ifconfig之下，dropped包的含义。

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Linux网络排查：ifconfig中errors、dropped、overruns、frame字段详解与实战 Linux网络接口统计计数器是判断网络健康状况的重要依据，其中errors、dropped、overruns、frame等字段分别对应物理层、驱动层和内核协议栈的不同问题。理解这些计数器的统计原理，能帮助运维人员从一串数字中快速定位丢包根因，避免盲目重启网卡。在实际故障排查中，结合ethtool细分计数、dmesg驱动日志和ip命令对应关系，可以系统性地判断是网线质量、缓冲区溢出还是双工不匹配。通过监控/sys/class/net/eth0/statistics/下的文件，还能将这些关键指标接入Promet 阅读详情

ifconfig shows dropped rx packets

This document (7007165) is provided subject to the disclaimer at the end of this document.
Environment
SUSE Linux Enterprise Server 11 Service Pack 2
Situation
ifconfig shows dropped rx packets
After updating to SLES 11 SP2 packets are being dropped
Dropped counter incrementing
rx_dropped counter is incrementing

Customers have reported seeing dropped packets when examining statistics on their network card, bonds, or virtual interfaces.

Resolution
Working as designed.
Cause
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
Bad / Unintended VLAN tags
Unknown / Unregistered protocols

If any frames meet those conditions, they are dropped before the protocol stack and the rx_dropped counter is incremented.
Additional Information
Care should be taken to confirm that frames are not being legitimately dropped. A quick way to test this (WARNING: this test does not work for bonding interfaces) is to start a packet capture:

host:~# tcpdump

And then watching the rx_dropped counter. If it stops incrementing while the tcpdump is running; then it is more than likely showing drops because of the reasons listed earlier. If frames continue to be dropped while running tcpdump, investigation should take place to determine root cause.

This effect is seen starting from SLES 11 SP2, as it utilizes a 3.x kernel series. Previous SLES versions do not exhibit it (that are using kernels prior to 2.6.37)

Additional information can be found by researching commit # caf586e5
Disclaimer

This Support Knowledgebase provides a valuable tool for NetIQ/Novell/SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

    Document ID:7007165
    Creation Date:17-MAY-12
    Modified Date:21-JUN-13
        SUSESUSE Linux Enterprise Server

http://www.novell.com/support/kb/doc.php?id=7007165

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