Linux – Dropped packets in all Linux and Unix

ethernetlinuxlinux-networkingnetworkingvlan

I have a problem. I have a motherboard by Supermicro – X11SBA-LN4F. There are 4 ethernet ports. In the first port I connect to the internet. In the second port I connect to my local network.

When, I write ifconfig or netstat -i, I can see on my second interface (my local network) dropped packets. This count is incremented

em2       Link encap:Ethernet  HWaddr 0c:c4:7a:7b:91:3e
          inet addr:192.168.110.181  Bcast:192.168.110.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:17441 errors:0 dropped:1380 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1226317 (1.2 MB)  TX bytes:0 (0.0 B)

After my search from google, I found this:
https://www.novell.com/support/kb/doc.php?id=7007165

Beginning with kernel 2.6.37, it has been changed the meaning of dropped packet count. Before, dropped packets was most likely due to an error. Now, the rx_dropped counter shows statistics for dropped frames because of:

Softnet backlog full  -- (Measured from /proc/net/softnet_stat)
Bad / Unintended VLAN tags
Unknown / Unregistered protocols
IPv6 frames when the server is not configured for IPv6

If any frames meet those conditions, they are dropped before the protocol stack and the rx_dropped counter is incremented.

First of all, I have written this command:

tcpdump -vv -i em2

While this command is running, the count of dropped packets on my second interface is stopped. But, when I abort tcpdump, the count of dropped packets is incremented again.

  • I disabled IPv6
  • I checked all VLANS. On that port I have only one Untag VLAN in local network

  • I checked the file /proc/net/softnet_stat. In that file I have info from only first column and that is good

    00000013 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    00002fbc 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    000000f3 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    0000268f 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

  • I analyzed by "tcpdump" all traffic. I have only – ARP Request, Broadcats and Rip. And it is not bad

  • I enabled promiscuous mode, but that didn't help
  • I checked cables and connectors
  • I install the latest driver
  • I increased ring caches size, but that didn't help

  • And I checked all Unix and Linux: Zeroshell, Pfense, FreeBsd, Ubuntu Server (with native kernel & compiled by me), CentOS (with native kernel & compiled by me). All showed the same symptoms.

    ethtool -i em2

driver: igb
version: 5.3.4.4
firmware-version: 3.25, 0x800005d0
bus-info: 0000:06:00.0
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: no

All statistic on that interface:

ethtool -S em2

NIC statistics:
     rx_packets: 29675
     tx_packets: 0
     rx_bytes: 2208735
     tx_bytes: 0
     rx_broadcast: 29636
     tx_broadcast: 0
     rx_multicast: 39
     tx_multicast: 0
     multicast: 39
     collisions: 0
     rx_crc_errors: 0
     rx_no_buffer_count: 0
     rx_missed_errors: 0
     tx_aborted_errors: 0
     tx_carrier_errors: 0
     tx_window_errors: 0
     tx_abort_late_coll: 0
     tx_deferred_ok: 0
     tx_single_coll_ok: 0
     tx_multi_coll_ok: 0
     tx_timeout_count: 0
     rx_long_length_errors: 0
     rx_short_length_errors: 0
     rx_align_errors: 0
     tx_tcp_seg_good: 0
     tx_tcp_seg_failed: 0
     rx_flow_control_xon: 0
     rx_flow_control_xoff: 0
     tx_flow_control_xon: 0
     tx_flow_control_xoff: 0
     rx_long_byte_count: 2208735
     tx_dma_out_of_sync: 0
     lro_aggregated: 0
     lro_flushed: 0
     tx_smbus: 0
     rx_smbus: 0
     dropped_smbus: 0
     os2bmc_rx_by_bmc: 0
     os2bmc_tx_by_bmc: 0
     os2bmc_tx_by_host: 0
     os2bmc_rx_by_host: 0
     tx_hwtstamp_timeouts: 0
     rx_hwtstamp_cleared: 0
     rx_errors: 0
     tx_errors: 0
     tx_dropped: 0
     rx_length_errors: 0
     rx_over_errors: 0
     rx_frame_errors: 0
     rx_fifo_errors: 0
     tx_fifo_errors: 0
     tx_heartbeat_errors: 0
     tx_queue_0_packets: 0
     tx_queue_0_bytes: 0
     tx_queue_0_restart: 0
     rx_queue_0_packets: 29675
     rx_queue_0_bytes: 2090035
     rx_queue_0_drops: 0
     rx_queue_0_csum_err: 0
     rx_queue_0_alloc_failed: 0

Where is my problem? Please help me.

 ifconfig em2; ethtool -S em2


em2       Link encap:Ethernet  HWaddr 0c:c4:7a:7b:91:3e
          inet addr:192.168.110.181  Bcast:192.168.110.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:15387 errors:0 dropped:1224 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1085031 (1.0 MB)  TX bytes:0 (0.0 B)

NIC statistics:
     rx_packets: 15387
     tx_packets: 0
     rx_bytes: 1146579
     tx_bytes: 0
     rx_broadcast: 15367
     tx_broadcast: 0
     rx_multicast: 20
     tx_multicast: 0
     multicast: 20
     collisions: 0
     rx_crc_errors: 0
     rx_no_buffer_count: 0
     rx_missed_errors: 0
     tx_aborted_errors: 0
     tx_carrier_errors: 0
     tx_window_errors: 0
     tx_abort_late_coll: 0
     tx_deferred_ok: 0
     tx_single_coll_ok: 0
     tx_multi_coll_ok: 0
     tx_timeout_count: 0
     rx_long_length_errors: 0
     rx_short_length_errors: 0
     rx_align_errors: 0
     tx_tcp_seg_good: 0
     tx_tcp_seg_failed: 0
     rx_flow_control_xon: 0
     rx_flow_control_xoff: 0
     tx_flow_control_xon: 0
     tx_flow_control_xoff: 0
     rx_long_byte_count: 1146579
     tx_dma_out_of_sync: 0
     lro_aggregated: 0
     lro_flushed: 0
     tx_smbus: 0
     rx_smbus: 0
     dropped_smbus: 0
     os2bmc_rx_by_bmc: 0
     os2bmc_tx_by_bmc: 0
     os2bmc_tx_by_host: 0
     os2bmc_rx_by_host: 0
     tx_hwtstamp_timeouts: 0
     rx_hwtstamp_cleared: 0
     rx_errors: 0
     tx_errors: 0
     tx_dropped: 0
     rx_length_errors: 0
     rx_over_errors: 0
     rx_frame_errors: 0
     rx_fifo_errors: 0
     tx_fifo_errors: 0
     tx_heartbeat_errors: 0
     tx_queue_0_packets: 0
     tx_queue_0_bytes: 0
     tx_queue_0_restart: 0
     rx_queue_0_packets: 15387
     rx_queue_0_bytes: 1085031
     rx_queue_0_drops: 0
     rx_queue_0_csum_err: 0
     rx_queue_0_alloc_failed: 0

Best Answer

Probably what's happening is that you're seeing IPv6 broadcast traffic on your subnet, as per what you posted from a tcpdump output here:

12:19:41.622297 IP6 (hlim 1, next-header UDP (17) payload length: 112) fe80::a4a0:460b:c99a:c992.dhcpv6-client > ff02::1:2.dhcpv6-server: [udp sum ok] dhcp6 solicit (xid=455863 (elapsed-time 700) (client-ID hwaddr/time type 1 time 495735714 e03f49b54e07) (IA_NA IAID:65027913 T1:0 T2:0) (Client-FQDN) (vendor-class) (option-request vendor-specific-info DNS-server DNS-search-list Client-FQDN))

And as per what you wrote in your question here:

Beginning with kernel 2.6.37, it has been changed the meaning of dropped packet count. Before, dropped packets was most likely due to an error. Now, the rx_dropped counter shows statistics for dropped frames because of:

Softnet backlog full -- (Measured from /proc/net/softnet_stat)

Bad / Unintended VLAN tags

Unknown / Unregistered protocols

IPv6 frames when the server is not configured for IPv6

If any frames meet those conditions, they are dropped before the protocol stack and the rx_dropped counter is incremented.

From your output and your question, it would seem that you indeed have IPv6 disabled on the server.

This leads me to the conclusion that the dropped packets you're seeing is likely due to IPv6 broadcast traffic from other hosts on the network.

In order to test this, you can re-enable IPv6 and see if the dropped packets go away. If they do, this is harmless.

Related Topic