== Multihomed hosts and _/etc/hosts_

As a side note to [[looking up hostnames from IP addresses
../programming/ReverseDNS]] for people who use _/etc/hosts_, note that
_/etc/hosts_ lookups work badly in the presence of hosts with multiple
IP address, since most _gethostbyname()_ implementations will only
return the first IP address that they find in _/etc/hosts_. These days
you really want a minimal _/etc/hosts_ and a reliable DNS server, unless
you have [[special concerns MinimalHostnames]].

(The _gethostbyname()_ behavior is sensible, since otherwise it would
always have to scan the entire _/etc/hosts_ file just to make sure that
it had found all IP addresses for a host, even when most hosts only have
one IP address.)

While there are workarounds for this issue, I think that the best
way out is just to not have any entries for your multihomed hosts in
_/etc/hosts_, even on the hosts themselves. This appears to work fine on
at least modern Linuxes, and I can't imagine that the *BSDs do any worse
here.

(You can have similar behavior with _gethostbyaddr()_, depending on
how you give an IP address multiple names in _/etc/hosts_. Putting all
the names on one line works out, but having multiple lines for one IP
address has the same problem.)