bcc-tcpsubnet - Man Page

Summarize and aggregate IPv4 TCP traffic by subnet.


tcpsubnet [-h] [-v] [--ebpf] [-J] [-f FORMAT] [-i INTERVAL] [subnets]


This tool summarizes and aggregates IPv4 TCP sent to the subnets passed in argument and prints to stdout on a fixed interval.

This uses dynamic tracing of kernel TCP send/receive functions, and will need to be updated to match kernel changes.

The traced data is summarized in-kernel using a BPF map to reduce overhead. At very high TCP event rates, the overhead may still be measurable. See the Overhead section for more details.

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


CONFIG_BPF and bcc.



Print USAGE message.


Run in verbose mode. Will output subnet evaluation and the BPF program


Format output in JSON.


Interval between updates, seconds (default 1).


Format output units. Supported values are bkmBKM. When using kmKM the output will be rounded to floor.


Prints the BPF program.


Comma separated list of subnets. Traffic will be categorized in theses subnets. Order matters. (default,,,,


Summarize TCP traffic by the default subnets:

# tcpsubnet

Summarize all TCP traffic:

# tcpsubnet

Summarize all TCP traffic and output in JSON and Kb:

# tcpsubnet -J -fk


(Standad output) Left hand side column:


(Standard output) Right hand side column:

Aggregate traffic in units passed as argument

(JSON output) date

Current date formatted in the system locale

(JSON output) time

Current time formatted in the system locale

(JSON output) entries

Map of subnets to aggregates. Values will be in format passed to -f


This traces all tcp_sendmsg function calls in the TCP/IP stack. It summarizes data in-kernel to reduce overhead. A simple iperf test (v2.0.5) with the default values shows a loss of ~5% throughput. On 10 runs without tcpsubnet running the average throughput was 32.42Gb/s, with tcpsubnet enabled it was 31.26Gb/s. This is not meant to be used as a long running service. Use it for troubleshooting or for a controlled interval. As always, try it out in a test environment first.


This is from bcc.


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




Unstable - in development.


Rodrigo Manyari


tcptop(8) by Brendan Gregg

See Also



2018-03-01 USER COMMANDS