# Source-routed URLs

lazear@gateway.mitre.org
Fri, 30 Sep 94 14:53:45 -0400

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    From: lazear@gateway.mitre.org

    Message-Id: <9409301853.AA15196@dockside.mitre.org.mitre.org>

    To: www-security@ns1.rutgers.edu

    Subject: Source-routed URLs

    Date: Fri, 30 Sep 94 14:53:45 -0400

In doing some proxy testing related to firewalls, I have a
question about how URLs are "stacked" to provide source routing and
indirection. The schemes that I see seems to be fairly new and I'd
like some clarification.

There are two constructs. The one used by HTTP seems to be merely to
prepend the protocol and host part of each hop's URL to the front of
the destination URL. Each hop receives the stacked URLs and strips
off its part of the address, passing on the remaining part of the
URL, until a hop realizes that the destination file is local.
An example of going through a relay to the document on a real system:

http://relay.sys.org/http://real.sys.org/document.html

The other construct is used by Gopher and uses percent signs to
separate pieces. This construct is less clear to me. Here's a
live example of such a URL:

gopher://host.sys.com/0ftp%3aftp.host.sys2.com%40/dir/file

Could someone please explain the percent construct?

Could we also discuss why the two constructs for stacking URLs
need to be different? Is there an effort to make them the same?
Is this an area for an IETF working group?

While some may scoff at needing source routed URLs, because they
think that firewalls are a temporary solution, I believe that
firewalls are always going to be needed in some form and that
the indirection provided by stacked URLs are crucial to living
with firewalls and other policy-enforcement mechanisms.

Walt

PS - Unfortunately, WAIS does not use URLs, so their destination description
is different. Within the "source route" part, they separate hops with
colons, but at least they can do indirection, which helps steer queries
to firewalls and beyond.

PPS - What is the sharp-sign construct, by the way? In a URL, it appears
after the document filename:

http://host.sys.com/directory/document.html#Directives

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