Friday, September 25, 2020
Wednesday, September 23, 2020
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 126.96.36.199. 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.