Both HNCP and Babel carry their control data in IPv6 packets with a link-local source address, and implementations are required to drop packets sent from a global address. Hence, they are only susceptible to attacks from a directly connected link on which the HNCP and Babel implementations are listening.
The security of a Homenet network relies on having a set of "Internal", "Ad Hoc", and "Hybrid" interfaces (Section 5.1
of RFC 7788
) that are assumed to be connected to links that are secured at a lower layer. HNCP and Babel packets are only accepted when they originate on these trusted links. "External" and "Guest" interfaces are connected to links that are not trusted, and any HNCP or Babel packets that are received on such interfaces are ignored. ("Leaf" interfaces are a special case since they are connected to trusted links, but HNCP and Babel traffic received on such interfaces is ignored.) This implies that the security of a Homenet network depends on the reliability of the border discovery procedure described in Section 5.3
of RFC 7788
If untrusted links are used for transit, which is NOT RECOMMENDED
, then any HNCP and Babel traffic that is carried over such links MUST
be secured using an upper-layer security protocol. While both HNCP and Babel support cryptographic authentication, at the time of writing, no protocol for autonomous configuration of HNCP and Babel security has been defined.