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)