Netcat - socket in time_wait when echoing and piping, but not when invoked directly

Question

I'm testing an application using netcat (nc) and I'm getting very low throughput on network connections. When I ran netstat -tnpo I see numerous TCP sessions in TIME_WAIT. I'm sending data to my application via a bash script as indicated below:

while true; do
    echo "<required string>" | nc server_ip port
done

If I instead do this at the terminal:

nc server_ip port
<required string>

the connection terminates immediately and there is no TCP session left in TIME_WAIT.

Why the difference? What do I need to do differently to ensure that after each echo, no TCP port is left in TIME_WAIT?

Hmmm - my version of netcat (**netcat-openbsd** `1.105-7ubuntu1`) doesn't have that option. — AnthonyK, Jan 07 '16 at 06:16

score -1 · Answer 1 · answered Jan 07 '16 at 05:04

-1

You may want to use it like this.

    while true; do
        echo "<required string>" | nc server_ip port < /dev/null   
    done

Apologies I don't have enough repo to post it like a comment.

answered Jan 07 '16 at 05:04

tollboy

76
1
8

What's the point of both piping something to `nc` and redirecting its input from `/dev/null`? – David Schwartz Jan 07 '16 at 05:39
@tollboy Same result anyway – AnthonyK Jan 07 '16 at 06:19

Netcat - socket in time_wait when echoing and piping, but not when invoked directly

1 Answers1