[Kea-users] Struggling with "failed to select a subnet for incoming packet" - Kea 3.0.3
Tim Harman
tim at muppetz.com
Thu Apr 9 20:15:44 UTC 2026
On 10/04/2026 5:10 am, Doug Freed wrote:
> On 4/9/26 03:39, Darren Ankney wrote:
>> Hi Tim,
>>
>> Could you attach the pcap of the client traffic? Nothing is jumping
>> out from the included log messages. It would be ideal if the pcap
>> included both unsuccessful renewal and successful DORA exchanges.
>>
>> Thank you,
>> Darren Ankney
>
> It would also be good to crank the logging up to DEBUG level 99 during
> the pcap. There's a lot of useful debug logging around subnet
> selection that would likely provide insight here.
>
> -Doug
A small snippet.
tcpdump capture and full log outputs are attached.
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.703 DEBUG
[kea-dhcp4.packets/297513.140641718414336] DHCP4_BUFFER_RECEIVED
received buffer from 192.168.0.174:68 to 192.168.0.1:67 over interface
eth1
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.704 DEBUG
[kea-dhcp4.options/297513.140641684354752] DHCP4_BUFFER_UNPACK parsing
buffer received from 192.168.0.174 to 192.168.0.1 over interface eth1
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.704 INFO
[kea-dhcp4.dhcp4/297513.140641684354752] DHCP4_QUERY_LABEL received
query: [hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0x8c6f352f
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 INFO
[kea-dhcp4.packets/297513.140641684354752] DHCP4_PACKET_RECEIVED
[hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0x8c6f352f: DHCPREQUEST (type 3) received from 192.168.0.174 to
192.168.0.1 on interface eth1
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.packets/297513.140641684354752] DHCP4_QUERY_DATA [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f, packet
details: local_address=192.168.0.1:67, remote_address=192.168.0.174:68,
Apr 10 08:01:36 kea-dhcp4[297513]: msg_type=DHCPREQUEST (3),
trans_id=0x8c6f352f,
Apr 10 08:01:36 kea-dhcp4[297513]: options:
Apr 10 08:01:36 kea-dhcp4[297513]: type=053, len=001: 3 (uint8)
Apr 10 08:01:36 kea-dhcp4[297513]: type=055, len=012: 1(uint8)
3(uint8) 6(uint8) 15(uint8) 26(uint8) 28(uint8) 51(uint8) 58(uint8)
59(uint8) 43(uint8) 114(uint8) 108(uint8)
Apr 10 08:01:36 kea-dhcp4[297513]: type=057, len=002: 1500 (uint16)
Apr 10 08:01:36 kea-dhcp4[297513]: type=060, len=015:
"android-dhcp-11" (string)
Apr 10 08:01:36 kea-dhcp4[297513]: type=061, len=007:
01:6c:f7:34:ef:8f:f1
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641684354752]
DHCPSRV_SUBNET4_SELECT_NO_RAI_OPTIONS No RAI options found to use for
subnet selection.
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641684354752]
DHCPSRV_SUBNET4_SELECT_NO_RELAY_ADDRESS Relay address (giaddr) in client
packet is empty.
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641684354752]
DHCPSRV_SUBNET4_SELECT_NO_USABLE_ADDRESS No subnet selected because no
suitable address to use for subnet selection was found.
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.packets/297513.140641684354752] DHCP4_SUBNET_SELECTION_FAILED
[hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0x8c6f352f: failed to select subnet for the client
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.dhcp4/297513.140641684354752] DHCP4_CLASS_ASSIGNED [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f: client
packet has been assigned to the following class: UNKNOWN
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.dhcp4/297513.140641684354752]
DHCP4_CLASSES_ASSIGNED_AFTER_SUBNET_SELECTION [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f: client
packet has been assigned to the following classes: ALL,
VENDOR_CLASS_android-dhcp-11, UNKNOWN
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.leases/297513.140641684354752] DHCP4_REQUEST [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f: server
is processing DHCPREQUEST with hint=192.168.0.174
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 ERROR
[kea-dhcp4.bad-packets/297513.140641684354752] DHCP4_PACKET_NAK_0001
[hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0x8c6f352f: failed to select a subnet for incoming packet, src
192.168.0.174, type DHCPREQUEST
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.705 DEBUG
[kea-dhcp4.callouts/297513.140641684354752] HOOKS_CALLOUTS_BEGIN begin
all callouts for hook leases4_committed
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.706 DEBUG
[kea-dhcp4.callouts/297513.140641684354752] HOOKS_CALLOUT_CALLED hooks
library with index 1 has called a callout on hook leases4_committed that
has address 0x7fe9b1a7e860 (callout duration: 0.058 ms)
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.706 DEBUG
[kea-dhcp4.callouts/297513.140641684354752] HOOKS_CALLOUTS_COMPLETE
completed callouts for hook leases4_committed (total callouts duration:
0.058 ms)
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.706 DEBUG
[kea-dhcp4.options/297513.140641684354752] DHCP4_PACKET_PACK [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f:
preparing on-wire format of the packet to be sent
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.706 INFO
[kea-dhcp4.packets/297513.140641684354752] DHCP4_PACKET_SEND [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f: trying
to send packet DHCPNAK (type 6) from 192.168.0.1:67 to 192.168.0.174:68
on interface eth1
Apr 10 08:01:36 kea-dhcp4[297513]: 2026-04-10 08:01:36.706 DEBUG
[kea-dhcp4.packets/297513.140641684354752] DHCP4_RESPONSE_DATA [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0x8c6f352f:
responding with packet DHCPNAK (type 6), packet details:
local_address=192.168.0.1:67, remote_address=192.168.0.174:68,
Apr 10 08:01:36 kea-dhcp4[297513]: msg_type=DHCPNAK (6),
trans_id=0x8c6f352f,
Apr 10 08:01:36 kea-dhcp4[297513]: options:
Apr 10 08:01:36 kea-dhcp4[297513]: type=053, len=001: 6 (uint8)
Apr 10 08:01:36 kea-dhcp4[297513]: type=054, len=004: 192.168.0.1
(ipv4-address)
Apr 10 08:01:36 kea-dhcp4[297513]: type=061, len=007:
01:6c:f7:34:ef:8f:f1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.901 DEBUG
[kea-dhcp4.packets/297513.140641718414336] DHCP4_BUFFER_RECEIVED
received buffer from 0.0.0.0:68 to 255.255.255.255:67 over interface
eth1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.options/297513.140641675962048] DHCP4_BUFFER_UNPACK parsing
buffer received from 0.0.0.0 to 255.255.255.255 over interface eth1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 INFO
[kea-dhcp4.dhcp4/297513.140641675962048] DHCP4_QUERY_LABEL received
query: [hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0xe07f740b
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048]
DHCPSRV_SUBNET4_SELECT_NO_RAI_OPTIONS No RAI options found to use for
subnet selection.
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048]
DHCPSRV_SUBNET4_SELECT_NO_RELAY_ADDRESS Relay address (giaddr) in client
packet is empty.
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048]
DHCPSRV_SUBNET4_SELECT_BY_INTERFACE_NO_MATCH No subnet matches
interface: eth1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048] DHCPSRV_CFGMGR_SUBNET4_ADDR
selected subnet 192.168.0.0/24 for packet received by matching address
192.168.0.1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.packets/297513.140641675962048] DHCP4_SUBNET_SELECTED
[hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0xe07f740b: the subnet with ID 1 was selected for client assignments
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.packets/297513.140641675962048] DHCP4_SUBNET_DATA [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0xe07f740b: the
selected subnet details: 192.168.0.0/24
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 INFO
[kea-dhcp4.packets/297513.140641675962048] DHCP4_PACKET_RECEIVED
[hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0xe07f740b: DHCPDISCOVER (type 1) received from 0.0.0.0 to
255.255.255.255 on interface eth1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.packets/297513.140641675962048] DHCP4_QUERY_DATA [hwtype=1
6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1], tid=0xe07f740b, packet
details: local_address=255.255.255.255:67, remote_address=0.0.0.0:68,
Apr 10 08:01:38 kea-dhcp4[297513]: msg_type=DHCPDISCOVER (1),
trans_id=0xe07f740b,
Apr 10 08:01:38 kea-dhcp4[297513]: options:
Apr 10 08:01:38 kea-dhcp4[297513]: type=053, len=001: 1 (uint8)
Apr 10 08:01:38 kea-dhcp4[297513]: type=055, len=012: 1(uint8)
3(uint8) 6(uint8) 15(uint8) 26(uint8) 28(uint8) 51(uint8) 58(uint8)
59(uint8) 43(uint8) 114(uint8) 108(uint8)
Apr 10 08:01:38 kea-dhcp4[297513]: type=057, len=002: 1500 (uint16)
Apr 10 08:01:38 kea-dhcp4[297513]: type=060, len=015:
"android-dhcp-11" (string)
Apr 10 08:01:38 kea-dhcp4[297513]: type=061, len=007:
01:6c:f7:34:ef:8f:f1
Apr 10 08:01:38 kea-dhcp4[297513]: type=080, len=000: ''
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.902 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048]
DHCPSRV_SUBNET4_SELECT_NO_RAI_OPTIONS No RAI options found to use for
subnet selection.
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.903 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048]
DHCPSRV_SUBNET4_SELECT_NO_RELAY_ADDRESS Relay address (giaddr) in client
packet is empty.
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.903 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048]
DHCPSRV_SUBNET4_SELECT_BY_INTERFACE_NO_MATCH No subnet matches
interface: eth1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.903 DEBUG
[kea-dhcp4.dhcpsrv/297513.140641675962048] DHCPSRV_CFGMGR_SUBNET4_ADDR
selected subnet 192.168.0.0/24 for packet received by matching address
192.168.0.1
Apr 10 08:01:38 kea-dhcp4[297513]: 2026-04-10 08:01:38.903 DEBUG
[kea-dhcp4.packets/297513.140641675962048] DHCP4_SUBNET_SELECTED
[hwtype=1 6c:f7:34:ef:8f:f1], cid=[01:6c:f7:34:ef:8f:f1],
tid=0xe07f740b: the subnet with ID 1 was selected for client assignments
Kind Regards,
Tim Harman
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dhcp-debug-level-99.pcap
Type: application/vnd.tcpdump.pcap
Size: 24565 bytes
Desc: not available
URL: <https://lists.isc.org/pipermail/kea-users/attachments/20260410/c712cb03/attachment-0001.pcap>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dhcp-during-pcap.logs.gz
Type: application/x-gzip
Size: 45328 bytes
Desc: not available
URL: <https://lists.isc.org/pipermail/kea-users/attachments/20260410/c712cb03/attachment-0001.bin>
More information about the Kea-users
mailing list