[Ndn-interest] Valid Data packet from non-existing FIB Interface

David R. Oran daveoran at orandom.net
Mon Apr 9 05:15:54 PDT 2018

On 9 Apr 2018, at 5:30, Boubakr Nour wrote:

> Dear all,
> What is the normal behavior of an intermediate node when receiving a 
> Data packet for a valid entry in PIT, from an interface does not used 
> in the Interest forwarding of the received content.
> For example, the node receives two requests for content “n1” from 
> interfaces “f1” and “f2”. According to FIB, the Interest is 
> forwarded using interface “f4” (only "f4" can be used to reach 
> "n1"). However, a Data packet for “n1” has been received from 
> interface “f3”.
> Should we consider it as an unsolicited data packet regardless the 
> name already exists in PIT table?
Yes, I believe so, as otherwise an off-path forwarder could pollute 
caches and/or deny service to consumers.

A grey area is the case of a data packet received by an interface which 
is a VALID FIB interface for an interest, but on which a particular 
interest was not forwarded. It might be ok to relax the rule for that 
case, at some cost to performance to do the extra lookup.

Another potential scenario (not discussed anywhere in the NDN design as 
far as I can remember) are whether you can have unidirectional 
interfaces, which are useful under some limited but highly useful cases, 
such as satellite broadcast with terrestrial return. For this scenario 
the FIB needs to be structured with paired interfaces such that the 
forwarder can match incoming data over one interface with interests sent 
over a different one.

> If not how can map the allowed interface from FIB table with the 
> received ones in PIT table? (FIB table is not involved in Data 
> forwarding).
There are ways around this - you can pre-populate the PIT with the valid 
interface ids from the FIB when you forward the interest.

> Warm regards,
> Nour

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