I have recently installed Jaguar on my iBook, and I am impressed with where Apple is going with networking. The Rendezvous component of iChat, for example, makes it easy to find other iChat users on the local network, without having to log into AOL’s central chat server.

I’ve just been poking around with tcpdump and the iChat client. It appears that it’s using multicast UDP port 5353 for its transport.

When taking rendezvous offline:

10:42:59.246820 10.1.31.19.5353 > 224.0.0.251.5353: udp 56
10:43:00.090607 10.1.31.19.5353 > 224.0.0.251.5353: udp 58
10:43:00.232728 10.1.31.19.5353 > 224.0.0.251.5353: udp 58

When coming back online:

10:43:14.740378 10.1.31.19.5353 > 224.0.0.251.5353: udp 181
10:43:14.797714 10.1.19.49925 > 224.0.0.251.5353: udp 48 [ttl 1]
10:43:14.798237 10.1.31.19.5353 > 224.0.0.251.5353: udp 1427
10:43:14.798355 10.1.31.19.5353 > 224.0.0.251.5353: udp 95
10:43:14.798653 10.1.31.75.5353 > 10.1.31.19.49925: udp 426
10:43:14.800206 10.1.31.19.49925 > 224.0.0.251.5353: udp 48 [ttl 1]

…etc, for several hundred more lines, all coming from other rendezvous users (as we negotiate names, status, and those almost too cute user photos.)

A couple of us at ORA were kicking around what would be involved in getting rendezvous to find users not only on our network, but on a private network at another office. Obviously, if it’s using multicast, we’re missing each other as we’re separated by a router hop (we’re using 10.1/16 in one office, and 10.2/16 in the other.)

What about setting up multicast routing between the two networks? I’ve never done it, but it sounds like running DVMRP under Zebra on a machine on each side might do the trick.

Has anybody done this? It’d make a nifty hack to be able to get Rendezvous traffic bridged between arbitrary networks… Having multicast routed across the already forming GRE network that carries community wireless traffic cross-country would be pretty spiffy. (Think true peer-to-peer chat and file sharing, without a centralized server to login to, available at any free public wireless node…)

Has anyone found a better source of information on Multicast and Linux than the HOWTO?

Have you ever set up multicast traffic to cross a router hop? Is there an easier way to make rendezvous traffic flow between networks?

Related link: http://web.meganet.net/yeti/PCarticle.html

New OS X users are an eclectic mix of long-time Mac users, fed-up and over-licensed Windows refugees, Linux desktop junkies who are tired of defending their “No, it really doesn’t suck!” position, and of course, the old school Unix trained techno-luminati, grateful to finally have access to a GUI that isn’t XWindows.

While discussing “what makes an OS X user be like that?” around the office, I was reminded of a piece I had seen four years ago by Thomas Scoville, called The Elements of Style: Unix as Literature. I think it is just as relevant now (in a world of iBooks and OS X) as it was in 1998:

“The common thread was wordsmithing; a suspiciously high proportion of my UNIX colleagues had already developed, in some prior career, a comfort and fluency with text and printed words. They were adept readers and writers, and UNIX played handily to those strengths. UNIX was, in some sense, literature to them.”

It’s difficult to describe why using OS X is any different from using another operating system. I think one of its most beneficial effects is its ability to expose new users to the value of Unix as a system in general, and to freely available tools and APIs in particular.

It is very gratifying to hear longtime Mac users like Derrick Story find new joy in discovering commandline DNS tools like dig and nslookup, and realizing the power that lurks under the flashy dancing interactive cartoon of the Aqua interface.

I find it a very humorous irony that the ultimate tool that will likely bring people back to doing more in a Unix terminal may turn out to be the latest version of MacOS…

If you use OS X for your day-to-day work, what are you trained in? Were/are you a Comp/Sci geek, a Lit major, or something else entirely?

Related link: http://lists.personaltelco.net/pipermail/ptp/2002q3/014804.html

This just in, from PersonalTelco.

The FBI is evidently concerned about War Driving and War Chalking being used as tools for compromising corporate and other private networks.

This was just posted to PTP, apparently from Special Agent Bill Shore of the FBI. (I’d check his PGP signature, if he had used one…):

“Identifying the presence of a wireless network may not be a criminal violation, however, there may be criminal violations if the network is actually accessed including theft of services, interception of communications, misuse of computing resources, up to and including violations of the Federal Computer Fraud and Abuse Statute, Theft of Trade Secrets, and other federal violations.”

It’s certainly good to stay aware of who’s saying what about your network, but could “identifying the presence of a wireless network” really be considered a federal offense?

Should Wardriving and Warchalking be considered a federal offense?