  We show that the mechanisms used in the name data networking (NDN) and the
original content centric networking (CCN) architectures may not detect Interest
loops, even if the network in which they operate is static and no faults occur.
Furthermore, we show that no correct Interest forwarding strategy can be
defined that allows Interest aggregation and attempts to detect Interest
looping by identifying Interests uniquely. We introduce SIFAH (Strategy for
Interest Forwarding and Aggregation with Hop-Counts), the first Interest
forwarding strategy shown to be correct under any operational conditions of a
content centric network. SIFAH operates by having forwarding information bases
(FIBs) store the next hops and number of hops to named content, and by having
each Interest state the name of the requested content and the hop count from
the router forwarding an Interest to the content. We present the results of
simulation experiments using the ndnSIM simulator comparing CCN and NDN with
SIFAH. The results of these experiments illustrate the negative impact of
undetected Interest looping when Interests are aggregated in CCN and NDN, and
the performance advantages of using SIFAH.
