In this chapter, you learned the fundamentals of IP and its addressing structure. IP can communicate across any set of interconnected networks, but is not a reliable datagram service; it is a best-effort delivery. An IP address is 32 bits, which includes a network address and a host address.
You also learned about subnets, subnet masking, variable-length masking, and why they are necessary. Subnets provide flexibility to a network by dividing a large network into smaller units, so that the entire network is not restricted by one network address. Subnet masking is performed by borrowing bits from the host portion of the assigned network address, so that more routable network addresses may be assigned within the network address. Variable-length masking is crucial for preserving valuable address space and to allow continued growth of a network.
Another area covered in this chapter is Classless Interdomain Routing. CIDR controls the size of Internet routing tables. It assists the ISP environment by limiting the number of routes advertised, which is done by condensing the number of contiguous prefixes that ISP must advertise.
Finally, you were introduced to the two types of major routing processes currently used on the Internet: Interior Gateway Protocols and Exterior Gateway Protocols. IGPs include RIP, OSPF, IS-IS and EIGRP; EGPs include only BGP. You will read about each of these in more depth in the following chapters.
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