DHCPv6 logs filling root volume with renewal requests from my printer

[skruger]

I ran across an interesting problem today as I was trying to figure out why my opnsense firewall had died. It went unresponsive and after rebooting it I found the root filesystem full. As I investigated I determined that there were log files in /var/log/dhcpd that were 5-7GB in size for my little home network with less than 40 devices. I removed the largest files from the last few days and things started working better.

I started tailing /var/log/dhcpd/latest.log to see what was being written and it was writing the same thing over and over so fast that the sequenceId value just looked like a counter in an infinite loop showing the same 4 lines over and over.

<190>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184686"] Renew message from fe80::42b0:34ff:fe9f:47de port 546, transaction ID 0x250FF600
<190>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184687"] Reply NA: address 2602:3f:e615:<redacted> to client with duid 00:03:00:01:40:b0:34:9f:47:de iaid = 2 valid for 7200 seconds
<191>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184688"] Reusing lease for: 2602:3f:e615:<redacted>, age 650 secs < 25%, sending shortened lifetimes - preferred: 1, valid 6550
<190>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184689"] Sending Reply to fe80::42b0:34ff:fe9f:47de port 546
<190>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184690"] Renew message from fe80::42b0:34ff:fe9f:47de port 546, transaction ID 0x2C7EB000
<190>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184691"] Reply NA: address 2602:3f:e615:<redacted> to client with duid 00:03:00:01:40:b0:34:9f:47:de iaid = 2 valid for 7200 seconds
<191>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184692"] Reusing lease for: 2602:3f:e615:<redacted>, age 650 secs < 25%, sending shortened lifetimes - preferred: 1, valid 6550
<190>1 2024-06-16T08:39:12-06:00 OPNsense dhcpd 35452 - [meta sequenceId="184693"] Sending Reply to fe80::42b0:34ff:fe9f:47de port 546

It didn't take long to figure out that the link local address was for my LaserJet Pro MFP M277c6 which doesn't have any IPv6 configuration options on its UI.

As I was trying to figure out how to just ignore this device I decided to try assigning it a static DHCP6 reservation. After configuring a reservation for it with an IPv6 address and a description it was able to take its address and start working normally without churning through the same 4 renewal steps over and over.

I'm guessing this was a problem caused by a badly behaving printer, but it was a strange enough problem I wanted to make sure what had happened and what seems to have resolved it got recorded somewhere in case someone else runs into a similar issue.

Versions:
opnsense 24.1.8
isc-dhcp44-server 4.4.3P1_1
Not using kea dhcp server

I haven't been on opnsense 24 for long, I upgraded from 23 series in the last 2 weeks.