Recurring ICMP Bad Checksum Warning

Chuck Swiger cswiger at
Thu Jul 14 16:59:20 UTC 2011

On Jul 14, 2011, at 5:18 AM, monarci wrote:
> I am currently running a company's FreeBSD web server and I am constantly
> receiving the ICMP Bad Checksum warning.  

You most likely have a NIC with hardware checksum capabilities; tcpdump sees outgoing packets before the hardware generates the checksums.  You can double-check by sniffing the traffic from a laptop connected to a monitoring port of the switch, or put a hub in place for testing so that the laptop also receives the traffic.


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