tftp - bad checksum error? can't transfer file

Gary Gatten Ggatten at
Thu Jul 7 22:54:41 UTC 2011

>From my experience tcpdump is misleading re udp fragments and chksums.  If the packet gets fragmented, udp will report bad chksums at some point.

Check your file names (case), perms, etc.  90% of time I typo a name or forget to chmod the files; or when using tftp to write I forget to create a file with the correct name (and perms) first.

----- Original Message -----
From: Anton Shterenlikht [mailto:mexas at]
Sent: Thursday, July 07, 2011 05:44 PM
To: freebsd-questions at <freebsd-questions at>
Subject: tftp - bad checksum error? can't transfer file

I'm trying to troubleshoot tftpd(8).

% grep boot /etc/inetd.conf
tftp   dgram udp  wait root /usr/libexec/tftpd  tftpd -dd -l -s /tftpboot
tftp   dgram udp  wait root /usr/libexec/tftpd  tftpd -dd -l -s /tftpboot
bootps dgram udp  wait root /usr/libexec/bootpd bootpd -d4 -t0 /etc/bootptab

I'm trying to boot another node via bootp/tftp.

I'm monitoring what's going on with tcpdump -vv.

bootpd starts fine, and seems to read /etc/bootptab

But after that nothing happens, and after a few minutes
I get on the console of the host which I want to boot:

> bootp()/bsd.rd.IP32
Unable to execute bootp()/bsd.rd.IP32:  invalid argument

Does this tcpdump fragment help to understand where
the problem is: > buzi.tftp: [no cksum]  25 RRQ "/bsd.rd.IP32" octet (
23:25:21.024160 IP (tos 0x0, ttl 64, id 56, offset 0, flags [none], proto UDP (1
7), length 30, bad cksum 0 (->293a)!)
    buzi.19330 > [udp sum ok] UDP, length 2
23:25:51.013759 IP (tos 0x0, ttl 255, id 256, offset 0, flags [none], proto UDP
(17), length 53)

I'm happy to provide more detailed information
on the settings I use and a longer tcpdump output,
if this helps.

Many thanks

Anton Shterenlikht
Room 2.6, Queen's Building
Mech Eng Dept
Bristol University
University Walk, Bristol BS8 1TR, UK
Tel: +44 (0)117 331 5944
Fax: +44 (0)117 929 4423
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