I have a Fedora 20 machine which is receiving UDP broadcast packets at
regular intervals on a high port. I have a program which is trying to
receive these packets and failing to do so. As part of the bug
investigation, I checked to see of Ncat would receive them. It also doesn't.
If I run, "tcpdump -i eth2 port 29531", I see each of the packets
arriving just as I expect. But if I then run, "nc -lu 29531" or my
program, I don't see anything!
On this machine, a Dell R510, eth0 and eth1 are motherboard ports with
the bnx2 driver. eth2 through eth9 are provided by two 4-port Intel PCI
cards with 82576 chips using the igb driver. The packets arrive on the
Intel ports, eth2 through eth9. SELinux and the firewall are disabled on
the machine.
If I move the cable to eth0, my application and Ncat see the packets. Of
course, this solves nothing since I need it to work on the eight add-in
ports. But comparing the output of "ethtool -k" on eth0 and eth2, I
observe a few differences:
feature eth0 eth2
tx-checksum-sctp off [fixed] on
tx-tcp-ecn-segmentation on off [fixed]
rx-vlan-filter off [fixed] on [fixed]
rx-all off [fixed] on
I set rx-all on for eth2 because I also receive some packets with an
invalid length field and need them to get through. The only other
difference that seems like it might apply to a received packet is
rx-vlan-filter but ethtool won't allow me to disable that feature. If
this feature is relevant to the problem, how can I disable it?
Attached is a short pcap file containing a few of the packets which
don't make it to an application program.
--
Dave Close
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