dy tagged every incoming packet the router receives. Therefore, the locally kept correspondence table will simply need to match the content of the tagged label with the router's output ports to find the cor- rect one. If the label is 69451, for instance, it may indicate according to the label table that the packet must be forwarded to the output port 34, no questions asked. In the strict sense of the term, classifi- cation is therefore not a problem for this realm. The original routing on the Internet was built on class-based addressing. For more details, consult the book Routing in the Internet by Christian Huitema. Four major classes of 32-bit addresses were devised in what we now call IP version 4 (IPv4). For convenience, the industry uses the dotted quad notation-for example, 128.23.34.5. This notation represents addresses as integers (distinct points) on the IP address line-in other words, a closed segment (including its two boundaries) between 0 and 232. Therefore, addresses assumed the form K.L.M.N, which corresponds to the number K X 224 + L + M 28 + N. The first possible address is 0.0.0.0 on the left side of the fictitious IP address axis segment, whereas the end address is 255.255.255.255 on the right side of the segment. As shown in Figure 13.2, class A addresses occupy the space between 0.0.0.0 and 128.0.0.0, whereas class B addresses occupy the space between 128.0.0.0 and 191.255.255.255. Class C addresses are between 192.0.0.0 and 223.255.255.255, whereas class D addresses are between 224.0.0.0 and 239.255.255.255 for multicast. Class E addresses between 240.0.0.0 and 255.255.255.255 remain reserved. The concept of the network ID (netid) was established to enable organizations to manage their own internal addresses. In class A addresses, the netid was between bits 1 and 7, whereas in class B addresses, the netid was between bits 2 and 15. In class C addresses, the netid was supposed to be sit- uated between bits 3 through 23 in an address. However, the problem was that the address space avail- able