ipnodes(4) File Formats ipnodes(4)
ipnodes - local database associating names of nodes with IP addresses
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
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:
IP-address official-node-name nicknames...
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
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 contain-
ing 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:
o The conventional "decimal dot" notation and interpreted using the inet_addr routine from the Internet address manipulation library,
o The IP Version 6 protocol [IPV6], defined in RFC 1884 and interpreted using the inet_pton() routine from the Internet address manipu-
lation 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
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.
Example 1: A Typical Line from the ipnodes File
The following is a typical line from the ipnodes file:
2001:0db8:3c4d:55:a00:20ff:fe8e:f3ad myhost # John Smith
getipnodebyname(3SOCKET), inet(3SOCKET), nsswitch.conf(4), resolv.conf(4), hosts(4)
Braden, B., editor, RFC 1123, Requirements for Internet Hosts - Application and Support, Network Working Group, October, 1989.
Harrenstien, K., Stahl, M., and Feinler, E., RFC 952, DOD INTERNET HOST TABLE SPECIFICATION, Network Working Group, October 1985.
Hinden, R., and Deering, S., editors, RFC 1884, IP Version 6 Addressing Architecture, Network Working Group, December, 1995.
Postel, Jon, RFC 921, Domain Name System Implementation Schedule -- Revised, Network Working Group, October 1984.
IPv4 addresses can be defined in the ipnodes file or in the hosts file. See hosts(4). The ipnodes file will be searched for IPv4 addresses
when using the getipnodebyname(3SOCKET) API. If no matching IPv4 addresses are found in the ipnodes file, then the hosts file will be
searched. To prevent delays in name resolution and to keep /etc/inet/ipnodes and /etc/inet/hosts synchronized, IPv4 addresses defined in
the hosts file should be copied to the ipnodes file.
SunOS 5.10 15 Dec 2004 ipnodes(4)