Maintaining strong consistency for the identifier-to-locator mapping cache

The Locator/ID Separation Protocol (LISP) is recognized as a promising solution to address the routing scalability issues in the current Internet. In the LISP network, an Ingress Tunnel Router (ITR) usually caches recently used identifier-to-locator mappings of remote hosts. When a Mobile Node (MN) or a subnet moves across Egress Tunnel Routers (ETRs), its mapping changes. The ITRs caching the mapping need to be informed to maintain the cache consistency. In general, the mapping cache supports weak cache consistency by using the Time-To-Live (TTL) mechanism. However, a stale mapping could lead the packets to a wrong destination. With the increase of mobile users, maintaining strong mapping cache consistency has become an indispensable mechanism in the LISP network. In this paper, we first calculate the mapping change frequency caused by mobility to quantitatively characterize the mapping dynamics. Then we design the lease algorithm to realize the strong consistency and propose analytical models to decide the lease duration based on the state space overhead and the control message overhead, respectively. We present numerical results to estimate the mapping change frequency, to show the impact of different parameters on the lease duration and to explore the relationship between the state space and control message overhead. Finally, we do trace-driven simulation to compare the lease algorithm to the polling-every-time and invalidation mechanisms in terms of the state space and the control messages. The lease algorithm with an appropriate lease duration can balance the state space overhead and the control messages while providing strong mapping cache consistency.