

Host names and internet addresses

A brief description of the syntax of host names and internet 
addresses, and the method by which host names are resolved.

When PC/IP network programs accept a hostname argument it may be 
in either of two standard forms:

    1)  Internet address.  An internet address is four octal 
        integers separated by commas, for example:
               22,11,0,127
        or four decimal integers separated by periods, for example:
               18.9.0.87
        Each integer represents one byte of a 32-bit standard 
        internet address, in the order "network," "subnet," etc.  
        When the user supplies an internet address the PC/IP 
        network program uses it as is, depending on nothing else 
        for name resolution.

    2)  Host name.  When a PC/IP network program encounters a 
        string that does not appear to be an internet address, it 
        interprets the string as a host name and it attempts to 
        resolve the name by appeal to one or more name servers 
        via the network.  The program sends inquiries to as many 
        as five name servers, whose internet addresses are embedded 
        in the command program.  (The user may change the number of 
        name servers and their internet addresses by use of the 
        PC/IP program "custom".)

When the user supplies a host name, there can be three outcomes,
since name servers may reply with an internet address, reply with
a "host name unknown" response, or may not reply at all.  To
increase availability several name servers are polled, and the
following rules merge the resulting replies:

    1)  If one or more name servers respond with an internet 
        address, the program uses the first such response received 
        and ignores all later responses.

    2)  If one or more name servers respond, but all the responses 
        are "host name unknown," the program displays that error 
        message and exits.

    3)  If no response arrives from any name server within five 
        seconds, the program gives up, displays the error message 
        "name servers not responding," and exits.

Note that if different name servers give different responses to 
the same inquiry, the user may see erratic results depending on 
which name servers are up and which respond more quickly.  If one 
suspects that name servers are not responding or are not in 
agreement, the command "hostname" may help isolate the trouble.


23 May 1983.  This document is in file nameres.txt
