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Re: Proxies and loops

From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Date: Sun, 17 Dec 1995 12:00:43 +0100 (MET)
Message-Id: <199512171100.MAA01024@labinfo.iet.unipi.it>
To: Duane Wessels <wessels@colorado.edu>
Cc: mogul@pa.dec.com, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
> First, I apologize for jumping into the middle of this thread.  I'd like
> to make a couple of comments about how TTL and Forwarded are relevant
> to the Harvest cache.
> A TTL header would not help Harvest to eliminate loops.  When the
> loop is completed and the cache gets a second request for the same URL,
> this second client-side request becomes "attached" to the first request
> (on the server-side).  The caches will deadlock until one of them times
> out.  The forwarded header would solve this problem quite easily
> (except for the hassle of parsing it).

At first I thougt that deadlocks would only occur when a node in the
loop finishes it resources (be them connections, processes, whatever).
I thought that there were *many* of them, so a suitable TTL would avoid
deadlocks. This looks like the same problem, except that there is
exactly *one* resource on each node.

> I totally agree that a HTTP-traceroute will be very useful.  However, I
> don't think we need TTL to do it.  If I understand correctly,
> traceroute uses increasing TTLs because the IP LSRR option is/was not
> always implemented, and the fixed IP header size limit only allowed
> something like nine addresses to be recorded.  Since HTTP doesn't
> suffer from either of those problems, wouldn't it be better to just
> have the Forwarded lines included in the response header?  Then you
> only need to make one request.

Convincing arguments!

Luigi Rizzo                     Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it       Universita' di Pisa
tel: +39-50-568533              via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522              http://www.iet.unipi.it/~luigi/
Received on Sunday, 17 December 1995 03:12:45 UTC

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