DHCP Overview, Motivation, History and Standards
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BOOTP represents a significant improvement over RARP because it solves so many of RARP's problems. BOOTP is a higher-layer protocol, not hardware-dependent like RARP. It can support sending extra information beyond an IP address to a client to enable customized configuration. Also, through the use of BOOTP relay agents, it allows a large organization to use just one or two BOOTP servers to handle clients spread out over many physical networks.
In so doing, BOOTP effectively solves one of the major classes of problems that administrators have with manual configuration: the I have to go configure each host myself issue. It allows dumb (storageless) hosts to configure themselves automatically, and saves techies the hassles of needing to trek to each host individually to specify important configuration parameters.
BOOTP normally uses a static method of determining what IP address to assign to a device. When a client sends a request, it includes its hardware address, which the server looks up in a table to determine the IP address for that client. (It is possible for BOOTP to use other methods of determining the relationship between an IP and hardware address, but static mapping is usually used.) This means BOOTP works well in relatively static environments, where changes to the IP addresses assigned to different devices are infrequent. Such networks were basically the norm in the 1980s and early 1990s.
Over time, many networks quickly started to move away from this model, for a number of reasons. As computers became smaller and lighter, it was more common for them to move from one network to another, where they would require a different address using the new network's network ID. Laptop and even palmtop computers could literally move from one network to another many times per day. Another major issue was the looming exhaustion of the IP address space. In many organizations, permanently assigning a static IP address to each and every computer that might connect to their network was a luxury they could not afford.
In many organizations, trying to keep track of constant IP address changes became a daunting task in and of itself. BOOTP, with its static table of mappings between hardware addresses and IP addresses, simply wasn't up to the task. It also offered no way to reuse addresses; once an address had been assigned, a device could keep it forever, even if it were no longer needed.
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