NAME

       tcpdrop - Trace kernel-based TCP packet drops with details. Uses Linux eBPF/bcc.

SYNOPSIS

       tcpdrop [-4 | -6] [-h]

DESCRIPTION

       This  tool  traces  TCP  packets  or  segments  that were dropped by the kernel, and shows
       details from the IP and TCP headers, the socket state, and the kernel stack trace. This is
       useful  for  debugging cases of high kernel drops, which can cause timer-based retransmits
       and performance issues.

       This tool works using dynamic tracing of the tcp_drop() kernel function, which requires  a
       recent kernel version.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -4     Trace IPv4 family only.

       -6     Trace IPv6 family only.

       -h     Print usage message.

EXAMPLES

       Trace kernel-based TCP packet drops with details:
              # tcpdrop

       Trace IPv4 family only:
              # tcpdrop -4

       Trace IPv6 family only:
              # tcpdrop -6

FIELDS

       TIME   Time of the drop, in HH:MM:SS format.

       PID    Process  ID  that  was  on-CPU during the drop. This may be unrelated, as drops can
              occur on the receive interrupt and be unrelated to the PID that was interrupted.

       IP     IP address family (4 or 6)

       SADDR  Source IP address.

       SPORT  Source TCP port.

       DADDR  Destination IP address.

       DPORT  Destionation TCP port.

       STATE  TCP session state ("ESTABLISHED", etc).

       FLAGS  TCP flags ("SYN", etc).

OVERHEAD

       This traces the kernel tcp_drop() function, which should be low frequency,  and  therefore
       the overhead of this tool should be negligible.

       As  always,  test  and  understand  this tools overhead for your types of workloads before
       production use.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also look in the bcc distribution for a companion _examples.txt  file  containing  example
       usage, output, and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       tcplife(8), tcpaccept(8), tcpconnect(8), tcptop(8)