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The ipnodes file is a local database that associates
the names of nodes with their Internet Protocol (IP)
addresses. IP addresses can be either an IPv4 or an IPv6
address. The ipnodes file can be used in conjunction
with, or instead of, other ipnodes databases, including the Domain Name
System (DNS), the NIS ipnodes map, and the NIS+ ipnodes table. Programs
use library interfaces to access information in the ipnodes
file.
The ipnodes file has one entry for each IP address of each node. If a node has more than one IP address, it will have one entry for each, on consecutive lines.
The format of each line is:
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IP-address official-node-name nicknames...
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Items are separated by any number of SPACE
and/or TAB characters. The first item on a line is the
node's IP address. The second entry is the node's official
name. Subsequent entries on the same line are alternative names for the
same machine, or "nicknames." Nicknames are optional.
For a node with more than one IP address, consecutive
entries for these addresses may contain the same or differing nicknames.
Different nicknames are useful for assigning distinct names to different
addresses.
A call to getipnodebyname(3SOCKET) returns a hostent structure containing
the union of all addresses and nicknames from each line containing a matching
official name or nickname.
A `#' indicates the beginning of a comment; characters
up to the end of the line are not interpreted by routines that search the
file.
Network addresses are written in one of two ways:
- The conventional "decimal dot" notation and interpreted
using the inet_addr routine from the Internet address manipulation library, inet(3SOCKET).
- The IP Version 6 protocol [IPV6], defined in RFC 1884 and interpreted using the inet_pton()
routine from the Internet address manipulation library. See inet(3SOCKET).
These interfaces supports node names as defined in Internet
RFC 952 which states:
A "name" (Net, Host, Gateway, or Domain name) is a text string up
to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus sign
(-), and period (.). Note that periods are only allowed when they serve
to delimit components of "domain style names". (See RFC 921,
"Domain Name System Implementation Schedule," for background).
No blank or space characters are permitted as part of a name. No distinction
is made between upper and lower case. The first character must be an alpha
character. The last character must not be a minus sign or period.
Although the interface accepts node names longer than 24 characters
for the node portion (exclusive of the domain component), choosing names
for nodes that adhere to the 24 character restriction will insure maximum
interoperability on the Internet.
A node which serves as a GATEWAY should have "-GATEWAY"
or "-GW" as part of its name. Nodes which do not serve
as Internet gateways should not use "-GATEWAY" and "-GW" as part of their names. A node that is a TAC should have
"-TAC" as the last part of its node name, if it is a DoD
node. Single character names or nicknames are not allowed.
RFC 952 has been modified by RFC
1123 to relax the restriction on the first character being
a digit.
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