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Date:      Sun, 2 May 2021 17:40:26 -0700
From:      Doug Hardie <bc979@lafn.org>
To:        Paul Mather <paul@gromit.dlib.vt.edu>
Cc:        FreeBSD Questions <freebsd-questions@freebsd.org>
Subject:   Re: PF with IPv6
Message-ID:  <DB4F0B73-57B0-4189-836A-318966FA03A7@sermon-archive.info>
In-Reply-To: <90DCF979-C3AE-4775-BE39-DB3F455F7D4E@gromit.dlib.vt.edu>
References:  <mailman.73.1619870406.98508.freebsd-questions@freebsd.org> <90DCF979-C3AE-4775-BE39-DB3F455F7D4E@gromit.dlib.vt.edu>

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> On 1 May 2021, at 07:37, Paul Mather <paul@gromit.dlib.vt.edu> wrote:
>=20
> On Fri, 30 Apr 2021 21:20:48 -0700, Doug Hardie <bc979@lafn.org =
<mailto:bc979@lafn.org>> wrote:
>=20
>> 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?
>=20
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> 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.

First, it appeared to me that since ipv6 is listed in /etc/protocols, =
that it could be used as a protocol.  However, after reading the man =
page again, I see where it wants family, not protocol.  With that change =
it does work.

What I was trying to do was to simulate a multi LAN configuration using =
only one physical LAN.  This is quite easy to do with IPv4, but even =
with a bunch of pf rules, there are issues with the multicast packets.  =
Hosts should only listen to packets addressed to their virtual LAN but =
multicast packets are not identifiable by which virtual LAN they were =
sent to.  So I ended up adding a bunch of switches and building the =
complete multi LAN configuration.

Thanks,
--Doug





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