Bug 136618

Summary: Ethereal reports wrong checksum on outgoing UDP packets
Product: [Fedora] Fedora Reporter: Tomas Mraz <tmraz>
Component: tcpdumpAssignee: Harald Hoyer <harald>
Status: CLOSED DUPLICATE QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: rawhideCC: rvokal
Target Milestone: ---   
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Hardware: i386   
OS: Linux   
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Fixed In Version: Doc Type: Bug Fix
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Last Closed: 2006-02-21 19:06:31 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Flags
A very simple program to send UDP packets none

Description Tomas Mraz 2004-10-21 08:25:16 UTC 
Description of problem:
When Ethereal captures outgoing UDP packets it reports a wrong
checksum on them however when I use it to capture the packets on the
receiving side the checksum is OK.

Version-Release number of selected component (if applicable):
0.10.5 from current devel

How reproducible:
Run a program which sends out UDP packets and capture them using Ethereal.

Steps to Reproduce:
1.
2.
3.
  
Actual results:
The captured packets have incorrect checksum but in fact they haven't
as verified on receiving side.

Expected results:
The captured packets have correct checksum.

Additional info:
tcpdump seems to capture the packets with right checksum.
Comment 1 Tomas Mraz 2004-10-21 08:38:12 UTC 
Sorry for the last info: tcpdump actually captures the packets with
WRONG checksums too. So the problem lies probably in libpcap?
Comment 2 Tomas Mraz 2004-10-21 08:39:30 UTC 
Created attachment 105578 [details]
A very simple program to send UDP packets

Change IP address to host you want to send the packets to.
Comment 3 Harald Hoyer 2004-10-21 08:44:01 UTC 
which NIC?
Comment 4 Tomas Mraz 2004-10-21 08:50:33 UTC 
02:0c.0 Ethernet controller: Intel Corp. 82540EM Gigabit Ethernet
Controller (rev 02)
        Subsystem: Dell Computer Corporation: Unknown device 0151
        Flags: bus master, 66Mhz, medium devsel, latency 64, IRQ 9
        Memory at fcfe0000 (32-bit, non-prefetchable)
        I/O ports at df40 [size=64]
        Capabilities: [dc] Power Management version 2
        Capabilities: [e4] PCI-X non-bridge device.
        Capabilities: [f0] Message Signalled Interrupts: 64bit+
Queue=0/0 Enable-

libpcap version 0.8.3, kernel 2.6.8-1.610
Comment 5 Harald Hoyer 2004-10-21 08:53:22 UTC 
some network cards compute the checksum on their own..
maybe a dup of bug #129823
Comment 6 Harald Hoyer 2004-10-21 08:54:37 UTC 
Oh, same NIC... 

*** This bug has been marked as a duplicate of 129823 ***
Comment 7 Radek Vokál 2004-10-22 07:30:38 UTC 
This is described by ethereal developers -
http://www.ethereal.com/faq#q5.14
Comment 8 Red Hat Bugzilla 2006-02-21 19:06:31 UTC 
Changed to 'CLOSED' state since 'RESOLVED' has been deprecated.