tcpdump check sum errors.

[Sherwood Botsford]

I'm running mail services (exim, fetchmail, popper) on FreeBSD 4.5

In a session trying to track down a problem related to a bad 
cable, I found that 
tcpdump -i xl0 -v -v -v host pop.incentre.net 

has lots of lines like this:

20:20:11.166767 postie.sjsa.internal.net.1126 > 
bach.ccinet.ab.ca.pop3: F [bad tcp cksum 4f5e!] 
61:61(0) ack 2075 win 33304 <nop,nop,timestamp 3005321 3937592> 
(DF) (ttl 64, id 57145, len 52, bad cksum 0!)

But netstat -I xl0 -w 10 during the same interval when the 
above were coming down at 5-10 per second showed:

            input          (xl0)           output
   packets  errs      bytes    packets  errs      bytes colls
        32     0       4019         28     0       4573     0
        24     0       3512         22     0       4934     0
       444     0      30070        433     0     227132     0

Explanations? (I also get them on the local network;
it's not just this destination host.)

-- 
Sherwood Botsford
St. John's School of Alberta