Use of network_interfaces in rc.conf

[Eric W. Bates]

On 3/15/2012 7:27 PM, Kevin Oberman wrote:
> 2012/3/14 Eugene Grosbein<egrosbein at rdtc.ru>:
>> 15.03.2012 06:33, hiren panchasara пишет:
>>
>>>      network_interfaces is basically historic rudiment
>>>      used in 2.2.x FreeBSD version and alike.
>>>
>>>      In general, you should not use it in modern version at all.
>>>
>>>
>>> Thanks Eugene.
>>>
>>> So, the only way to specify boottime configuration (that survives reboots) for an interface in rc.conf is:
>>> ifconfig_em0="dhcp" ?
>>
>> Yes, thats what man rc.conf says.
>
> Minor correction, but the man page says 'ifconfig_em0="DHCP". It may
> not be case sensitive, but I have always uded CAPS like the man page
> specifies. Also, I usually end up specifying SYNCDHCP to avoid having
> something else that requires network starting before the interface is
> configured.
>
> Of course, ifconfig_* may have any valid ifconfig argument in it, but
> remember the rc.conf is shell, so you must put all of the definition
> in a single statement. You can't do:
> ifconfig_em0="DHCP"
> ifconfig_em0="mediaopt half-duplex"
> That will not do DHCP, so hte interface will not come up. Of course,
> you can concatinate a second entry to the first using normal sh
> syntax.

FreeBSD rc has a clever way around this. In /etc/network.subr 
ifscript_up(), if the file /etc/start_if.em0 is readable, it will be dot 
executed. So you can put as much multi-line config info in there as you 
would like. e.g.:

ifconfig em0 mediaopt half-duplex
dhclient em0

As long as network_interfaces includes em0 (and it will be automatically 
included by default), then start_if.em0 will be run. Conversely, 
stop_if.em0 will also run when rc runs at shutdown.