ipnodes - local database associating names of nodes with IP
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 Sys-
tem (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. Sub-
sequent 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 differ-
ing nicknames. Different nicknames are useful for assigning
distinct names to different addresses.
A call to getipnodebyname(3SOCKET) returns a hostent struc-
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:
o The conventional "decimal dot" notation and inter-
preted using the inet_addr routine from the Internet
address manipulation library, inet(3SOCKET).
o The IP Version 6 protocol [IPV6], defined in RFC 1884
and interpreted using the inet_pton() routine from the
Internet address manipulation library. See
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 com-
ponents 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 restric-
tion 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:
2::56:a00:20ff:fe7b:b667 foo # John Smith
in.named(1M), 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,
Harrenstien, K., Stahl, M., and Feinler, E., RFC 952, DOD
INTERNET HOST TABLE SPECIFICATION, Network Working Group,
Hinden, R., and Deering, S., editors, RFC 1884, IP Version 6
Addressing Architecture, Network Working Group, December,
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.
Man(1) output converted with