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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)

TCP/IP Name Systems: Host Tables and Domain Name System (DNS) 1 2 TCP/IP Host Table Name System

In the section that introduces name systems and describes the concepts behind them, I described an interesting paradox. Even though name systems aren't strictly necessary for the functioning of a networking system, they make using a network so much easier for people that they are considered an essential part of most networks. I think no better evidence of this can be found than the history of name system development in TCP/IP.

In fact, the history of name systems in the TCP/IP protocol suite actually goes back well before TCP and IP were themselves even created! In the late 1960s and early 1970s, when the predecessor of the Internet (the ARPAnet) was being developed, it used older networking protocols that served the same function that TCP and IP do today. The ARPAnet was very small by today's standard, containing at first only a few machines, called hosts just as TCP/IP machines often are today. The addressing scheme was also very simple: just the combination of an IMP (computer) number and a port number for each host.

With only a handful of machines names it was easy to memorize addresses, but as the ARPAnet grew to several dozen machines this became untenable. As early as 1971, it was apparent to the engineers designing the ARPAnet that symbolic names were much easier for everyone to work with than numeric addresses. They began to assign simple host names to each of the devices on the network. Each site managed its own host table that listed the mappings of names to addresses.

Naturally, the ARPAnet engineers immediately recognized the dangers of having each site maintain a list of possibly inconsistent host names. Since the internetwork was just a small “club” at this point, they used the RFC process itself to document standard host name to address mappings. RFC 226, Standardization Of Host Mnemonics, is the first RFC I could find showing how host names were assigned. It was published on September 20, 1971.

This initial name system was about as manual as a system could be. As additions and changes were made to the network, the list of host names was updated in a new RFC, leading to a series of RFCs being published in the 1970s. Each host administrator still maintained his or her own host table, which was updated when a new RFC was published. During this time, the structure of host names was still under discussion and changes were made to just about every aspect of the name system as new ideas were explored and refined.

This worked fine while the ARPAnet was very small, but had many problems. One was that it was extremely slow in responding to network modifications; additions or changes would only be entered into device tables after a new list was published. Even with the centralized list, there were also still potential consistency issues, if a site manager forgot to update a file or made a typographical error. These were in addition to the usual limitations of a host-table-based name system.

TCP/IP Name Systems: Host Tables and Domain Name System (DNS) 1 2 TCP/IP Host Table Name System