pf.conf and cable modem

RW fbsd06 at
Wed Feb 28 18:02:19 UTC 2007

On Wed, 28 Feb 2007 12:44:21 -0500
alex at wrote:

> Quoting RW <fbsd06 at>:

> > When I used DHCP with PF, I found that it just worked without any
> > rules at all.
> That's been my experience as well (admittedly on OpenBSD, but it's 
> basically the same PF). Remember, your NIC's initialization sequence, 
> which is where the DHCP request will come, happens before PF is 
> enabled, so you're essentially at a "pass all" sort of a state when
> the request happens.
> The one thing to keep in mind is that if you're doing, say, NAT for 
> some clients behind the box, you can use a rule like this to deal
> with any changes in your dynamic IP 

Not in my experience.

I was using a half-bridge modem that had a 30 second lease time, which
was definitely renewing. It would also give me a private address when
PPPoA went down, and I saw that happen too. 

I added-in some early static rules to log all the DHCP packets. IIRC I
never saw any of the lease renewal packets, just some broadcast
packets. I asked in this list about it but never got a reply.

I suspect that either DHCP sees the packets directly in some way, or PF
has some special handling for DHCP. In either case it would make sense
for PF rules to see the broadcasts, since they might need to be

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