Two-layer host blocking: caching the blocking decisions

We propose a hierarchical solution to handle the rapidly-growing URL-list in Web content filtering and blocking for Web gateway appliances, in particular those for home and small enterprises. The idea behind our solution is to "cache" the blocking decision of Web access for reuse. With our proposal to integrate the first level of the blocking hierarchy into the local DNS, several advantages can be obtained: (i) high hit rate in DNS allows extremely fast blocking decisions to be obtained most of the time, and (ii) in case of DNS misses, the overlapping delay of accessing the lower level of the blocking hierarchy with delay of accessing remote DNS allows the overhead of blocking/filtering to be hidden from the user\´s experience. Both the system implementation and the experimental result are reported. The hierarchical blocking concept is important because it provides hardware constrained environments such as the TV-set-top box and home gateway with a cost effective solution for Web content blocking and filtering.