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Date:      Sat, 1 May 2021 10:37:42 -0400
From:      Paul Mather <paul@gromit.dlib.vt.edu>
To:        freebsd-questions@freebsd.org
Subject:   Re: PF with IPv6
Message-ID:  <90DCF979-C3AE-4775-BE39-DB3F455F7D4E@gromit.dlib.vt.edu>
In-Reply-To: <mailman.73.1619870406.98508.freebsd-questions@freebsd.org>
References:  <mailman.73.1619870406.98508.freebsd-questions@freebsd.org>

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On Fri, 30 Apr 2021 21:20:48 -0700, Doug Hardie <bc979@lafn.org =
<mailto:bc979@lafn.org>> wrote:

> Message: 3
> Date: Fri, 30 Apr 2021 21:20:48 -0700
> From: Doug Hardie <bc979@lafn.org <mailto:bc979@lafn.org>>
> To: FreeBSD Questions <freebsd-questions@freebsd.org =
<mailto:freebsd-questions@freebsd.org>>
> Subject: PF with IPv6
> Message-ID: <2CD4806C-F1A4-4DDE-8C2F-2B0A08EA2A18@sermon-archive.info =
<mailto:2CD4806C-F1A4-4DDE-8C2F-2B0A08EA2A18@sermon-archive.info>>
> Content-Type: text/plain;	charset=3Dus-ascii
>=20
> FreeBSD 13-RELEASE.  I have a small test network setup and tried to =
block all IPv6 except those addressed to a specific address.  =
/etc/pf.conf contained:
>=20
> ext_if =3D "bge0"
> LAN3 =3D "2001:1000:0:3000::/64"
> pass in quick log on $ext_if proto ipv6 from $LAN3 to $LAN3
> block in log on $ext_if proto ipv6 from any to any
>=20
> Nothing got blocked.  pftop showed all zeros for both rules.  I then =
added at the end:
>=20
> pass in quick log on $ext_if proto icmp6 from $LAN3 to $LAN3
> block in log on $ext_if proto icmp6 from any to any
>=20
> A lot of stuff got blocked.  The log shows many entries like:
>=20
> 15:59:41.597632 rule 3/0(match): block in on bge0: (hlim 1, =
next-header Options (0) payload length: 32) fe80::120c:6bff:fe5d:4404 > =
ff02::1: HBH (rtalert: 0x0000) (pad1)(pad1) ICMP6, multicast listener =
query
> 	0x0000:  6000 0000 0020 0001 fe80 0000 0000 0000  =
`...............
> 	0x0010:  120c 6bff fe5d 4404 ff02 0000 0000 0000  =
..k..]D.........
> 	0x0020:  0000 0000 0000 0001 3a00 0502 0000 0000  =
........:.......
> 	0x0030:  8200 98aa                                ....
>=20
> Rule 3 is the block for ICMP6, but those are clearly IP6 packets that =
should have been blocked by rule 1. Is there a problem with IPv6 and pf?


It's not clear to me precisely what you are trying to achieve.  The =
"proto" keyword in PF rules refers to protocols in /etc/protocols.  Your =
rules appear to be targeting the specific case of filtering IPv6 =
encapsulated in IPv4.  I don't believe that is what you intend.

The more standard way in PF to block IPv6 vs IPv4 traffic is to use =
"inet" (IPv4) or "inet6" (IPv6) to target IPv4 or IPv6 packets.

Note, the last rule you added that you say did start blocking things is =
more typical of rules to block ICMP6.  Because you omit "inet" or =
"inet6" on the rule it will be applied to both IPv4 and IPv6 packets.  =
But, the "proto icmp6" part is specifically targeting ICMP6.

So, to summarise, use "inet" and "inet6" to select IPv4 and IPv6 and =
"proto" to select the protocol you want to target (e.g., "tcp", "udp", =
"icmp", "icmp6", etc.).  E.g., "pass in log quick on $ext_if inet6 from =
..." to allow all IPv6 for the rule, or ""pass in log quick on $ext_if =
inet6 proto tcp from ..." to allow only IPv6 TCP traffic, etc.

Cheers,

Paul.=



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