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The central file that controls your resolver setup is host.conf.
It resides in /etc and tells the resolver which services
to use, and in what order.
Options in host.conf must occur on separate lines. Fields may be
separated by white space (spaces or tabs). A hash sign (#)
introduces a comment that extends to the next newline.
The following options are available:
- order
- This determines the order in which the resolving services are tried. Valid options are :
- bind for querying the name server
- hosts for lookups in /etc/hosts
- nis for NIS lookups.
- Any or all of them may be specified. The order in which they
appear on the line determines the order in which the respective
services are tried.
- multi
- Takes on or off as options. This determines if a host in
/etc/hosts is allowed to have several IP addresses, which is
usually referred to as being ``multi-homed''. This flag has no
effect on DNS or NIS queries.
- nospoof
- As explained in the previous chapter, DNS allows you to find
the hostname belonging to an IP address by using the in-
addr.arpa domain. Attempts by name servers to supply a false
hostname are called ``spoofing''. To guard against this, the
resolver may be configured to check if the original IP address
is in fact associated with the hostname obtained. If not, the
name is rejected and an error returned. This behavior is
turned on by setting nospoof on.
- alert
- This option takes on or off as arguments. If it is turned on,
any spoof attempts (see above) will cause the resolver to log
a message to the syslog facility.
- trim
- This option takes a domain name as an argument, which will be
removed from hostnames before lookup. This is useful for hosts
entries, where you might only want to specify hostnames with-
out local domain. A lookup of a host with the local domain
name appended will have this removed, thus allowing the lookup
in /etc/hosts to succeed.
trim options accumulate, making it possible to consider
your host as being local to several domains.
A sample file for vlager is shown below:
# /etc/host.conf
# We have named running, but no NIS (yet)
order bind hosts
# Allow multiple addrs
multi on
# Guard against spoof attempts
nospoof on
# Trim local domain (not really necessary).
trim vbrew.com.
Andrew Anderson
Thu Mar 7 23:22:06 EST 1996
