What is this in my syslog and should I be concerned?

Solution 1:

Those are just DHCP messages, either your server, or another is looking to configure an interface.

Solution 2:

Your original question has been answered by NickW above, but in case it's helpful to you the next time something like this happens, here's a quick way to tell for yourself.

The last bit of that log line says "PROTO=UDP SPT=68 DPT=67".

This means that the packet denied by the firewall was a UDP packet, whose source port is 68, and whose destination is port 67.

You can then do: "egrep -w '67|68' /etc/services" in a terminal, and the output (at least on my Ubuntu box) shows:

bootps      67/tcp              # BOOTP server
bootps      67/udp
bootpc      68/tcp              # BOOTP client
bootpc      68/udp

You can google bootp/dhcp to learn more about the differences/similarities. Just wanted to show how you can take apart the iptables log line for yourself, for future reference.

The log line tells you other useful stuff, like the fact that the packet is coming "IN=eth0" or inbound on your eth0 interface.

PS: Question for you: what do you mean by "The private network that my server is in blocks bcast"?