[Kea-users] NAK responses getting dropped

[Elton, Norman N]

Thanks all. Upgrading to 3.2.1 appears to have fixed this problem. The DHCPNAK packets are leaving the server with the broadcast bit properly set.

I stumbled on another mysql/tls issue that I’ll post in a new thread.

Norman



From: Kea-users <kea-users-bounces at lists.isc.org> on behalf of Sten Carlsen via Kea-users <kea-users at lists.isc.org>
Date: Tuesday, October 13, 2026 at 1:12 PM
To: Kea user's list <kea-users at lists.isc.org>
Cc: Sten Carlsen <stenc at s-carlsen.dk>
Subject: Re: [Kea-users] NAK responses getting dropped

Right, thanks. Just looked wrong to me.

--
Best regards
Sten Carlsen


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On 13 Oct 2026, at 18.24, Doug Freed via Kea-users <kea-users at lists.isc.org> wrote:

On 10/13/26 11:03, Sten Carlsen via Kea-users wrote:
On 13 Oct 2026, at 17.07, Elton, Norman N <wnelto at wm.edu> wrote:
The same packet captured in tcpdump (running on the server - in the docker container):

IP (tos 0x0, ttl 64, id 19991, offset 0, flags [DF], proto UDP (17), length 278)
    172.21.0.2.67 > 100.70.0.1.67: [bad udp cksum 0x1172 -> 0xd2df!] BOOTP/DHCP, Reply, length 250, hops 1, xid 0x12345678, Flags [none] (0x0000)
Did you notice the "bad udp cksum …"?
This is normal.  NICs generally support checksum offloading, so the kernel does not set the checksum field to its correct value before handing off the packet to the NIC for sending, and this is reflected in tcpdump.  It's only a problem if it's on an inbound packet, or you know checksum offloading is turned off.

-Doug
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