Confusing Firewall entry

Going forward, I was not going to borrow trouble looking at firewall logs. But prior to that decsion I did notice something very puzzling and a little concerning

 

It seems that when my computer is scheduled to check for microsoft updates, there will be an odd entry in my firewall log

For illustrative purposes, lets say

 my current IP address is 66.141.168.166

 

so prior to the microsoft update check, my firewall log will show

 Port Blocking allowed 66.141.168.255(3)

where the IP address is similar to mine, but ends in 255 rather than 166 and appears to use port 3(?)

Now I know that IP addresses ending in .255 are like broadcast message from the ISP used to connect to all IP address from 66.141.168.1 through 66.141.168.254 (whatever that means and whatever that is for)

But the main question I have is why would IP address  66.141.168.255(3) be showing everytime there is a scheduled check for windows update??why would my ISP have anything to do with that?

Surely it is not a coincidence each and every time?? And it only seems to happen when my computer automatically initiates the check for windows updates,  not if I run a manual check  for updates

(by the way, updates do get downloaded when they are found and connections to microsoft are noted in the internet connection log)

If anyone can help me understand it, I'd be grateful.

Thanks