Strange IP_MASQ Log..

[thegreencow () EV1 NET (thegreencow)]

While scanning my logs I noticed this a couple of days ago... I have posted
to comp.os.linux.security and performed various web searches (including a
deja search). So far no one has been able to answer these strange log
events.. perhaps someone here could shed some light onto the problem? I am
running Server as a gateway for my lan. All outside connections are
masqueraded through this on interface ppp0. Distro. is Redhat 6.0.

Feb 11 16:55:23 Server kernel: IP_MASQ:reverse ICMP: failed checksum from
216.68.133.113!
Feb 11 16:55:25 Server last message repeated 2 times
Feb 11 16:55:27 Server kernel: IP_MASQ:reverse ICMP: failed checksum from
216.68.120.129!
Feb 11 16:55:28 Server last message repeated 2 times
Feb 11 16:55:56 Server kernel: IP_MASQ:reverse ICMP: failed checksum from
216.68.133.113!
Feb 11 16:55:58 Server last message repeated 2 times
Feb 11 16:55:59 Server kernel: IP_MASQ:reverse ICMP: failed checksum from
216.68.120.129!
Feb 11 16:56:28 Server last message repeated 5 times

Thanks,
S.