SteveSpencer
Posts: 413
Joined: Thu Mar 28, 2013 9:19 am
Location: Nottingham, UK

[SOLVED] DHCP reservation no longer working

Wed May 13, 2015 8:21 am

I have a DHCP server on a Windows Server 2008 R2 machine which is configured to hand out reserved IP addresses to specific MAC addresses. I have successfully used this with a number of PiB and Pi2B machines, among others.

I ran apt-get update/dist-upgrade to move to the 05-05 release on a couple of the machines, and now they no longer get the reserved addresses. In one case, this isn't a huge problem (although inconvenient) because there is a monitor attached (actually a PiTFT, but it does show the IP address). In the second case it is less convenient, since it is headless.

Examining the UDP packets, there appears to be some additional data with the mac address forming the identifier in the DHCP request. Is this a configuration option somewhere that I can change and restore the original behaviour?
Last edited by SteveSpencer on Wed May 13, 2015 8:39 am, edited 1 time in total.
Steve S
No, I can't think of anything funny that won't offend someone if they want it to...

SteveSpencer
Posts: 413
Joined: Thu Mar 28, 2013 9:19 am
Location: Nottingham, UK

Re: DHCP reservation no longer working

Wed May 13, 2015 8:38 am

OK, I found it.

In /etc/dhcpcd.conf there is a section which turns on one or other of the options

clientid or duid

as the identifier. The clientid option is apparently off by default, which is just the MAC address, and the duid option is on by default, which is the MAC address, prefixed by some "random" 8 bytes of data, as shown in /etc/dhcpcd.duid

A quick edit of the config file and a reboot, and "all is as it once was", as the Guardian in "The City on The Edge Of Forever" said.
Steve S
No, I can't think of anything funny that won't offend someone if they want it to...

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