In the present contest by the term packet destination address it is meant the destination IP address or other known related protocol fields that may be used for routing. In the case of an IP address the packet destination address comprises, starting from bit 0, i.e. the more left bit, referred in this description also as most significant bit (MSB):                a first portion comprising a fixed number of bit which identifies the class of the supernet or subnet address,        a second portion comprising the supernet or subnet address.        
The above mentioned fixed number of bit is 1, 2, 3, 4, 5 bit for, respectively, classes A, B, C, D, E. Therefore, to each IP address it may be associated a fixed value indicating the smallest bit index of the portion of the packets destination address containing the IP address.
In the present contest by the term “routing” it is meant the operation by which, starting from a packets destination address, i.e. an IP address, a search in a data base, i.e. a routing table, is made for an entry that matches an address portion contained in said packets destination address. In particular the search may be a search for the longest entry that matches an address portion contained in said packets destination address, this kind of routing will be referred in the present contest as best prefix matching routing.
The routing table search process is the most important operation in the IP routing method. When an IP address, identified in the current IP version 4 implementations by a unique 32-bit field, is received by a router, the network prefix contained in this address must be considered in order to search in a forwarding table using the network prefix as its key and in order to determine which entry in the table represents the best route for the address to take in its journey across its destination. For optimising the searching procedure, known procedures provide compressing the network prefix in order to perform the search in a table having a limited size. Many compression methods are known. In particular, we will refer to a method based on predictable duration algorithms, and among this class of algorithms to the algorithms suitable of a pipelined implementation. In particular, we will refer to the pipelined algorithm based on the CSSA method (clustered sequential search algorithm) described in EP0.978.966 A1.
In the present contest by the term pipelined method it is meant a routing or compression method which allows a plurality of address which has to be routed or compressed to be present at the same time in the hardware implementation of said method, i.e. a method which allows to issue a routing or compression request if a previously issued one has not been served yet.
On the other hand, in order to overcome the known problem of running out of address space (ROADS problem) there have been introduced subnet and supernet IP addresses, which will be referred to further in the application as classless address.
Not all the routing and compression methods can handle classless address. In particular, the above-mentioned CSSA method cannot handle these addresses.