Using isc-dhcpd-4.3.3-P1 from FreeBSD ports, on an amd64 host
(Intel Xeon), running FreeBSD 10.3-BETA2.

The ethernet interface driver is igb, GbE NIC is
Intel PRO/1000 Network Connection version - 2.4.0.

The dhcpd server (in IPv4 mode) is running on a physical machine,
there is *no* virtualization involved, nor a jail or VIMAGE
a host firewall.


While it seems that most clients successfully communicate
with a dhcpd server, I can see a steady trickle of log
entries like:

Feb 19 14:26:06 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:06 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:07 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:08 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:08 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:14 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:14 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:14 dhcp2 dhcpd: 4 bad udp checksums in 5 packets
Feb 19 14:26:14 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:18 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:19 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:34 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 4 bad udp checksums in 7 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:36 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:39 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:40 dhcp2 dhcpd: 3 bad udp checksums in 5 packets
Feb 19 14:26:40 dhcp2 dhcpd: 3 bad udp checksums in 5 packets

Other services on this host have no problem with communication,
netstat -I igb0 does not show any I/O errors on the interface.

Note that this dhcpd server sees both the proxied as well as
link-local client requests.

Disabling checksum offloading on the NIC avoids the problem!
(ifconfig igb0 -rxcsum).

I can see that a recent release of isc-dhcpd-4.3 received
a bunch of workarounds for just this kind of a problem,
although these all concentrated on Linux or on virtualizes
network interfaces.

Seems the same problem still persists on a FreeBSD platform.


   Mark