Skip to main content

Bandwidth Measurement using netcat on Linux

There are various implementations. I am using nmap-ncat on rockOS 8 on both hosts.

Netcat's using TCP by default and this test is not limited by disk I/O from what I understood. That said, it is not the best solution, but it is a great 'quick and dirty' method. Additionally, there is no encryption overhead and no compression involved.

Important: Please use with caution. You can lose access to a host while performing the test.


Server / Receiver:
nc -k -v -l 33333 > /dev/null
-k # keeps listening after connection ends (might not be available e.g. gnu-netcat)
-v # verbose output
-l 33333 # listen on port 33333 (default TCP)
> /dev/null # send incoming data into the void to avoid disk I/O
Client / Sender:
dd if=/dev/zero bs=500M count=1 | nc -v 192.0.2.5 33333
dd # convert/copy files
if=/dev/zero # read from file, only zeros in this case
bs=500M # sets the data-/ blocksize, 500 Mibibytes, use 500MB for Megabytes,
count=1 # set the maximum number of blocks, just leave it at 1
| # 'pipes' all data to the next command
nc # netcat command
-v # set a more verbose output
192.0.2.5 # set destination server IP
33333 # set destination port

Result on the client side

[user@test-rocky-01 ~]$ dd if=/dev/zero bs=500M count=1 | nc -v 192.0.2.5 33333  
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: Connected to 192.0.2.5:33333.
1+0 records in
1+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 19.6253 s, 26.7 MB/s
Ncat: 524288000 bytes sent, 0 bytes received in 19.71 seconds.

Result on the server side

[user@test-rocky-02 ~]$ nc -k -v -l 33333 > /dev/null
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: Listening on :::33333
Ncat: Listening on 0.0.0.0:33333
Ncat: Connection from 198.51.100.19.
Ncat: Connection from 198.51.100.19:42822.
Ncat: Connection from 198.51.100.19.
Ncat: Connection from 198.51.100.19:43088.
[...]

Side note: It is recommended to test both directions.

Additional options

Side note: For security reasons on most systems you need higher permissions to use ports in the range of 0-1023 (reserved port range).

[user@test-rocky-02 ~]$ nc -k -v -l 444 > /dev/null
Ncat: Version 7.92 ( https://nmap.org/ncat )
Ncat: bind to :::444: Permission denied. QUITTING.

Specify source interface/IP:
-s 10.20.10.8
Specify source port:
-p 45454 # on the client obviously
Tip: changing the source port with every run to find a specific run faster in a packet capture
Using UDP instead of TCP:
-u # must be used on both hosts and might not be compatible with other options

Troubleshooting

Large transfer / longer test

[user@test-rocky-01 ~]$ dd if=/dev/zero bs=4G count=1 | nc -p 5555 -v 192.0.2.5 33333 dd: memory exhausted by input buffer of size 4294967296 bytes (4.0 GiB)

You are limited by your RAM when you want to send more data. You can decrease bs=4G to bs=1G, and increase the counter count=1 to 4 to transfer 4GiB of data.

Connection refused

Ncat: Connection refused. Ncat: TIMEOUT.

Make sure: - that the netcat server is running - double-check the destination host and port of the command - make sure that you can reach the destination over this port - network firewalls - routing - check both host firewalls and make sure the inbound and outbound traffic is allowed

Caution

As mentioned before, you can lose access to your hosts. Additionally, please announce tests to your network and security team as you can disrupt a productive network or trigger some kind of IDS system in place.


E-Mail hellofoo@ittafoovern.comcom
Fediverse ITTavern
Lemmy infosec.pub/c/ittavern


More reading: