Dhcp lease client hostname missing (with 2.3)
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pfSense 2.3.1 is running ISC DHCP Server 4.3.3-P1. Looking through the 4.3.4+ release notes, the only item that stood out to me was:
- Added the lease address to the end of the debug level log message emitted when an existing lease is renewed within the dhcp-cache-threshold. Thanks to Nathan Neulinger at Missouri S&T for suggesting the change. [ISC-Bugs #40598]
There are quite a few bug fixes, but it's difficult to tell if any of them are related to this issue.
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Added a bug ticket for this issue, as there definitely is something to it.
https://redmine.pfsense.org/issues/6589 -
Vynce, perhaps you're on to something. I can add a little more evidence to the pile. For me, this only seems to happen for devices connected wirelessly. Although, I will confess that almost all of my wired devices have a static lease in DHCP. I do have 1 Windows desktop that is permanently connected via wire and has a dynamic lease. It has never exhibited this problem. I also have 1 Windows laptop that is connected wirelessly from time to time and I've never seen it lose its hostname (but the laptop isn't on all the time). 2 data points may not be enough to draw a proper conclusion, but so far the problem seems to target Android and Apple phones and tablets connected wirelessly (I have 6 different models of these devices so it doesn't appear model specific). At one point I thought it might be related to roaming between access points on my wireless network, but I did observe a loss of hostname of my phone while I was holding it in my hand sitting at the computer watching hostnames (so while I'm not 100% sure, I don't think it changed access points).
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Please don't hate me for this, but I installed OPNSense (16.7 RC1) in a small, non-essential location (with 2 iPhone users) because it has ISC DHCP Server 4.3.4. I just confirmed that it, too, loses hostnames so the problem isn't addressed in the newer dhcp version.
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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.
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cmb,
Who should do the escalation? One of us? You? -
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.
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Thanks Chris. I've posted to the dhcp-users mailing list. Hopefully they have some suggestions :)
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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.
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Thanks for the heads up on that sync issue. In my case it's just a super basic configuration – no redundancy, syncing, or anything.
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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.
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Diagnostics -> Edit File.
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Paste "/etc/inc/services.inc" in the box and click Load.
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Add "dhcp-cache-threshold 0;" on line 541. There's another location around line 1285 for dhcpdv6 if that applies to your configuration.
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Click save.
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Services -> DHCP Server.
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Click save to regenerate dhcpd.conf and kick dhcpd itself to reload its config.
Now to wait and see what happens :)
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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.
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So far this works at my smaller office. I'm deploying the "fix" to a larger office for additional verification.
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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.
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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.
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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.
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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…
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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.
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Sounds good, will do.
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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.
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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)?
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You shouldn't have to do anything AFAIK. You can verify that the workaround is in place:
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Diagnostics -> Edit File.
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Paste "/var/dhcpd/etc/dhcpd.conf" in the box and click Load.
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Verify that dhcp-cache-threshold 0; is listed in the file.
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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.
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The workaround does not seem to be working for DHCPv6.
I verified that the workaround is in place in /etc/inc/services.inc . It appeared in 2 locations in the file.
Clients are ubuntu 14.04.3 LTS and 16.04 LTS.
On this version:
2.3.2-RELEASE-p1 (amd64)
built on Tue Sep 27 12:13:07 CDT 2016
FreeBSD 10.3-RELEASE-p9 -
@rsq:
The workaround does not seem to be working for DHCPv6.
In DHCPv6, the client does not provide its hostname to the DHCP server. The only form of identification is the DUID, a unique identifier that is generated by the operating system when the computer is set up. The only way a hostname is present under DHCPv6 is if it's a static entry, where you can enter a hostname yourself.
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I am on 2.3.3-p1 and have issues with missing hostnames.
Found this threat and checked if dhcp.conf has the "dhcp-cache-threshold 0;" and it doesn't.
Is this still needed or should this be fixed without the workaround?
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The workaround is no longer needed since the root issue was fixed in isc-dhcp 4.3.5, which is included in pfSense 2.3.3. That's not to say there isn't some other issue causing missing hostnames, but I haven't seen a regression of this specific issue in pfSense 2.3.3.