[Kea-users] Struggling with "failed to select a subnet for incoming packet" - Kea 3.0.3
Tim Harman
tim at muppetz.com
Wed Apr 8 20:04:39 UTC 2026
Hi,
I am a VyOS user and have recently moved from VyOS 1.4.4 to VyOS 1.5.0.
This means a migration from ISC DHCP to Kea DHCP.
And since moving to Kea, I've been struggling with DHCP renewals not
working properly. It seems that no Unicast DHCP renewal requests work,
the are always NAK'd as follows:
Apr 09 01:18:09 kea-dhcp4[208553]: 2026-04-09 01:18:09.326 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 6c:79:b8:ec:13:49], cid=[no info], tid=0x9eb95cf4: failed to
select a subnet for incoming packet, src 192.168.0.152, type DHCPREQUEST
Apr 09 01:26:03 kea-dhcp4[208553]: 2026-04-09 01:26:03.573 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 50:32:37:c4:fa:8c], cid=[01:50:32:37:c4:fa:8c],
tid=0xd53ecc4e: failed to select a subnet for incoming packet, src
192.168.0.101, type DHCPREQUEST
Apr 09 01:37:53 kea-dhcp4[208553]: 2026-04-09 01:37:52.998 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 bc:35:1e:26:53:38], cid=[no info], tid=0x60c4b446: failed to
select a subnet for incoming packet, src 192.168.0.182, type DHCPREQUEST
Apr 09 01:46:25 kea-dhcp4[208553]: 2026-04-09 01:46:25.880 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 70:a7:41:c1:4b:fa], cid=[no info], tid=0x225f7ce0: failed to
select a subnet for incoming packet, src 192.168.0.4, type DHCPREQUEST
Apr 09 01:46:39 kea-dhcp4[208553]: 2026-04-09 01:46:39.880 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 78:11:dc:70:b9:4d], cid=[01:78:11:dc:70:b9:4d],
tid=0xe072c478: failed to select a subnet for incoming packet, src
192.168.0.11, type DHCPREQUEST
Apr 09 02:01:21 kea-dhcp4[208553]: 2026-04-09 02:01:21.951 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 54:60:09:e0:e3:40], cid=[no info], tid=0x12690ba5: failed to
select a subnet for incoming packet, src 192.168.0.115, type DHCPREQUEST
Apr 09 02:01:24 kea-dhcp4[208553]: 2026-04-09 02:01:24.981 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 54:60:09:e0:e3:40], cid=[no info], tid=0x12690ba5: failed to
select a subnet for incoming packet, src 192.168.0.115, type DHCPREQUEST
Apr 09 03:02:13 kea-dhcp4[208553]: 2026-04-09 03:02:13.422 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 0c:b2:b7:5c:ad:84], cid=[no info], tid=0x16ae3e33: failed to
select a subnet for incoming packet, src 192.168.0.150, type DHCPREQUEST
Apr 09 03:12:04 kea-dhcp4[208553]: 2026-04-09 03:12:04.168 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 f0:2f:4b:39:11:ee], cid=[01:f0:2f:4b:39:11:ee],
tid=0x11d6a0ef: failed to select a subnet for incoming packet, src
192.168.0.188, type DHCPREQUEST
Apr 09 03:16:00 kea-dhcp4[208553]: 2026-04-09 03:16:00.884 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 54:e0:19:67:41:80], cid=[no info], tid=0xc84563d9: failed to
select a subnet for incoming packet, src 192.168.0.29, type DHCPREQUEST
Apr 09 03:32:18 kea-dhcp4[208553]: 2026-04-09 03:32:18.740 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 a0:c9:a0:08:93:3e], cid=[01:a0:c9:a0:08:93:3e],
tid=0x621e3b6e: failed to select a subnet for incoming packet, src
192.168.0.16, type DHCPREQUEST
Apr 09 03:48:17 kea-dhcp4[208553]: 2026-04-09 03:48:17.413 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 24:6f:28:1b:5d:c8], cid=[01:24:6f:28:1b:5d:c8],
tid=0x2c0cc177: failed to select a subnet for incoming packet, src
192.168.0.166, type DHCPREQUEST
Apr 09 05:10:15 kea-dhcp4[208553]: 2026-04-09 05:10:15.312 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 f0:5c:77:bc:ac:51], cid=[01:f0:5c:77:bc:ac:51],
tid=0x18582fd0: failed to select a subnet for incoming packet, src
192.168.0.153, type DHCPREQUEST
Apr 09 05:27:07 kea-dhcp4[208553]: 2026-04-09 05:27:07.214 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 02:77:0f:6d:f3:b9], cid=[01:02:77:0f:6d:f3:b9],
tid=0x36b8208c: failed to select a subnet for incoming packet, src
192.168.0.186, type DHCPREQUEST
Apr 09 05:33:12 kea-dhcp4[208553]: 2026-04-09 05:33:12.914 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 c6:df:8f:ca:f9:27], cid=[01:c6:df:8f:ca:f9:27], tid=0x915835c:
failed to select a subnet for incoming packet, src 192.168.0.197, type
DHCPREQUEST
Apr 09 05:42:49 kea-dhcp4[208553]: 2026-04-09 05:42:49.412 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 a8:ca:77:8b:60:48],
cid=[ff:77:8b:60:48:00:01:00:01:2d:3a:e0:bd:a8:ca:77:8b:60:48],
tid=0x7c422899: failed to select a subnet for incoming packet, src
192.168.0.185, type DHCPREQUEST
Apr 09 05:45:43 kea-dhcp4[208553]: 2026-04-09 05:45:43.088 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 5e:55:58:1c:8f:d0], cid=[01:5e:55:58:1c:8f:d0],
tid=0xa60ac243: failed to select a subnet for incoming packet, src
192.168.0.187, type DHCPREQUEST
Apr 09 06:04:22 kea-dhcp4[208553]: 2026-04-09 06:04:22.812 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 84:0d:8e:63:de:8e], cid=[no info], tid=0xb55fe8da: failed to
select a subnet for incoming packet, src 192.168.0.70, type DHCPREQUEST
Apr 09 06:31:57 kea-dhcp4[208553]: 2026-04-09 06:31:57.110 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 d4:36:39:a9:ea:46], cid=[01:d4:36:39:a9:ea:46],
tid=0x78d4c7bd: failed to select a subnet for incoming packet, src
192.168.0.13, type DHCPREQUEST
Apr 09 07:01:42 kea-dhcp4[208553]: 2026-04-09 07:01:42.641 ERROR
[kea-dhcp4.bad-packets/208553.139835658786496] DHCP4_PACKET_NAK_0001
[hwtype=1 e4:2f:37:be:a0:17], cid=[01:e4:2f:37:be:a0:17],
tid=0x21fdeb8b: failed to select a subnet for incoming packet, src
192.168.0.157, type DHCPREQUEST
Apr 09 07:08:46 kea-dhcp4[208553]: 2026-04-09 07:08:46.920 ERROR
[kea-dhcp4.bad-packets/208553.139835650393792] DHCP4_PACKET_NAK_0001
[hwtype=1 9c:76:13:19:59:62], cid=[no info], tid=0x502959d8: failed to
select a subnet for incoming packet, src 192.168.0.175, type DHCPREQUEST
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.480 ERROR
[kea-dhcp4.bad-packets/231988.140669784841216] DHCP4_PACKET_NAK_0001
[hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0xf162a59f: failed to
select a subnet for incoming packet, src 192.168.0.183, type DHCPREQUEST
This makes the clients fall back to a standard broadcast DHCP Request,
which then works just fine:
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.480 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_RECEIVED
[hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0xf162a59f: DHCPREQUEST
(type 3) received from 192.168.0.183 to 192.168.0.1 on interface eth1
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.480 ERROR
[kea-dhcp4.bad-packets/231988.140669784841216] DHCP4_PACKET_NAK_0001
[hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0xf162a59f: failed to
select a subnet for incoming packet, src 192.168.0.183, type DHCPREQUEST
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.480 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_SEND [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0xf162a59f: trying to send packet
DHCPNAK (type 6) from 192.168.0.1:67 to 192.168.0.183:68 on interface
eth1
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.891 INFO
[kea-dhcp4.dhcp4/231988.140669784841216] DHCP4_QUERY_LABEL received
query: [hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0xe7001ba3
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.891 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_RECEIVED
[hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0xe7001ba3:
DHCPDISCOVER (type 1) received from 0.0.0.0 to 255.255.255.255 on
interface eth1
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.892 INFO
[kea-dhcp4.leases/231988.140669784841216] DHCP4_LEASE_OFFER [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0xe7001ba3: lease 192.168.0.183
will be offered
Apr 09 07:41:41 kea-dhcp4[231988]: 2026-04-09 07:41:41.892 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_SEND [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0xe7001ba3: trying to send packet
DHCPOFFER (type 2) from 192.168.0.1:67 to 192.168.0.183:68 on interface
eth1
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.459 INFO
[kea-dhcp4.dhcp4/231988.140669784841216] DHCP4_QUERY_LABEL received
query: [hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.459 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_RECEIVED
[hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75:
DHCPDISCOVER (type 1) received from 0.0.0.0 to 255.255.255.255 on
interface eth1
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.460 INFO
[kea-dhcp4.leases/231988.140669784841216] DHCP4_LEASE_OFFER [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75: lease 192.168.0.183
will be offered
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.460 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_SEND [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75: trying to send packet
DHCPOFFER (type 2) from 192.168.0.1:67 to 192.168.0.183:68 on interface
eth1
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.509 INFO
[kea-dhcp4.dhcp4/231988.140669784841216] DHCP4_QUERY_LABEL received
query: [hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.509 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_RECEIVED
[hwtype=1 78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75: DHCPREQUEST
(type 3) received from 0.0.0.0 to 255.255.255.255 on interface eth1
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.510 INFO
[kea-dhcp4.leases/231988.140669784841216] DHCP4_LEASE_ALLOC [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75: lease 192.168.0.183
has been allocated for 86400 seconds
Apr 09 07:42:00 kea-dhcp4[231988]: 2026-04-09 07:42:00.511 INFO
[kea-dhcp4.packets/231988.140669784841216] DHCP4_PACKET_SEND [hwtype=1
78:20:a5:62:a6:c8], cid=[no info], tid=0x13867c75: trying to send packet
DHCPACK (type 5) from 192.168.0.1:67 to 192.168.0.183:68 on interface
eth1
The device (router) doing DHCP is pretty simple, WAN interface (eth0)
and LAN interface (eth1)
tim at ferrari:~$ ip addr show eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc cake state UP
group default qlen 1000
link/ether 54:1e:56:66:66:66 brd ff:ff:ff:ff:ff:ff permaddr
de:dd:38:7c:da:e9
altname enp0s19
altname ens19
inet 192.168.0.1/24 brd 192.168.0.255 scope global eth1
valid_lft forever preferred_lft forever
inet6 2406:5a00:1ae0:9401::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::561e:56ff:fe66:6666/64 scope link
valid_lft forever preferred_lft forever
My configuration is as follows:
{
"Dhcp4": {
"interfaces-config": {
"interfaces": [ "eth1" ],
"dhcp-socket-type": "raw",
"service-sockets-max-retries": 60,
"service-sockets-retry-wait-time": 5000
},
"control-socket": {
"socket-type": "unix",
"socket-name": "/var/run/kea/dhcp4-ctrl-socket"
},
"lease-database": {
"type": "memfile",
"persist": true,
"name": "/config/dhcp/dhcp4-leases.csv"
},
"multi-threading": {
"enable-multi-threading": false
},
"option-def": [
{
"name": "wpad-url",
"code": 252,
"type": "string"
},
{
"name": "unifi-controller",
"code": 1,
"type": "ipv4-address",
"space": "ubnt"
}
],
"hooks-libraries": [
{
"library":
"/usr/lib/x86_64-linux-gnu/kea/hooks/libdhcp_lease_cmds.so",
"parameters": {}
}
],
"shared-networks": [
{
"name": "XXLAN",
"authoritative": true,
"subnet4": [
{
"subnet": "192.168.0.0/24",
"id": 1,
"interface": "eth1",
"user-context": {
"enable-ping-check": false
},
"option-data": [
{
"name": "domain-name-servers",
"data": "192.168.0.5"
},
{
"name": "domain-name",
"data": "X.com"
},
{
"name": "domain-search",
"data": "X.com"
},
{
"name": "ntp-servers",
"data": "192.168.0.1"
},
{
"name": "routers",
"data": "192.168.0.1"
}
],
"valid-lifetime": 86400,
"max-valid-lifetime": 86400,
"pools": [
{
"pool": "192.168.0.150 - 192.168.0.240"
}
],
"reservations": [
{
"hostname": "X",
"hw-address": "XX:76:6f:41:XX:XX",
"ip-address": "192.168.0.113"
},
{
"hostname": "XX",
"hw-address": "50:32:37:c4:XX:XX",
"ip-address": "192.168.0.101"
},
{
"hostname": "XX-tracker",
"hw-address": "24:0a:c4:58:XX:XX",
"ip-address": "192.168.0.72"
},
]
}
],
"user-context": {
"enable-ping-check": false
}
}
]
}
}
I do have a large number of reservations that I've not included, but the
same error occurs regardless of if the client is one with a static
reservation or not.
I have tried disabling threading (as you can see in the config, VyOS
generates config that enables it by default) but this hasn't helped
either.
I've got packet captures that show pretty clearly the packets are
normal, correct unicast packets, though happy to share my tcpdump if
that'd help.
Kea Details:
tim at ferrari:~$ /usr/sbin/kea-dhcp4 -V
3.0.3-git (3.0.3-git (vyos deb))
premium: no
linked with:
- log4cplus 2.0.8
- OpenSSL 3.0.18 30 Sep 2025
lease backends:
- Memfile backend 3.0
tim at ferrari:~$ /usr/sbin/kea-dhcp4 -t /var/run/kea/kea-dhcp4.conf
2026-04-09 07:59:04.531 INFO [kea-dhcp4.hooks/232752.140046183791616]
HOOKS_LIBRARY_CLOSED hooks library
/usr/lib/x86_64-linux-gnu/kea/hooks/libdhcp_lease_cmds.so successfully
closed
2026-04-09 07:59:04.531 INFO [kea-dhcp4.dhcpsrv/232752.140046183791616]
DHCPSRV_CFGMGR_NEW_SUBNET4 a new subnet has been added to configuration:
192.168.0.0/24 with params: valid-lifetime=86400
2026-04-09 07:59:04.533 INFO [kea-dhcp4.dhcpsrv/232752.140046183791616]
DHCPSRV_CFGMGR_SOCKET_TYPE_SELECT using socket type raw
2026-04-09 07:59:04.533 INFO [kea-dhcp4.dhcpsrv/232752.140046183791616]
DHCPSRV_CFGMGR_SOCKET_TYPE_SELECT using socket type raw
2026-04-09 07:59:04.533 INFO [kea-dhcp4.dhcpsrv/232752.140046183791616]
DHCPSRV_CFGMGR_ADD_IFACE listening on interface eth1
2026-04-09 07:59:04.533 INFO [kea-dhcp4.dhcpsrv/232752.140046183791616]
DHCPSRV_LEASE_MGR_BACKENDS_REGISTERED the following lease backend types
are available: memfile
2026-04-09 07:59:04.533 INFO [kea-dhcp4.hosts/232752.140046183791616]
HOSTS_BACKENDS_REGISTERED the following host backend types are
available:
2026-04-09 07:59:04.533 INFO [kea-dhcp4.dhcpsrv/232752.140046183791616]
DHCPSRV_FORENSIC_BACKENDS_REGISTERED the following forensic backend
types are available:
2026-04-09 07:59:04.533 INFO
[kea-dhcp4.database/232752.140046183791616] CONFIG_BACKENDS_REGISTERED
the following config backend types are available:
Happy to provide anymore details that might be relevant/helpful.
I'm _thinking_ I should log a bug as it seems to be that this should
work - all the debugging/reading I've done tells me this is a simple
config and it should have no problems, but something obviously is up.
Any help/suggestions/advice would be appreciated, thank you very much!
Tim
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