Bug 186133

Summary: [patch] tcpdump(1): zero checksums are invalid for UDP over IPv6
Product: Base System Reporter: Christian Weisgerber <naddy>
Component: binAssignee: freebsd-bugs (Nobody) <bugs>
Status: Closed Overcome By Events    
Severity: Affects Only Me CC: thj
Priority: Normal    
Version: 10.0-PRERELEASE   
Hardware: Any   
OS: Any   
Attachments:
Description Flags
patch-print-udp.c
none
zerocksum.pcap none

Description Christian Weisgerber freebsd_committer freebsd_triage 2014-01-26 18:40:00 UTC 
As per RFC 2460, section 8.1, UDP packets over IPv6 *must* have a
non-zero checksum.  Currently tcpdump ignores this and will print
"udp sum ok".  Maybe the author didn't understand how the Internet
checksum works and thought the checksum calculation would catch
this.

This bug and the fix should be reported upstream, but that requires
registration and whatnot.

How-To-Repeat: 
$ tcpdump -nvr zerocksum.pcap

An example zerocksum.pcap file is attached.
Comment 1 Eitan Adler freebsd_committer freebsd_triage 2017-12-31 07:59:01 UTC 
For bugs matching the following criteria:

Status: In Progress Changed: (is less than) 2014-06-01

Reset to default assignee and clear in-progress tags.

Mail being skipped
Comment 2 Tom Jones freebsd_committer freebsd_triage 2020-07-11 14:23:54 UTC 
RFC 6935 allows 0 checksum for IPv6 in tunnel applications. If you still think this issue is relevant please create a bug with upstream, tcpdump no longer requires registration for changes.