[Bugme-new] [Bug 16601] New: Multicast MAC when sending via gateway

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Mon Aug 16 01:06:18 PDT 2010


https://bugzilla.kernel.org/show_bug.cgi?id=16601

           Summary: Multicast MAC when sending via gateway
           Product: Networking
           Version: 2.5
    Kernel Version: 2.6.26
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: IPV4
        AssignedTo: shemminger at linux-foundation.org
        ReportedBy: Nikita.Rastegaev at oktetlabs.ru
                CC: Alexandra.Kossovsky at oktetlabs.ru
        Regression: No


Created an attachment (id=27461)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=27461)
Configuration and simple test for the issue

I observe some strange behavior when sending multicast datagrams via gateway.
It appears that destination MAC in UDP packets differs when using connected and
connectionless socket. In case of connectionless socket destination MAC field
of
UDP header is filled with MAC address of gateway, but in case we use connect()
with multicast address, destination MAC is set to multicast MAC. I don't know,
which behavior is right, but different behavior is unexpected.

I run the attached test on thorin1 machine and use thorin2 as a gateway.
thorin1 is running 2.6.26-2-686 kernel, thorin2 is 2.6.26-2-amd64.
I also attach ifconfig and route output for this machines and tcpdump output
on thorin2 when running test. There we can see the following:

16:02:30.567909 00:27:0e:09:01:2a > 00:27:0e:09:02:2a, ethertype IPv4 (0x0800),
length 58: 10.54.10.1.40074 > 237.92.130.210.51721: UDP, length 16
16:02:30.567984 00:27:0e:09:01:2a > 01:00:5e:5c:82:d2, ethertype IPv4 (0x0800),
length 74: 10.54.10.1.43360 > 237.92.130.210.51721: UDP, length 32

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