Bug 136618 - Ethereal reports wrong checksum on outgoing UDP packets
Ethereal reports wrong checksum on outgoing UDP packets
Status: CLOSED DUPLICATE of bug 129823
Product: Fedora
Classification: Fedora
Component: tcpdump (Show other bugs)
i386 Linux
medium Severity medium
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Assigned To: Harald Hoyer
Depends On:
  Show dependency treegraph
Reported: 2004-10-21 04:25 EDT by Tomas Mraz
Modified: 2007-11-30 17:10 EST (History)
1 user (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2006-02-21 14:06:31 EST
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RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
A very simple program to send UDP packets (761 bytes, text/plain)
2004-10-21 04:39 EDT, Tomas Mraz
no flags Details

  None (edit)
Description Tomas Mraz 2004-10-21 04:25:16 EDT
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:
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 04:38:12 EDT
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 04:39:30 EDT
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 04:44:01 EDT
which NIC?
Comment 4 Tomas Mraz 2004-10-21 04:50:33 EDT
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 04:53:22 EDT
some network cards compute the checksum on their own..
maybe a dup of bug #129823
Comment 6 Harald Hoyer 2004-10-21 04:54:37 EDT
Oh, same NIC... 

*** This bug has been marked as a duplicate of 129823 ***
Comment 7 Radek Vokal 2004-10-22 03:30:38 EDT
This is described by ethereal developers -
Comment 8 Red Hat Bugzilla 2006-02-21 14:06:31 EST
Changed to 'CLOSED' state since 'RESOLVED' has been deprecated.

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