Re: Pf syntax, need help understanding an example

hi,
$ext_if -     expands to the name of the interface
($ext_if) - expands to the ip address assigned to the interface

On 06.06.18 12:21, Johan Mellberg wrote:
> Hi,
>
> I am working my way through "The Book of Pf" and got hung up on the
> example on page 31 of edition 3 (I am reading edition 2 but the
> example seems to be identical in edition 3):
>
> ext_if = "re0" # macro for external interface - use tun0 or pppoe0 for PPPoE
> int_if = "re1" # macro for internal interface
> localnet = $int_if:network
> # ext_if IPv4 address could be dynamic, hence ($ext_if)
> match out on $ext_if inet from $localnet nat-to ($ext_if) # NAT, match IPv4 only
> block all
> pass from { self, $localnet
>
> So, what it does is not a problem, I understand that, but that set of
> parentheses around $ext_if confuses me. The explanation states that
> the IPv4 address could be dynamic (which is clear...) but I look at
> that example and as far as I understand, $ext_if should expand to
> "re0", not an IP address - right?
>
> Just to test I tried a simple line in my own pf.conf (on OpenBSD 6.3):
>
> ext_if = "em0"
> set skip on $ext_if
>
> and tested with pfctl -nvf /etc/pf.conf
>
> That worked so then I put parentheses around $ext_if:
>
> set skip on ($ext_if)
>
> and tested again. This time I got a syntax error!
>
> So could someone please explain this to me? I don't think this is an
> error in the book because there is a small paragraph apart from the
> comment in the example specifically pointing out the value of these
> parentheses - but I can't wrap my head around it. Any help
> appreciated!
>
> Sincerely, Johan
>