this is a FAQ: http://www.susesecurity.com/faq/ : What does "kernel: martian source aabbccdd for 11223344, dev eth0" mean? -- These are packets that Linux does not expect from the direction they came from (i.e. packets from internal hosts coming in on the external interface). The cause is probably a misconfigured machine on your LAN. You can turn off logging those packets via /proc/sys/net/ipv4/conf/*interface*/log_martians which is documented in /usr/src/linux/Documentation/proc.txt