Bandwidth Measurement using netcat on Linux

CaffeineFueled

2024/01/20

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:

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.




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