Efficient Prefix Updates for IP Router Using Lexicographic Ordering and Updatable Address Set

摘要

Dynamic IP router table schemes, proposed in the literature, perform an IP lookup or an on-line prefix update in O(log n) memory accesses. In term of lookup time, they are still slower than FEC (CNHA/CWA) scheme, which requires exactly (at most) three memory accesses for each lookup, irrespective of the number of prefixes n. The prefix update in FEC (CNHA/CWA) has a drawback: Off-line solutions need structure reconstruction, or implementing on-line prefix updates is difficult. This paper solves this problem. We propose the use of lexicographic ordered prefixes to reduce off-line construction time. Simulations on several real routing databases, run on the same platform, show that our approach constructs FEC (CNHA/CWA) tables in 2.56 to 7.74 (1.56 to 2.7) times faster than that from previous techniques. Our on-line update scheme uses an updatable-address-set and selectively decompresses the FEC and CNHA/CWA structures to modify only the next-hops of the addresses in the set. Recompressing the updated structures, the resulting tables are identical to what would have been obtained by structure reconstructions, but at much lower computational cost. Our on-line update for FEC (CNHA/CWA) scheme takes at most 10.1 (7.21) -Ýs, which is of same order as achieved by the recently proposed schemes.