Dhcp lease client hostname missing (with 2.3)

cmb

For me, this only seems to happen for devices connected wirelessly.

I doubt it's wireless-related. dhcpd has no way of knowing how a device is connected, a wifi lease looks exactly the same as a wired lease.

Thanks for confirming the behavior hasn't changed in 4.3.4.

This probably needs to be escalated to the ISC dhcpd list to hopefully get feedback there.

AsgardianFW

cmb,
Who should do the escalation? One of us? You?

cmb

I'm not going to have time to see it to resolution with only 2 weeks left. If one of you can push it along, that'd help get to a faster resolution (I hope). Otherwise someone should get to it at some point.

vynce

Thanks Chris. I've posted to the dhcp-users mailing list. Hopefully they have some suggestions :)

cmb

@Vynce:

Thanks Chris. I've posted to the dhcp-users mailing list. Hopefully they have some suggestions :)

Thanks, I followed up on that thread with some specifics as well.

zxvv

Are you synchronizing two dhcpd servers that are doing dynamic dns registration?

I believe there is a known limitation in the isc-dhcpd sychronization, in that it transfers the lease between dhcpd servers, but fails to transfer the host name.

vynce

Thanks for the heads up on that sync issue. In my case it's just a super basic configuration – no redundancy, syncing, or anything.

vynce

Shawn Routhier (ISC DHCP lead engineer) suggested adding "dhcp-cache-threshold 0;" to dhcpd.conf to disable an optimization that allows dhcpd to skip updating dhcpd.leases when a client requests an updated lease after less than 25% of the lease time.

Here's how I made that change in case anyone else wants to give it a try. Not sure if it's the best way, but the setting has been added to dhcpd.conf at least.

Diagnostics -> Edit File.
Paste "/etc/inc/services.inc" in the box and click Load.
Add "dhcp-cache-threshold 0;" on line 541. There's another location around line 1285 for dhcpdv6 if that applies to your configuration.
Click save.
Services -> DHCP Server.
Click save to regenerate dhcpd.conf and kick dhcpd itself to reload its config.

Now to wait and see what happens :)

AsgardianFW

My setup is also pretty simple. The only non-default settings I have are some static leases and the default lease time is set to 86400 (24 hrs). The longer lease time makes is easier to see the problem because the hostname comes back after a lease renewal. The default time of 2 hours somewhat hides the hostname issue unless you're really watching it.

I have made the suggested change to disable the optimization and I'll report back within 24 hours.

AsgardianFW

So far this works at my smaller office. I'm deploying the "fix" to a larger office for additional verification.

vynce

This workaround fixed my two installations as well :D. I'll reply to the dhcp-users mailing list and hopefully we can come up with a proper fix for the next version of isc-dhcpd.

cmb

I implemented that workaround for 2.3.2, since disabling the cache threshold won't have any impact on our users' use cases and it does appear to avoid the root cause problem.

Thanks for getting the ball rolling on that one Vynce, had I realized a workaround would have come that easily, I'd have done so some time ago.

AsgardianFW

Thanks Vynce for championing this effort with ISC.

Thanks cmb for incorporating this into the next version. I wasn't looking forward to remembering to patch this in manually after every upgrade. I wish you the best of luck for whatever is next for you.

vynce

Thanks Chris! I've opened a bug ticket in the isc-dhcp project to address the root issue: [ISC-Bugs #42849]. Their bug tracker appears to be closed to the public due to privacy concerns. Do we need to try and get some pfSense project email address added as a watcher? Not sure if you intend for the workaround to be reverted when the root issue is fixed…

cmb

Thanks Vynce. Once it's fixed, please start a new ticket at redmine.pfsense.org to revert that change, as it would be preferable to go back to the default there once it doesn't break other things.

vynce

Sounds good, will do.

vynce

Just a heads up that a patch for this issue has been committed to master in the isc-dhcp project and will be included in the isc-dhcp 4.3.5 beta. I will create a pfSense ticket to pull in isc-dhcp 4.3.5 final once it is released and revert Chris's workaround. I might try to build a pfSense-compatible dhcpd that includes this patch to verify the fix.

driiper

I upgraded to 2.3.2 but are still having this issue with some of my boxes. I run a proxmox (KVM / LXC ) hypervisor. While the KVM boxes keeps their hostname in the dhcp records. The LXC boxes loses it after a while.

Do i have to do anything to apply this fix to a upgraded system (2.3.2)?

vynce

You shouldn't have to do anything AFAIK. You can verify that the workaround is in place:

Diagnostics -> Edit File.
Paste "/var/dhcpd/etc/dhcpd.conf" in the box and click Load.
Verify that dhcp-cache-threshold 0; is listed in the file.

vynce

isc-dhcp 4.3.5 was released today and includes the fix for this issue. I've opened a new bug ticket to track upgrading to 4.3.5 and revert the workaround that Chris added.