MTU mysteries and regedit links

A problem on my home network has been solved, but not the mystery behind it. Here's the scoop. My wife's studio is on the other end of the house from my office, where the Ethernet hub and the Linksys router live. She'd been getting great downloads, but crummy uploads. Really crummy, worse than 28.8-dialup. Here's the setup:

+-----+              +----+   +-------+  
|WinXP|--A--90ft--B--|hub |---|Linksys|
+-----+              +----+   +-------+

When I attach my PowerBook to point A, I see the same syndrome. When I attach my PowerBook to point B, no problem. Gotta be the wiring, right? Of course, I've lost the charger for my old Microtest Compas, a network tester that was cool in its day (TCP/IP and IPX/SPX, woo hoo). While I dilly-dallied about how to replace it, my wife (aka the shoemaker's barefoot spouse) had a couple of bad days when outbound email was not just slow, but actually stalled.

To the rescue came Paul Venezia, who lives and breathes networks. While charging up his tester, he got to wondering about MTU (Maximum Transmission Unit) settings. The Ethernet default, 1500, wasn't causing any trouble for devices on my end of the suspect cable, but it turns out that on the other end, 1470 is the magic number. And no, this isn't a PPPoE situation, in case you're wondering. And, by the way, the cable tested fine.

So problem solved, marriage saved. But mystery unsolved. Why does MTU 1500 at point B need to become MTU 1470 at point B? Well, perhaps the Lazy Web will tell us. Meanwhile, though, I can't resist putting in another plug for an idea I had long ago:

Many of NT's admin tools are primarily navigators and editors of specialized information spaces. A web-enabled User Manager would be able to remember and replay paths through its space -- the directory -- using bookmarks. The tool most in need of this capability isn't User Manager, though. It's RegEdit, the registry editor. Spend a day within earshot of an NT administrator and you'll hear mantras like this chanted repeatedly: "HKEY_LOCAL_MACHINE, System, CurrentControlSet, Services, W3SVC, Parameters..." Once the target key is found and altered (and the machine has been rebooted), the problem may still not be solved. So the administrator must repeat the same mantra and travel the same path to the same registry key for another try. This is nuts! In web mode, you'd bookmark that page after the second or third visit to it. [Practical Internet Groupware, Chapter 14, Automating Internet Components]

I wrote those words five years ago. But here we are, still transcribing registry keys, and still chanting. In his wonderful analysis of Apple's iTunes Music Store URI, Tim Bray frowns on the gratuitous new itms: scheme. I agree. As Tim points out, http: plus a media type is the better way, given that what's behind that itms: URI is just XML that a browser might want to use directly.

I'm not sure that application-specific schemes are always wrong, though. For an upcoming O'Reilly Network column in which I learn how to extract, index, and search my Outlook mail, I was reminded that these protocols:

outlook:/Personal Folders/Inbox/Infoworld

jump you directly into an Outlook folder or message. This is darned useful.

Take a look at this MTU-tweaking page, which as Paul observed, is tagged as popular. Some sites go so far as to provide reg-tweaking utilities, but why can't the pages that describe how and why to do the tweaking also jump you straight into the appropriate regedit locations?

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