[Ndn-interest] Data comes from another face?

Ignacio.Solis at parc.com Ignacio.Solis at parc.com
Mon Jun 8 10:51:27 PDT 2015

On 6/8/15, 10:15 AM, "Junxiao Shi" <shijunxiao at email.arizona.edu<mailto:shijunxiao at email.arizona.edu>> wrote:

Sabet's original question is asking whether a Data packet could be received on a face where an Interest has not been forwarded to, under normal situations. The question is not about whether such Data packet should be accepted.
Currently NFD forwarding would accept a Data packet as long as there is a PIT entry, without considering whether an Interest has been forwarded to the incoming face.
This behavior is inherited from ccnd 0.7.2, and I know there's a security risk.

Good thing we deprecated the old ccnd :-).

I also suspect there would forwarding problems where transmissions on a multi-access link cannot reach every node.
But I'm unfamiliar with those links, so I can't say exactly what problem could occur.

Assume a network of:   A——B——C——D  where nodes can only hear neighbors. So: A can hear B but not C.   B can hear both A+C. C can hear B+D, D can only hear C.  A is a requester, D is a producer.  A wants to get data located at D.

Case 1 - Nodes don’t forward interests over the interface they received them from.
A sends and interest and B gets it.  B needs to forward the interest, but won’t do so over the same interface it arrived on.  Protocol fails.

Case 2 - Nodes forward interest over interface they received it on + nodes don’t forward objects over same interface
A sends an interest and B gets it.  It forwards the interest.  Any node that receives the interest will forward it, flooding the network. C gets the interest, D gets the interest.   D responds.  C gets the reply satisfying the PIT from the interface that requested it. It assumes somebody else answered. - Protocol fails.
Case 2b - Nodes that receive duplicate interests (same nonce), send control message to prune
Chaos ensues as networks larger than 3 start pruning each other.  A sends to B. B sends to A+C. C sends to B+D.
B sees same interest from C, sends a prune message to C. C removes pit state.
Case 2b.1 - If there is hold time on PIT, C won’t create a PIT entry again. Protocol fails.
Case 2b.2 - If there is no hold time on the PIT entry, it may get created again as the interest is still being flooded. Network will continuously prune and flood, collapsing. - Network fails.

Case 3 - Nodes forward interest over interface they received it on + nodes forward objects over same interface
Same as Case 2, interest is flooded on the network… and then the data is flooded on the network.

I’m sure other cases exist.

These errors don’t occur if the link/interface/face has other properties. Like they can all hear each other (though there may are other issues in this scenario alone), there is an underlying protocol (like MAC level unicast), next-hops are used instead of interfaces/links/faces, etc.

Again, maybe there are NDN features I’m not aware of or forgot.  But either way, it’s a good discussion to have. And maybe you can clarify how NDN handles these cases.


On Mon, Jun 8, 2015 at 9:55 AM, <Ignacio.Solis at parc.com<mailto:Ignacio.Solis at parc.com>> wrote:
Hi folks.

I wanted to bring up a couple of important points to this discussion that have not been mentioned.  Maybe people have already assimilated them so they think they’re obvious, but just in case:

1-  A node should not accept data packets over links/interfaces/faces over which it did not forward an interest.  This is a security risk.

2- NDN may have issues over multiple access links/interfaces/faces where not all nodes can hear each other (non-infrastructure WiFi).

Both of these are true in the basic case. It’s possible that with extra design, protocols or developments that I’m unaware of these can be mitigated/solved.


Nacho (Ignacio) Solis
Protocol Architect
Principal Scientist
Palo Alto Research Center (PARC)
Ignacio.Solis at parc.com<mailto:Ignacio.Solis at parc.com>
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