A method and apparatus for looking up a key associated with a packet to determine a route through a routing device, the method including, upon receipt of a key, forward traversing one or more nodes which make up a trie stored in a memory by evaluating at each node traversed a bit in the key as indicated by a bit-to-test indicator associated with each node. A value of the bit in the key determining the path traversed along the trie. The method includes locating an end node having a route and comparing the route to the key. If they match, destination information associated with the end node is outputted to guide the transfer of the packet through the routing device. If they do not match, the trie is traversed backwards to locate a best match for the key.