[Kea-users] NAK responses getting dropped

[Doug Freed]

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