July 26, 2018

By Joe Winett

IN THIS ISSUE

We celebrated Independence Day in the United States three weeks ago.  Here in the Great State of Oklahoma, my neighbors still celebrate by detonating fireworks once or twice a week.  Our proud, American, outside-dogs continue to thrill to the rockets' red glare each and every time.  The outside-cats don't seem to even notice, yet I don't doubt their patriotism one bit.  I expect the celebration to continue until the autumn hunting season.

This is just a brief newsletter.  I wanted to announce completion of the first version of a new Power Tool designed to help people learn to program, but it's not nearly ready and I don't want to let July get away without sending out an issue.

Karen's Hasher Updated

Just after the last newsletter, two of Karen's Power Tools users sent in a bug report about Hasher on the same day.  Well, J.W. was resending a detailed report he had mailed many years ago, but between the two I was able to find and fix it pretty quickly.  Thank you!

Hasher saves the last directory selected for hashing files as a group or individually.  The next time you want to do the same it tries to bring up the directory again, but if it no longer exists, or was on a drive that is no longer available – such as on a removable USB drive – then a "Runtime Error 76 (path not found)" error would pop up.  The only way to make the problem go away was to manually change the registry or uninstall and reinstall the application.  That doesn't happen now.

The bug fix forced me to build a new installer, which I was able to do using Karen's original configuration scripts for NSIS, the Nullsoft Scriptable Install System, which is licensed much like other open source software.  Thanks, NSIS Team for your work on that excellent tool!

The new Karen's Hasher v2.3.1 is available for download on our website:

https://www.karenware.com/powertools/pthasher

Thought Experiment Correction

As part of the announcement in last month's newsletter of the new Power Tool, Karen's Traceroute, I spun a flawed thought-yarn experiment to explain how packets are routed around the Internet.  Don Arrowsmith noticed my faux pas and sent me a nice email explaining the issue.  Thanks, Don!   

The basics of what happens when packets are destined for a host outside of your house were correct:  Your machine sends packets to the router in your home and then the router sends them upstream.  In that scenario, your router is your default gateway; and then your router sends them to its default gateway.  However, when I described the movement of packets from your machine to another machine within your home as though those packets are IP routed through your Wi-Fi device, I was wrong.  

Your PC is configured with an IP address, plus a mask value that tells it all of the other possible IP addresses that might be in use on the same home network, and then a default gateway address on the same network to which it should send all packets destined elsewhere.  When data is destined for an IP address inside that home network, it sends the data "directly" to it via the Ethernet transport.

Ethernet is a local area networking protocol; it is not an inter-network protocol.  Ethernet frames move between machines on your home network according to MAC addresses over Wi-Fi or physical Ethernet, a transport service provided by your home network device.  They are not routed by the logical IP address so you don't see your home router's IP address as a "hop" on a traceroute to another machine at home.

A Wi-Fi router can serve all these roles at once: Layer 1, as a physical connection between your machines; Layer 2, as an Ethernet transport between your machines; and then, if data is destined for an external network, the packets are routed via Layer 3 using internetworking protocol (IP).

What are these Layers of which I've typed?  The Open Systems Interconnection (OSI) model describes how information is sent in order of layers of increasing complexity, with each higher layer depending on the proper operation of all the layers beneath it to get its own job done.

If you're interested in the ins and outs, Wikipedia has a great article about it here:

https://wikipedia.org/wiki/OSI_model

If you'd like me to write more about the guts of networking, great!  Please send me an email at joe@karenware.com (or just reply to this newsletter message).  In the future, I hope to have a "click here to vote, Yay!" button here.

Thank you!

If you see Karen around the ‘net tonight, that means your network operates above Layer 99 – God bless you.  Don't forget to wave and say, "Hi!" 

Love,
Joe


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