You would have to identify a loop in the network first, then introduce a request with an insanely large Max-Forwards. Now, the current proxy text mandates decrementing Max-Forwards by exactly one. A network could protect itself from this kind of attack by reducing the value to something it thought was sane.
I don't see where adding Via's below ties in though. RjS > -----Original Message----- > From: Henning Schulzrinne [mailto:[EMAIL PROTECTED]] > Sent: Wednesday, January 16, 2002 1:17 PM > To: Jonathan Rosenberg > Cc: Jasson Casey; [EMAIL PROTECTED] > Subject: Re: [Sip-implementors] Max-Forwards v. Loop Detection > > > One potential issue is DOS attacks. Without loop detection, > can I inject > requests (adding Via's, say) that create additional work for > proxies, by > looping around until Max-Forwards kicks in? With a high > Max-Forwards, I > get a pretty good amplification factor. > > Jonathan Rosenberg wrote: > > > > Jasson Casey wrote: > > > > > I've been going back through the RFC(s) and have a > > > question. > > > > > > Requests can illegally loop or legitimately spiral. My > > > current understanding is that an illegal loop is > > > present when there is a corresponding via entry > > > already in the via stack, and the message has a > > > similar vector as with the previous via entry. > > > > > > What does Loop detection accomplish that cannot be > > > accomplished with the Max-Forwards field? > > > > Indeed, a fine question, and the source of Open Issue #407, which > > proposes to deprecate loop detection in favor of max-forwards. > > > > Loop detection has the benefit of detecting loops > immediately, whereas > > with Max-Forwards, they can loop around a few times till the counter > > hits zero. However, I believe experience has shown us that the > > complexities of detecting a loop vs. a legitimate spiral are > > substantial, and the small imporvement in performance it > provides is not > > worth the cost. > > > > There has been little comment on the proposal to deprecate loop > > detection; one email in favor, and a few questions. Without any > > additional comment it will be removed from bis-06. > > > > Thanks, > > Jonathan R. > > > > -- > > Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Avenue > > Chief Scientist First Floor > > dynamicsoft East Hanover, NJ 07936 > > [EMAIL PROTECTED] FAX: (973) 952-5050 > > http://www.jdrosen.net PH: (973) 952-5000 > > http://www.dynamicsoft.com > > > > _______________________________________________ > > Sip-implementors mailing list > > [EMAIL PROTECTED] > > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
