NAME

svcorder − Internet Name/Address resolution methods database

DESCRIPTION

The svcorder file contains information regarding the order in which lookup methods are to be used to resolve an Internet Name/Internet Address pair.  The file consists of a single record and zero or more comments separated by newline (linefeed) characters.  The single record contains the following fields:

Host lookup methods sequence string

Comment field (optional)

The fields are separated by any number of blanks and/or tab characters.  A “#” indicates the beginning of a comment; characters up to the end of the line are not interpreted by routines which search the file. 

The host lookup methods field consists of a string of one or more keys indicating the order in which lookup methods are to be tried.  The valid keys are “YP” or “yp” for Yellow Pages, “RES” or “res” for the DARPA Internet Domain Name System (DNS) resolver (resolver(3N)); and “EHOSTS” or “ehosts” for the /etc/hosts file.  A colon (“:”) is the only valid delimiter between keys.  For applications compliant with the 88open Object Compatibility Standard Networking Supplement (OCSNS), “Yellow Pages” above does not directly refer to the NFS-oriented Yellow Pages Service.  Instead, it refers to the 88open Binary Compatibility Standard Networking Supplement (BCSNS) commands bcs_cat(1), and bcs_match(1).  bcs_cat provides Yellow Pages access to hosts, network, protocol and service information on systems supporting Yellow Pages, and is analogous to the ypcat(1) command.  bcs_match provides Yellow Pages access to the hosts database, and is analogous to the ypmatch(1) command. 

This file is accessed by the __order_init(3N), gethostbyaddr(3N) and gethostbyname(3N) function calls.  These calls read the host lookup methods string to determine the order in which resolution methods are to be attempted.  Specific ordering of lookup methods may improve the performance of applications using these functions. 

The recommended ordering for systems using the DNS resolver would be “res” first and then “yp” if Yellow Pages exists and finally “ehosts”.  If only Yellow Pages is configured on a system, the ordering “yp:ehosts” is then recommended for optimal lookup performance. 

NOTES

The existence of this file is optional.  If it does exist, this file must be readable by all users on the system.  If this file does not exist, __order_init(3N), gethostbyaddr(3N) and gethostbyname(3N) will use the following default order of lookup methods:

Yellow Pages
Hosts file lookup

For OCSNS compliant applications, the default order of lookup methods changes to:

Yellow Pages
Hosts file lookup
DNS resolver

The use of the DNS resolver is mandated by the Internet (RFC 1123 Requirements for Internet Hosts − Application and Support).  Accordingly, systems connected to the Internet must edit /etc/svcorder to ensure the DNS resolver is used. 

FILES

/etc/svcorderHostname lookup order database
/etc/hostsHosts database

SEE ALSO

bcs_cat(1), bcs_match(1), __order_init(3N), gethostbyaddr(3N), gethostbyname(3N), resolver(3N), hosts(4C)
/usr/doc/rfc1123.lprRequirements for Internet Hosts − Application and Support
The Name Server chapter in the CX/UX Networking Reference Manual.

CX/UX Networking