Hazy Sighted Link State Routing Protocol - Critiques

Critiques

Because HSLS sends distant updates infrequently, nodes do not have recent information about whether a distant node is still present. This issue is present to some extent in all link state protocols, because the link state database may still contain an announcement from a failed node. However, protocols like OSPF will propagate a link state update from the failed nodes neighbors, and thus all nodes will learn quickly of the failed node's demise (or disconnection). With HSLS, one can't disambiguate between a node that is still present 10 hops away and a failed node until former neighbors send long-distance announcements. Thus, HSLS may fail in some circumstances requiring high assurance.

While the papers describing HSLS do not focus on security, techniques such as digital signatures on routing updates can be used with HSLS (similar to OSPF with Digital Signatures), and BBN has implemented HSLS with digital signatures on neighbor discovery messages and link state updates. Such schemes are challenging in practice because in the ad hoc environment reachability of public key infrastructure servers cannot be assured. Like almost all routing protocols, HSLS does not include mechanisms to protect data traffic. (See IPsec and TLS.)