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Re: Proxies and loops

From: Roy T. Fielding <fielding@avron.ICS.UCI.EDU>
Date: Mon, 27 Nov 1995 12:58:29 -0800
To: Jeffrey Mogul <mogul@pa.dec.com>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <9511271258.aa16046@paris.ics.uci.edu>
> There are two main uses for the TTL field in IP headers: first,
> to avoid routing loops and long-delayed packets.  Second, to make
> "traceroute" work.  I would bet that most TTL "failures" in today's
> Internet are from traceroute users, not routing loops.

Ummm, I thought traceroute just used this hack (useful as it is) because
there was no way to change IP to include a "traceroute" command sending
a response from each recipient.

> Traceroute has proved to be an essential tool in debugging IP-level
> problems.  We ought to be thinking about providing analogous debugging
> tools at the HTTP level.  For example, "how come the users on my
> LAN are having trouble reaching server www.xxx.com?"  It would be
> really nice to have a "trace-http-path" program, like traceroute
> but displaying the HTTP-level forwarding path instead of the IP-level
> routing path.

That is why I put TRACE in the HTTP/1.1 specification as a new method.
The only problem is that you won't get any response back from an unbounded
circular route.  I suppose we could add a Max-Forwards request header,
but I'd prefer to have an application test it out first.


 ...Roy T. Fielding
    Department of Information & Computer Science    (fielding@ics.uci.edu)
    University of California, Irvine, CA 92717-3425    fax:+1(714)824-4056
    http://www.ics.uci.edu/~fielding/
Received on Monday, 27 November 1995 13:16:56 EST

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