[lug] what is port 3 good for?

[D. Stimits]

Deva Samartha wrote:
> 
> something is sending packets out with port 3 and they
> get denied by the firewall outgoing to the internet.
> 
> the /etc/services says:
> 
> compressnet       3/tcp                 # Compression Process
> compressnet       3/udp                 # Compression Process

I have no reference to that service on my RH 6.2 machine. But if
something is going out on port 3, it doesn't mean anything; what really
matters is if the destination is port 3. I have no idea of what is going
on is good or bad there, but check out "fuser" and "lsof" commands to
dig in some more on what is using the port.

D. Stimits, stimits at idcomm.com

> 
> it looks it is the postfix mail demon sending out to
> mail servers it is sending mail to.
> 
> At one point, I had three packets per second going out and thought
> there was a compromise going on and shut the internet down.
> 
> Somewhere I read about this being used for a commercial product
> checking if email can be transferred compressed.
> 
> Is it safe to open this port up?
> 
> thanks,
> 
> Samartha
> 
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