[Ndn-interest] Label swap vs PIT (was Re: Largest DDoS attack ever delivered by botnet of hijacked IoT devices)
ravi.ravindran at gmail.com
Wed Sep 28 16:57:59 PDT 2016
Interesting discussion on various aspects of PIT. Just wanted to add that,
usefulness of PIT should also seen in the light of real-time communication
where latency is very critical. In such systems one would pre-fetch content
even before it is produced (to achieve a PUSH effect). In the Audio/Video
conferencing system we build (
and also NDN-Conf uses this feature. In such situations multicasting is
more at play here than caching, caching is more useful in case of packet
loss during the transit.
On the topic of PITless design, we have a paper coming up in this year's
Globecomm on this topic ("pit/LESS: Stateless Forwarding in Content Centric
Networks"). IMO, these solutions are more useful to realize CCN/NDN
protocol on programmable data planes like P4/PoF where the current
forwarder/control plane abstractions are not efficient to support
per-packet statefull forwarding. From a deployment perspective, we can
envision such a data plane supporting high speed name-based forwarding with
statefull forwarding restricted only to the network edge.
On Wed, Sep 28, 2016 at 2:56 PM, <Marc.Mosko at parc.com> wrote:
> This message got a bit off topic from the OP, so I label swapped the
> subject ;)
> I think preserving the possibility of symmetric paths is a significant
> feature. It is the main property that new congestion control protocols use
> and I think an attribute that deserves serious thought.
> I agree with Luca that going label swapping instead of PIT trades one set
> of features for another set of features. I think it would be useful to
> systematically list the features offered by the PIT and the features
> offered by label swapping. One could then make a principled comparison
> between them.
> I believe that the main feature lost is Interest aggregation. If one has
> caching, then I think this is a minor loss. The window for Interest
> aggregation to work is a RTT. The window for caching to work could be much
> longer. All the memory one was spending on the per-packet PIT state can
> now be used for more caching. It would be useful to look at flash crowd
> dynamics to see if even in those cases aggregation saves much compared to
> In the NDN architecture, one would also lose the PIT nonce state, but NFD
> already has a second nonce table to keep them around after a PIT entry is
> erased, so that could stay as it is. It wouldn’t be exactly like now, but
> one could probably make nonces still work if one thinks keeping them is
> worth the memory usage.
> A significant feature gained is a large reduction in memory bandwidth by
> not having to update a large data structure at wire speed. As we saw today
> from JJ’s presentation, if one uses label swapping and routing on anchor
> identifiers, then one can make the case of running on today’s forwarding
> hardware at or near full speed. Thus the time to deployment on high speed
> routers could really shrink down.
> Anyway, I think this is worth more formal study rather than this piecewise
> On Sep 29, 2016, at 5:26 AM, GTS <gts at ics.uci.edu> wrote:
> To get back to the issue of having or not having the PIT:
> Recall that this thread started with discussion of massive DoS attacks on
> the current Internet, initiated from IoT devices. It progressed to a
> of DoS attacks in CCN. It was then suggested that a PIT-less
> design might address the only glaring major type of DoS attack in CCN --
> interest flooding. I specifically say "address", not "solve" or "obviate".
> (That's because even a PIT-less design allows the producers to be
> Now, the particular PIT-less design that Cesar mentioned is this:
> It is NOT motivated solely by interest flooding mitigation. It just happens
> to be one of its features. The authors (of whom I'm one) would love to
> hear some reasoned criticism of this PIT-less design. It should be based
> on actually reading the paper.
> More generally, the PIT is currently a fundamental feature of both NDN and
> Should it even be questioned? To some true believers, this is clearly an
> IMHO, all architecture features should be up for debate and all dogmas
> ought to be questioned.
> For example, I believe that the PIT and the CACHE (for example) are not
> make an architecture Content-Centric. Either or both can be removed and
> remains would still be a Content-Centric Network (though perhaps not a
> good one).
> Finally, the PIT-less design mentioned above could well be ill-advised,
> or even totally senseless. We simply don't know yet.
> Indeed, as the paper admits, it has some problems of its own.
> Or, it might make sense in some settings, e.g., where the
> network infrastructure is mobile. Or, it might be an alternative/optional
> (BTW, it can in fact co-exist with a PIT-ful CCN).
> Gene Tsudik
> Chancellor's Professor of Computer Science
> University of California, Irvine
> On 9/27/16 10:12 PM, Luca Muscariello wrote:
> The work JJ has presented this morning is probably another interesting
> And I agree that the signal mentioned here is not a prerogative of the PIT.
> So, to stay in topic to this thread, from my point of you what JJ has
> has more compelling properties to remove the PIT than the DDoS example
> considered here.
> In JJ's proposition, you trade something for something else. It's not an
> architecture to NDN though. So we need to be careful before laying away
> pieces of the architecture. There is a price for that.
> On Wednesday, 28 September 2016, <Marc.Mosko at parc.com> wrote:
>> Removing the PIT and using, for example, a label swapping approach such
>> as J.J. Garcia-Luna-Aceves has suggested, does not remove the “signal” you
>> talk about. One could keep upstream and downstream counters for each label
>> swap identifier and see which labels are not getting downstream data.
>> I do not think the strategy of purging PIT entries based on the shortness
>> of their remaining lifetime gives you any correlation to purging attack
>> packets. First of all, an attacker could easily use a very large Interest
>> Lifetime. Well-behaved clients that are using RTT estimates in their
>> Interest Lifetime would, by definition, likely have very small margins in
>> the Interest Lifetime remaining before the Data comes back (personally, I
>> think it is a problem to make InterestLifetime based on RTT, but that’s a
>> different thread).
>> > On Sep 28, 2016, at 10:47 AM, christopherwood07 at gmail.com wrote:
>> > On September 27, 2016 at 5:14:14 PM, Christos Papadopoulos
>> > (christos at colostate.edu) wrote:
>> >> On 09/27/2016 04:59 PM, woodc1 at uci.edu wrote:
>> >>> To re-iterate Cesar’s point, as of now, there is no truly effective
>> >>> interest flooding mitigation. However, one concrete way to minimize
>> >>> the attack surface (for routers) is to get rid of the attack's root
>> >>> cause: the PIT. (Producers could still be hosed with bogus interests.)
>> >>> And since the PIT enables several important functions, other
>> >>> architecture changes will probably have to follow in its wake.
>> >> You start with what I believe to be the wrong premise: protecting the
>> >> router. In NDN we care about communication, not a single router.
>> >> Protecting a router is winning the battle but losing the war.
>> > I respectfully disagree. If the adversary takes out the producer,
>> > there is no communication. If the adversary takes out the routers
>> > adjacent or otherwise on the path to the producer, there is no
>> > communication. Protecting the router(s) is equally important,
>> > especially since it may impact more than just a single producer.
>> >> I don't understand your statement that the root cause of DDoS attacks
>> >> the PIT. The root cause of DDoS is resource exhaustion.
>> > In these attack scenarios, the PIT *is* the resource being exhausted.
>> >>> Personally, I don’t think we should settle with an architectural
>> >>> element that has a known (and quite severe) weakness simply because it
>> >>> enables some nice features in practice. The more serious design
>> >>> problems must be dealt with first, not last.
>> >> You are underestimating the importance of the signal the PIT provides.
>> >> It is an important insight into the status of communication. The PIT
>> >> does not simply enable some "nice features". Think a bit harder about
>> >> the things you can do with this signal.
>> > In most attack scenarios, yes, it tells you when bogus interests are
>> > flooding a particular prefix and otherwise when communication is
>> > failing. But consider this scenario. Suppose you have a malicious
>> > producer cooperating with one or more malicious consumers. The
>> > consumers are quickly sending interests to this legitimate producer,
>> > who responds with legitimate data. The communication is not failing.
>> > Their goal is to do nothing other than saturate the PIT of some
>> > intermediate router. Per Spyros’ follow-up suggestion, that router
>> > might kick out old, legitimate interests in favor of these malicious
>> > ones. Of course, this is fundamentally how we would expect one to deal
>> > with and manage a limited resource. So preventing this attack seems
>> > difficult for any approach. But the point is that this resource, the
>> > PIT, is easily abused in CCN/NDN.
>> > Chris
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