linux - What are the reasons for UDP packets to be dropped by the network stack -


i see udp packets arriving on linux box (via tcpdump) destination port set 25555. however:

nc -l -u 25555

shows no traffic.

i've checked:

  1. iptables off
  2. destination mac address matches incoming interface
  3. destination ip address matches incoming interface
  4. ip checksum ok
  5. udp checksum ok

also, all packets being dropped, it's not problem overlowing rx buffers.

any ideas else may cause pakcets dropped?

you have process on machine reading datagrams arriving on port 25555. can see /proc/net/udp:

sl   local_address rem_address   st tx_queue rx_queue tr rexmits  tm->when uid timeout inode ref pointer   drops 104: 00000000:63d3 00000000:0000 07 00000000:00000000 00:00000000 00000000 0   0       1779298 2 fff810266fe0c 0

so process "stealing" datagrams want owned root (uid=0). , inode of socket 1779298, can search under /proc/pid/fd pids owned root. once figure out process listening there, you'll need decide whether terminate nc can listen instead.

unicast udp datagrams end going single process on linux system, if there multiple processes trying read same address.


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