to the computer... a bit problems but it worked.
Did some extra configuration, played with some iptables (but there aren't stored after a reboot).
The next day, tried again on the home network,... no success.

...

To make the story a bit shorter, when I look into the DHCP log on my computer, it asks an old ip, from the home network.
DHCP rejects, because of different range and propose a new IP.
> Where old IP is saved in the pi? This may solve the problem.

To make it even more confusing:
Tried an old router, plugged in the pi, and the computer I can reach the pi, but time between username prompt en password prompt seems very slow.

Back to computer, not working dhcp, but pi request ip from old router...

Who can help me solve this problem please, a lot of work has been done to upgrade.

obcd
Posts: 917
Joined: Sun Jul 29, 2012 9:06 pm

Re: Strange behaviour DHCP

Sat Apr 27, 2013 7:21 am

Back to computer, not working dhcp, but pi request ip from old router...
DHCP doesn't work like that. If a network interface is set to dhcp, the device will broadcast a dhcp request. A dhcp server on the same subnet will provide a valid dhcp ip adress to the device.
DHCP servers tend to hand out the same DHCP ip to the same device every time, based upon the device MAC adress. Maybe that's the information you are seeing.
Your login and password prompt appearing slow is a totally unrelated problem and can be fixed with a tweak to a configuration. You could try to google for that problem as it's not typical for the Pi. It came up in this Forum as well together with the solution.
You can only have one DHCP server on a subnet. Could that be your problem?

honda4life
Posts: 75
Joined: Thu Mar 15, 2012 7:27 pm

Re: Strange behaviour DHCP

Sat Apr 27, 2013 7:40 am

That's nothing new to me, maybe my information wasn't clear.

I have another pi, plugged in the SD card... no problem at all.
When I plugged the SD card from the other pi, in the bad pi, the same problem.
I have also a third SD card that worked in the bad pi > same problem.
I think my ethernet is broken, why it works on the old router (not connected to home network) is not clear.
Maybe gigabit ports have a stronger/better signal or it's just a better router?

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