How to Know is a Remote hosts have open port

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# 1  
Old 10-29-2009
How to Know is a Remote hosts have open port

Hi gurus of unix!!!!, I have a little question. I nedd your helps
The scenarios is the following
I have tree equipment that are installed in different places. I use a carrier to interconnect the equipment.
Some Port's (TCP) need to be open for an application that must be function correctly.
For example:
Place 1: have the following IP
Place 2: have the following IP
Place 3: have the following IP

The application need the following port(TCP), for example 1020, 21, 53, 8080

I talk to the Network Administratos of the Carrier and he tell me that these port (TCP) are open in your firewall/router.
The question is How I verify that this port are open?,
Suppose that the application is properly installed
Help me please.
# 2  
Old 10-29-2009
Generally you can telnet to the port to see if it's open. If you get "Connection refused" that means 1) you can't get to that port/ip or 2) there's nothing listening on that port. If you are able to connect and have to break out of the telnet session you were successful.

To telnet to a specific port use:

telnet <ip> <port>


telnet 1020
telnet 21
# 3  
Old 10-29-2009
Very simple:
nmap -sS -vvv -p 1020,21,53,8080 <...>

Very, very simple, though hard to properly automate:
telnet 21
telnet 1020

Slightly more complex, but ideal for automation:
netcat -z -w 3 21 && echo "Open" || echo "Closed"

# 4  
Old 10-29-2009
mglenney, pludi
Excellent tips!!!!!!!
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