How to make sure 443 port is open

catiewong · 10-24-2018, 05:56 AM

I will install SSL cert to my web server .

Before I install SSL cert , I would like to confirm our firewall is opened 443 port , to make sure internet can pass through our firewall with 443 port , the reason to do such test is if it is not opened , then ask the network admin to open it .

Would suggest how to do such test ?

pan64 · 10-24-2018, 06:06 AM

https://is.gd/LGXhHH

what did you try already?

bradvan · 10-24-2018, 06:13 AM

Are you talking about the port being open on the server itself, or the port being opened on an external firewall, for example? The simplest way to try is from an external host, telnet to your target host on port 443. If you connect, then it is opened.

scasey · 10-24-2018, 07:38 AM

Quote:

Originally Posted by catiewong

...the reason to do such test is if it is not opened , then ask the network admin to open it .

Ask the network admin if it is open...?

berndbausch · 10-24-2018, 08:02 AM

Quote:

Originally Posted by catiewong

Would suggest how to do such test ?

Try to access the port. If there is not answer at all, it’s probably closed. If you get “connection refused”, the port is open, but no process is listening.

Or use netcat to listen:

Code:

nc -l 443

then connect from outside and see if the connection goes through.

Best to ask the network admin though. Who knows, perhaps the port is open today and closed tomorrow.

bradvan · 10-24-2018, 09:42 AM

Catiewong, if you are talking about an external firewall, you can certainly ask the firewall admins if that port is open. However, if you don't have anything listening on your server on port 443, then testing is meaningless. The port might be open on the firewall, but your test will fail if nothing is listening.

Habitual · 10-24-2018, 05:11 PM

https://portchecker.co

443 may not be opened until after the cert is installed.

average_user · 10-24-2018, 05:34 PM

You can also use nmap to check if a port is open on a given host, for example:

Code:

$ nmap www.linuxquestions.org -p 443

Starting Nmap 7.12 ( https://nmap.org ) at 2018-10-25 00:34 CEST
Nmap scan report for www.linuxquestions.org (75.126.162.205)
Host is up (0.15s latency).
PORT    STATE SERVICE
443/tcp open  https

Nmap done: 1 IP address (1 host up) scanned in 0.51 seconds

catiewong · 10-25-2018, 01:22 AM

Quote:

Originally Posted by average_user

You can also use nmap to check if a port is open on a given host, for example:

Code:

$ nmap www.linuxquestions.org -p 443

Starting Nmap 7.12 ( https://nmap.org ) at 2018-10-25 00:34 CEST
Nmap scan report for www.linuxquestions.org (75.126.162.205)
Host is up (0.15s latency).
PORT    STATE SERVICE
443/tcp open  https

Nmap done: 1 IP address (1 host up) scanned in 0.51 seconds

if I would like to test the 443 pass through the firewall instead of localhost test , how to do it ?

JJJCR · 10-25-2018, 08:19 PM

Quote:

Originally Posted by catiewong

if I would like to test the 443 pass through the firewall instead of localhost test , how to do it ?

you want to know whether the port is open to the Internet?

If yes, try this site: https://www.portchecktool.com/

It will check whether the port is open on the firewall.

Of course, the port will only be open if proper configuration has been done on the firewall or router.

chrism01 · 10-25-2018, 10:50 PM

As above, from the outside try the telnet client cmd or nmap - amongst others.

From on the machine, as root, "netstat -tanp|grep 443 " to see if anything is listening.

To look at the host firewall, it may depend on the distro & version, but (as root) "iptables -nvL " definitely works on RHEL derived systems.

ibaydan · 10-25-2018, 11:29 PM

Use following command.

$ nmap 192.168.1.1 -p 443

For more information check following tutorial.

https://www.poftut.com/how-to-check-...stat-in-linux/

JJJCR · 10-26-2018, 01:11 AM

Get carried away with the port forwarding, but I think since you are browsing Linuxquestions.org.

Most probably port 443 is open, since LQ uses https.

HTTP = port 80

HTTPS = port 443

If you are browsing with sites with https, then it's confirmed 443 is open.

pan64 · 10-26-2018, 03:38 AM

Quote:

Originally Posted by catiewong

if I would like to test the 443 pass through the firewall instead of localhost test , how to do it ?

you cannot check pass through in general.
What you can do is to start an app which listens on the specified port and uses a tool from another host to check if someone gives a response from that given host/port.

If there was no app running and listening - you will get no answer.
If there was a firewall in the middle, which blocks the traffic - you will get no answer.
if there was an authentication issue anywhere - you will get no answer.
if there was a DNS related error - [probably] you will get no answer.

How to know if everything is ok? Actually it is simple, you will get a correct answer.
How to know if firewall was configured properly? Actually simple again, if you really know there is a firewall in between (the client and server) and you will get a correct answer (otherwise firewall can be totally transparent, so probably you cannot decide if there was a firewall [or more] put somewhere at all).

berndbausch · 10-26-2018, 04:07 AM

Quote:

Originally Posted by pan64

If there was no app running and listening - you will get no answer.

That is not quite correct. If there is no firewall blocking 443, the server will reply with an ICMP message, actively rejecting the connection request. The error message is usually something like "connection refused". This is different from the case where port 443 is blocked; in this case, the server appears not to exist, and you get "no route to host".