[Dnsmasq-discuss] Tracing a dnsmasq bug - hot loop - possibly DHCP6 lease management

Sun Feb 23 07:05:15 UTC 2025

Hello,

I am tracing an issue where dnsmasq 2.86 appears to get stuck in a loop
using all compute resources for the core it's on, and becomes unresponsive
to DHCP4, DHCPv6 and DNS requests.  I am working on replicating the
problem, and want to check to see if anyone on this list has seen the
behavior before --

-- Details --

On the local LAN I am seeing 3 devices in DHCPv6 that are requesting IPV6
addresses every 10 minutes, even though their expiry time is advertised as
8 hours. I will have some difficulty finding the exact devices.  It appears
the DHCPv6 lease file continues tracking all of the leases on this openwrt
based router.

A subset of these tracked requests are here, from the lease file -

1740156067 1484488511 2600:4040:a92e:2700::ffcd *
00:03:00:01:f0:09:0d:cb:26:08

1740156067 1484488511 fd30:fc9a:a298::f8a3 * 00:03:00:01:f0:09:0d:cb:26:08

1740156067 1375367042 2600:4040:a92e:2700::ffcc *
00:03:00:01:f0:09:0d:cb:27:52

1740156067 1375367042 fd30:fc9a:a298::f8a2 * 00:03:00:01:f0:09:0d:cb:27:52

1740155562 1744997917 2600:4040:a92e:2700::ffcb *
00:03:00:01:f0:09:0d:cb:26:08

1740155562 1744997917 fd30:fc9a:a298::f8a1 * 00:03:00:01:f0:09:0d:cb:26:08

1740155561 729442040 2600:4040:a92e:2700::ffca *
00:03:00:01:f0:09:0d:cb:27:52

1740155561 729442040 fd30:fc9a:a298::f8a0 * 00:03:00:01:f0:09:0d:cb:27:52

1740155561 1831382606 2600:4040:a92e:2700::ffc9 *
00:03:00:01:f0:09:0d:cb:25:b0

1740155561 1831382606 fd30:fc9a:a298::f89f * 00:03:00:01:f0:09:0d:cb:25:b0

1740155018 995327705 2600:4040:a92e:2700::ffc8 *
00:03:00:01:f0:09:0d:cb:25:b0

1740155018 995327705 fd30:fc9a:a298::f89e * 00:03:00:01:f0:09:0d:cb:25:b0

So, this is 48 entries (identical) in the dhcpv6 lease file per host that
does this.  There are 2 entries, per host (96 entries) .. and there are 3
hosts on the LAN doing this -- bringing the entries to 288 tracked leases,
excluding the IPV4 leases too.

My dnsmasq config file is attached ( dnsmasq-configfile.txt ).  The only
parameter I imagine is related :

   dhcp-range=set:lan,192.168.2.40,192.168.2.254,255.255.255.0,8h

Notably - this is not a DHCPv6 setting, but it *does *show the 8h lease
time I am seeing in the DHCPv6 leases , AND the parameters here have a
limit of 215 addresses these hosts are pushing (the same) number of leases
over 288 within an 8hour span.

Has anyone seen this before ?  Why are the IPv6 leases not replaced in the
lease file when the same DUID requests addresses well before the end of the
IPv6 lease time ?

*Bonus* -- I've attached a pcap file for the DHCPv6 requests I think could
be central to this problem.  These packets arrived much later of course,
well after I've experienced this problem, but may give us some insight to
what's happening.

Thank you,
Bryant Eadon
ᐧ
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# auto-generated config file from /etc/config/dhcp
conf-file=/etc/dnsmasq.conf
dhcp-authoritative
domain-needed
filterwin2k
localise-queries
read-ethers
enable-ubus=dnsmasq
expand-hosts
bind-dynamic
local-service
dhcp-sequential-ip
cache-size=10000
dns-forward-max=600
edns-packet-max=1232
domain=lan
local=/lan/
server=1.1.1.1
server=8.8.8.8
server=208.67.222.222
server=208.67.220.220
server=2606:4700:4700::1111
server=2606:4700:4700::1001
server=2620:119:35::35
server=2620:119:53::53
server=2001:4860:4860::8888
server=2001:4860:4860::8844
addn-hosts=/tmp/hosts
dhcp-leasefile=/tmp/dhcp.leases
resolv-file=/tmp/resolv.conf.d/resolv.conf.auto
stop-dns-rebind
rebind-localhost-ok
rebind-domain-ok=ihost.netflix.com
rebind-domain-ok=plex.tv
rebind-domain-ok=plex.direct
rebind-domain-ok=myharmony.com
rebind-domain-ok=phynd.net
conf-file=/usr/share/dnsmasq/trust-anchors.conf
dnssec
dnssec-no-timecheck
dhcp-broadcast=tag:needs-broadcast
conf-dir=/tmp/dnsmasq.d
user=dnsmasq
group=dnsmasq

dhcp-host=28:DF:EB:B6:9B:62,192.168.2.5,semiauto,8h
dhcp-host=DC:A6:32:C6:A7:27,192.168.2.6,raspi-bastion,8h
dhcp-host=C8:DB:26:04:7D:15,192.168.2.12,harmonyHub,4h
dhcp-host=48:D6:D5:92:C0:67,192.168.2.8,google-home-mini,8h
dhcp-host=94:6A:B0:81:79:44,192.168.2.130,LGwebOSTV,4h
dhcp-host=1C:D6:BE:38:2D:50,192.168.2.30,verizon-router,8h
dhcp-host=88:51:FB:EE:6A:D7,192.168.2.10,printer,8h
dhcp-host=34:97:F6:98:B3:C0,192.168.2.20,asus-ap-RT-AC1900P,8h
dhcp-host=00:E0:4C:36:03:F7,192.168.2.55,raspi0-rak-lora,4h
dhcp-host=78:5D:C8:A6:60:35,192.168.2.118,LGwebOSTV,4h
dhcp-host=,id:00:01:00:01:15:44:A2:45:10:78:D2:F1:26:EA,Elaine-PC,4h
dhcp-host=,id:00:01:00:01:25:1E:C3:4F:B8:27:EB:91:7E:7A,raspi-flasher
dhcp-host=,id:00:01:00:01:24:B7:ED:78:DC:A6:32:02:DD:48,raspi0-rak-lora
dhcp-host=,id:00:03:00:01:88:51:FB:EE:6A:D7,NPIEE6AD7
dhcp-host=,id:00:04:CD:B1:A1:FA:07:57:66:07:F5:52:81:41:90:EB:71:12,lightfoot
dhcp-host=,id:00:01:00:01:1D:85:35:9A:B8:AE:ED:D3:BB:10,DESKTOP-10VQ0RQ
dhcp-host=A0:40:A0:8D:05:8D,192.168.2.133,VMB4000,4h
dhcp-host=,id:00:01:00:01:29:0F:EE:C1:DC:A6:32:C6:A7:27,raspi4-bastion
dhcp-host=,id:00:01:00:01:29:D9:64:3D:28:DF:EB:B6:9B:62,semiauto
dhcp-host=28:29:86:65:02:7B,192.168.2.62,apc65027B,4h
dhcp-host=D8:28:C9:B9:2F:97,192.168.2.68,GEMODULE5418,4h
dhcp-host=BC:CF:4F:E0:83:FE,192.168.2.58,XS1930,4h
dhcp-host=00:90:FB:77:21:EE,192.168.2.52,bobber-gateway,2h
dhcp-host=B4:B0:24:B4:4C:69,192.168.2.53,KP405,4h
dhcp-host=28:87:BA:63:3F:AE,192.168.2.70,KD110,4h
dhcp-host=64:52:99:81:4D:CA,192.168.2.134,MyQ-2DD,4h
dhcp-host=D8:EC:E5:7F:AC:DD,192.168.2.40,XS1930-12HP,2h
dhcp-host=B8:27:EB:C4:2B:2F,192.168.2.45,raspi-flasher,6h
dhcp-host=8C:49:62:5C:23:B5,192.168.2.48,RokuUltra-Projector,4h
dhcp-host=60:81:F9:81:F4:B7,192.168.2.46,Helium-Hotspot,12h
dhcp-host=00:1B:4D:02:85:37,192.168.2.11,raidmachine,4h
dhcp-host=B4:B0:24:EA:EC:68,192.168.2.60,kasa-outlet-dadslight,2h
dhcp-host=1C:61:B4:16:13:7A,192.168.2.49,KP303
dhcp-host=A4:BF:01:26:D7:0C,192.168.2.66,z2,4h
dhcp-host=,id:00:02:00:00:AB:11:D0:25:FB:DF:AE:A7:47:12,GRIP-B82CA0E9C0C3
dhcp-host=14:7D:DA:3E:CC:AA,192.168.2.56,blade
dhcp-host=6C:0B:84:EE:EE:95,192.168.2.69,poseidon
dhcp-host=6C:0B:84:EE:EE:96,192.168.2.85,poseidon-ilo
dhcp-host=6C:0B:84:EE:EE:94,192.168.2.84
dhcp-host=00:25:90:CA:D2:CD,192.168.2.4,topgun,4h
dhcp-host=98:B7:85:00:F6:AB,192.168.2.3,4h
dhcp-host=98:B7:85:00:F6:AA,192.168.2.7,tgun10g1,12h
dhcp-host=6C:CD:D6:B9:FA:84,192.168.2.42,netgear5port-sw,8h
dhcp-host=00:25:90:CE:75:5C,192.168.2.83,supermicro-ilo,4h

dhcp-ignore-names=tag:dhcp_bogus_hostname
conf-file=/usr/share/dnsmasq/dhcpbogushostname.conf

bogus-priv
conf-file=/usr/share/dnsmasq/rfc6761.conf
dhcp-range=set:lan,192.168.2.40,192.168.2.254,255.255.255.0,8h
ra-param=br-lan,0,7200
dhcp-range=set:lan,::1000,::ffff,constructor:br-lan,slaac,ra-names,8h
dhcp-option=lan,option6:dns-server,[::]
enable-ra
quiet-ra
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