Blocking port 7 from latency probes...

[Jeff Taylor]

>    Jeff> I am all in favor of latency testing throughout the Internet. In
>    Jeff> fact, I have a box on my network now that is dedicated as a probe
>    Jeff> for a project on Internet2. Why not try to marshall support for a
>    Jeff> standards based probe array instead of just scanning what ever
>    Jeff> will answer. Is that to much to ask?
>
>(Does this really have anything to do with bind?)

I think it does since the probes originate on port 53 & are targeting
the echo port on dns servers. 

>I won't attempt to justify DoubleClick's use of port 7 or their attitude
>about it.  I will point out how/why I use port 7 as a "ping" port.

The "attitude" came mostly from Resonate, the makers of Global
Products. DoubleClick just very quickly deferred all technical
questions to Resonate.

>
>I developed and maintain a distributed concert database.  All communications
>between servers is done using XML-RPC (http://www.xmlrpc.com/ for the
>curious).  The servers are not multi-threaded, so I can't have them stall
>while trying to talk to each other because they won't be able to respond to
>queries.  Consequently, I needed a simple, fast way to decide if a
>downstream server was up before making a remote procedure call.  UDP (not
>TCP) to port 7 served nicely for a few reasons:

Wow, that sounds cool. I'll have to check it out. 
Thank you, you help me make my point. You are using ports on machines
that you manage. 

>
>    1. I felt it would be the fastest way to check if a remote server was
>       up.
>
>    2. I didn't have to learn how to generate and send ICMP echo packets
>       from Python (my chosen application language in this case).
>
>    3. I felt that since on most Unixen port 7 echo code seems to be built
>       directly into inetd, not only would I get good performance, I'd be
>       accessing a piece of server code that was fairly well beat upon and
>       debugged already.  The alternative would be to pick an arbitrary
>       high-numbered port and hang a homebrewed UDP echo server off of that.
>       Consequently, enabling it on my servers probably wasn't going to
>       increase my vulnerability to attack.
>
>Skip Montanaro | http://www.mojam.com/
>skip at mojam.com | http://www.musi-cal.com/
>847-971-7098   | Python: Programming the way Guido indented...
>
>