Wednesday, September 23, 2020

Can You Ping To A Certain Port Number?

 I had a phone conversation today with someone who said that they thought that they could ping to a certain port number.  I was walking them through using telnet to see if a port was open, when that statement was made.  Thats the quick way to see if a port is open, to just telnet to that port and see if you get a blinking light.  Easy enough, but can you ping to a certain port at the destination end?

Quick answer, No.  Here is why:

Notice above how there is not port number under layer 4 (Internet Control Message Protocol).  You can see Im pinging  But you dont see any port number involved.

Now, lets look at a UDP packet:

At layer 4, you do see port numbers.  Specifically a source and destination port number.  Same for TCP, but not ICMP.  

Always prove with a packet capture.