[Kea-users] dhcp4 server stops responding to a device

[Rick Frey]

The listed Kea logs for DHCP_LEASE_ADVERT would indicate that Kea is sending an OFFER to the DISCOVER request.   It would seem unlikely that Kea logs the ADVERT without attempting to send the offer packet on the network (such a bug would likely affect more than your client).   You also mention that you had similar issue with the legacy ISC dhcpd server.   You also mention recent issue began after distro upgrade.  Assuming there were not changes to Kea with the upgrade.

Not enough info in thread to determine, but seems more probable that the OFFER is being dropped/blocked by your OS/network layer.  Generally, if offer packet is blocked by something such as NFTables/IPTables, Kea would also log something along the lines of "failed to send DHCPv4 packet: pkt4 send failed: sendmsg() returned with an error: Operation not permitted”.  Apparmor/SELinux or similar security controls could also be in play.

You may want to try packet capture without filters (or just limit to port 67/68) in case there are some breadcrumbs there.  If you have not already, recommend checking OS logs as well in case response packet dropped by your host.  You can also turn up Kea loglevel (severity DEBUG and increased debuglevel) but since Kea is logging ADVERT, not sure you’ll learn more there.  See https://kea.readthedocs.io/en/kea-2.4.1/arm/logging.html#logging-levels  



> On Jan 19, 2024, at 07:37, Gavin Davenport <gavdav at gavdav.net> wrote:
> 
> Does anyone have any idea why dhcp would not actually emit the dhcp response following logging
> 2024-01-19 13:35:02.390 INFO  [kea-dhcp4.leases/855.139674733151936] DHCP4_LEASE_ADVERT [hwtype=1 fc:fe:c2:05:3e:b7], cid=[no info], tid=0xf3db5a1f: lease 10.99.99.3 will be advertised
> 2024-01-19 13:35:17.539 INFO  [kea-dhcp4.leases/855.139674758330048] DHCP4_LEASE_ADVERT [hwtype=1 fc:fe:c2:05:3e:b7], cid=[no info], tid=0xf3db5a1f: lease 10.99.99.3 will be advertised
> 2024-01-19 13:35:32.689 INFO  [kea-dhcp4.leases/855.139674749937344] DHCP4_LEASE_ADVERT [hwtype=1 fc:fe:c2:05:3e:b7], cid=[no info], tid=0xf3db5a1f: lease 10.99.99.3 will be advertised
> 
> It's received the discover (visible in tcpdump) but why would it get jammed and refuse to respond to this ?
> 
> is there anything I have misconfigured in the scope ? Are there any improved debugging options I might use ?
> 
> -----Original Message-----
> From: Kea-users <kea-users-bounces at lists.isc.org> On Behalf Of Gavin Davenport
> Sent: 16 January 2024 20:46
> To: Kea user's list <kea-users at lists.isc.org>
> Subject: Re: [Kea-users] dhcp4 server stops responding to a device
> 
> I was using isc-dhcp and had this behaviour too:
> https://gitlab.isc.org/isc-projects/dhcp/-/issues/177
> 
> I switched to kea-dhcp4 and it fixed it.
> 
> I've since done a distro upgrade and it's gone flaky again. 
> 
> I've no idea how to diagnose signal quality from the data I can get from the wiser (there's a rest endpoint) but this isn't available when it gets unaddressed.

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