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Demonstrations of tcpsubnet, the Linux eBPF/bcc version.
tcpsubnet summarizes throughput by destination subnet.
It works only for IPv4. Eg:
# tcpsubnet
Tracing... Output every 1 secs. Hit Ctrl-C to end
[03/05/18 22:32:47] 8
[03/05/18 22:32:48]
[03/05/18 22:32:49]
[03/05/18 22:32:50]
[03/05/18 22:32:51]
[03/05/18 22:32:52] 10
[03/05/18 22:32:53]
This example output shows the number of bytes sent to (the
loopback interface). For demo purposes, I set netcat listening on port
8080, connected to it and sent the following payloads.
# nc 8080
The first line sends 7 digits plus the null character (8 bytes)
The second line sends 9 digits plus the null character (10 bytes)
Notice also, how tcpsubnet prints a header line with the current date
and time formatted in the current locale.
Try it yourself to get a feeling of how tcpsubnet works.
By default, tcpsubnet will categorize traffic in the following subnets:
The last subnet is a catch-all. In other words, anything that doesn't
match the first 4 defaults will be categorized under
You can change this default behavoir by passing a comma separated list
of subnets. Let's say we would like to know how much traffic we
are sending to We first find out what IPs resolves
to, Eg:
# dig +short
With this information, we can come up with a reasonable range of IPs
to monitor, Eg:
Tracing... Output every 1 secs. Hit Ctrl-C to end
[03/05/18 22:38:58] 5780 2205
[03/05/18 22:38:59] 2036 1183
[03/05/18 22:39:00]
[03/05/18 22:39:01] 12537
If we would like to be more accurate, we can use the two IPs returned
by dig, Eg:
# tcpsubnet,,
Tracing... Output every 1 secs. Hit Ctrl-C to end
[03/05/18 22:42:56] 1177 910
[03/05/18 22:42:57] 48704 892
[03/05/18 22:42:58] 891 858
[03/05/18 22:42:59] 11159 894
[03/05/18 22:43:00] 60601
NOTE: When used in production, it is expected that you will have full
information about your network topology. In which case you won't need
to approximate subnets nor need to put individual IP addresses like
we just did.
Notice that the order of the subnet matters. Say, we put as
the first element of the list and as the second, all the
traffic going to will have been categorized in as is contained in
The default ouput unit is bytes. You can change it by using the
-f [--format] flag. tcpsubnet uses the same flags as iperf for the unit
format and adds mM. When using kmKM, the output will be rounded to floor.
# tcpsubnet -fK
[03/05/18 22:44:04] 1
[03/05/18 22:44:05] 5
[03/05/18 22:44:06] 31
Just like the majority of the bcc tools, tcpsubnet supports -i and --ebpf
It also supports -v [--verbose] which gives useful debugging information
on how the subnets are evaluated and the BPF program is constructed.
Last but not least, it supports -J [--json] to print the output in
JSON format. This is handy if you're calling tcpsubnet from another
program (say a nodejs server) and would like to have a structured stdout.
The output in JSON format will also include the date and time.
# tcpsubnet -J -fK,
{"date": "03/05/18", "entries": {"": 2}, "time": "22:46:27"}
{"date": "03/05/18", "entries": {}, "time": "22:46:28"}
{"date": "03/05/18", "entries": {}, "time": "22:46:29"}
{"date": "03/05/18", "entries": {}, "time": "22:46:30"}
{"date": "03/05/18", "entries": {"": 0}, "time": "22:46:31"}
{"date": "03/05/18", "entries": {"": 1}, "time": "22:46:32"}
{"date": "03/05/18", "entries": {"": 18}, "time": "22:46:32"}
# ./tcpsubnet -h
usage: [-h] [-v] [-J] [-f {b,k,m,B,K,M}] [-i INTERVAL] [subnets]
Summarize TCP send and aggregate by subnet
positional arguments:
subnets comma separated list of subnets
optional arguments:
-h, --help show this help message and exit
-v, --verbose output debug statements
-J, --json format output in JSON
-f {b,k,m,B,K,M}, --format {b,k,m,B,K,M}
[bkmBKM] format to report: bits, Kbits, Mbits, bytes,
KBytes, MBytes (default B)
-i INTERVAL, --interval INTERVAL
output interval, in seconds (default 1)
./tcpsubnet # Trace TCP sent to the default subnets:
./tcpsubnet -f K # Trace TCP sent to the default subnets
# aggregated in KBytes.
./tcpsubnet # Trace TCP sent to only
./tcpsubnet -J # Format the output in JSON.