Filtering specific devices, using mac-based Policy Filtering



  • Hello,

    IMHO good IPV6-firewalling is only possible with the addition of MAC based filtering. See my thread “FW-rules related to an specific "IPV6-device". So I am looking for options to archive that.

    Regrettable pfSense does not support mac-based firewall rules, however pfSense does support “Policy Based Filtering” (Filter rules advanced).

    Policy Based routing is based on the idea to Tag an ethernet frame in rule-1 and to use that tag in rule-2.

    And … the trick is ... that it should be possible to set that tag on ethernet level, based on source mac of one of your devices in one of your own directly pfSense attached (v)lans.

    Any one knowing how to do that in pfSense?
    Any one experiences with that?

    Of course it would be a terrific idea if it could be implemented in the Gui ☺ ☺

    Louis
    Also see e.g. http://www.openbsd.org/faq/pf/tagging.html


  • Rebel Alliance Developer Netgate

    pf does not see L2 info, and the tags have to be set by and read by pf, so that isn't possible.

    Also, IPv6 filtering by MAC is just as inaccurate as IPv4. IPv6 hosts are identified by their DUID, not MAC. But the DUID is not visible in packets.



  • @jimp

    No DUID should never/not be used. It is not stable. The MAC-address is(!) appart from spoofing.

    There are a significant number of Firewall out there which do support MAC-filtering. For exactly the indicated problem (you can use it in a combined IPV4/IPV6-rule as well).

    Yep, I know that pf does not support mac filtering, however as far as my knowledge goes, tags are stored in the ethernet frame and pf can read the frames. It even does already do so ☺ in case of the allready pfSense supported policy based routing.

    So if there is a functionality in layer-2 which set that tag before the frame arrives at pf, pf should be able to deal with it.

    As example see the link in the first post (not the best one, but it gives some idea).

    Louis


  • Rebel Alliance Developer Netgate

    You are wrong. The DUID is stable for every interface on a host since it identifies the host itself uniquely. MAC addresses and IAID values vary by interface. A host will have the same DUID no matter what interface it uses.

    MAC address randomization for privacy is also a thing. Evading MAC address blocks is trivial.


  • Rebel Alliance Developer Netgate



  • @jimp

    I will read the documentation carefully, but I have some doubts about DUID stabiltiy.
    ...... and I never heard about DUID filtering .....

    I understand that the DUID is created by the node/computer/IoT device itself. I believe that there are 3 types of DUID:

    DUID-LLT = link layer address plus timestamp
    Vender assigned unique ID based on manufacturer
    Link layer address
    

    A probem with macs could be, depending on use case, that you can assign multiple IP to one MAC. So you would block every thing, that could be an advantage or a disadvantage.

    As said I will read the docs.


  • Rebel Alliance Developer Netgate

    You wouldn't filter by DUID, necessarily, but you would assign static addresses based on the DUID and filter on the statics. Naturally someone could change their address to static and get around that, too, but it's as good as other methods in that regard, plus has the benefit of catching wired and wireless versions of the same client. Of course that doesn't help SLAAC or link-local. IPv6 has done a lot to enable user privacy, but it's a nightmare for network admins if you need to corral malicious users.



  • @jimp,

    My first impression is that that only helps for incoming and not for outgoing (as seen from the "device" to filter.

    If my impression is correct ..... , it is not / far from "an optimal" solution

    Louis

    Note that an average IP-device has lots of IP-addresses …….
    IPv6 Address. . . . . . . . . . . : 2001🔤:axyz:1cd::33(Preferred)
    IPv6 Address. . . . . . . . . . . : 2001🔤:axyz:1cd::f34b(Preferred)
    IPv6 Address. . . . . . . . . . . : 2001🔤:axyz:1cd:a827:d6e7:38b0:7beb(Preferred)
    Temporary IPv6 Address. . . . . . : 2001🔤:axyz:1cd:a02f:8726:d593:c682(Preferred)
    Link-local IPv6 Address . . . . . : fe80::a827:d6e7:38b0:7beb%3(Preferred)



  • @jimp said in Filtering specific devices, using mac-based Policy Filtering:

    You are wrong. The DUID is stable for every interface on a host since it identifies the host itself uniquely. MAC addresses and IAID values vary by interface. A host will have the same DUID no matter what interface it uses.
    MAC address randomization for privacy is also a thing.

    I thought the DUID was for use with DHCPv6 and would not be in every packet, as required for a firewall. Also, while I am aware of MAC spoofing, I haven't heard of MAC randomization. IPv6 privacy addresses use random numbers though.



  • @jimp said in Filtering specific devices, using mac-based Policy Filtering:

    You wouldn't filter by DUID, necessarily, but you would assign static addresses based on the DUID and filter on the statics.

    That would require using DHCPv6 on the LAN side, where SLAAC is often used. With SLAAC, you can have up to 7 privacy addresses and you get a fresh one every day.



  • @louis2 said in Filtering specific devices, using mac-based Policy Filtering:

    that you can assign multiple IP to one MAC.

    That's entirely normal with IPv6. With SLAAC, GUA, ULA and link local addresses, I have up to 17 different IPv6 addresses for each MAC.



  • @JKnott,

    Yep, of course all you wrote is true ! , thats exactly the reason I advocate for MAC-filtering !
    ☺

    Louis


  • Rebel Alliance Developer Netgate

    Right, you don't see the DUID in a packet, but it is used to uniquely identify a host. MAC addresses are no longer considered a reliable unique host identifier. They are used in some places to help form certain kinds of automatic addresses, but they can be changed/randomized/etc. See my link to RFC 7844 above which has info on it (though some is still theoretical)



  • @jimp

    I need something which can be used for incomming and for outgoing and which is stable appart from spoofing!

    Louis



  • @jimp

    Once again, you don't see DUID on the wire, except with DHCPv6. This means you cannot filter on it and would require DHCPv6 to assign addresses. That brings us to the problem where (for some idiotic reason) Android devices can't use DHCPv6.


  • Rebel Alliance Developer Netgate

    And pf can't filter based on MACs, so that's a dead end and not a possibility.

    Also you can't do MAC filtering on traffic inbound from the Internet to local hosts so that doesn't help you in that direction anyhow.

    "stable apart from spoofing" is meaningless since unless you isolate and filter clients properly at L1/L2 (read: switches and APs) everything can be spoofed.



  • @jimp

    I built my first firewall with Slackware Linux and IPChains, later SUSE and IPTables. I don't remember about IPChains, but IPTables could definitely filter on MAC addresses. The reason I switched to pfSense was because Linux didn't work with DHCPv6-PD.

    Also you can't do MAC filtering on traffic inbound from the Internet to local hosts so that doesn't help you in that direction anyhow.

    Yep. I was at a Linux meeting a few years ago, where I had to correct the presenter on that point.



  • In a manner of speaking, widespread adoption of IPv6 in the future is going to just about send firewalls the way of the horse and buggy ... ☺. There is, of course, some hyperbole in that statment, but ...

    Individual client security/monitoring/policing will get way harder than today since a given client can have a ton of addresses. Sure you will still be able to do subnet-level stuff, but individual host stuff gets orders of magnitude harder.



  • @jimp

    If I have a computer or an IoT device I want to limit in its behavior, it will be very unlikely that it is spoofed.

    And if I was afraid of that, I could try to detect that!

    Of course you can only filter on MACs related to my own network, but with that limitation, I do not see a reason why I could filter based on starting mac (in vlan-1) or on destination mac (in vlan-2).

    Of course given a situation, where level-2-tags could be read by pf (I think vlanid is one of them)

    So I would not be surprised if pf could do that! It is almost identical to policy based routing. But of course that should be checked with a high level expert.

    I know that it is possible on OpenBSD and elsewhere, but of course that does not necessary that it is also possible on freebsd/pf combination.

    Louis



  • @louis2

    Of course, this is a FreeBSD problem, not pfSense, due to the pf filtering that FreeBSD uses. If it used IPTables, it wouldn't be an issue. So, this problem really should go back to the FreeBSD folks.



  • Just to indicate a potential solution direction,

    A potential solution does in volve "Tagging of Ethernet Frames"

    Tagging can be performed at the ethernet level if the machine doing the tagging/filtering is also acting as a bridge(4). By creating bridge(4) filter rules that use the tag keyword, PF can be made to filter based on the source or destination MAC address. Bridge(4) rules are created using the ifconfig(8) command. Example:

    step-1: ifconfig bridge0 rule pass in on fxp0 src <mac-address> tag <sometag>
    step-2: And then in pf.conf: pass in on fxp0 tagged <sometag> (policy based rule)

    This direction seems to imply that there must be bridge on ethernet level. That could perhaps significant complicate things ☹

    Louis


  • Rebel Alliance Developer Netgate

    That is not available on FreeBSD. That is an OpenBSD-specific function.



  • @louis2

    Hi
    Unfortunately , as we have already said, PF is not able to work with network packets at the L2 level.
    But the FreeBSD/PF kernel has a very powerful NETGRAPH network subsystem built in. You can use it to configure packet filtering based on the MAC address . This subsystem allows you to intercept traffic before it reaches the network stack of the operating system and analyze it.
    Here is its description
    https://www.freebsd.org/cgi/man.cgi?netgraph(4)

    You will need modules to analyze the ethernet header

    ng_ether + ng_vlan (possibly) + ng_bpf



  • Thanks for the tip,

    I just scanned the doc, will read in more detail later. Perhaps there are some artikels as well on internet.

    However, my first feeling is that it lets say "an advanced acl-filter" on level-2.

    First feeling is that you could perhaps ...:

    • block traffic between A and B (that could be usefull) or
    • allow traffic by passing pfSense (a very bad idea !!)

    And of course with "complexity (and performance)" as price

    What ever, worth reading more ☺

    Louis





  • @louis2

    Since the modules of this subsystem work at the kernel level, it is very high-performance and does not exert a strong load on the system.
    Yes, at first it is difficult to understand , but you can understand it
    The main difficulty is creating a BPF program for filtering packets . The rest is easy .
    for example, to intercept traffic from a device with the MAC address 98:01:a7:8c:eb:89, the program will look like this
    ether[6:4]=0x9801a78c and ether[10:2]=0xeb89
    (000) ld [6]
    (001) jeq #0x9801a78c jt 2 jf 5
    (002) ldh [10]
    (003) jeq #0xeb89 jt 4 jf 5
    (004) ret #262144
    (005) ret #0

    bpf_prog_len=6 bpf_prog=[ { code=32 jt=0 jf=0 k=6 } { code=21 jt=0 jf=3 k=2550245260 } { code=40 jt=0 jf=0 k=10 } { code=21 jt=0 jf=1 k=60297 } { code=6 jt=0 jf=0 k=65535 } { code=6 jt=0 jf=0 k=0 } ]

    Netgraph is managed from the console by the ngctl utility. For automation, you will need to write a script.
    And, most importantly, you must have physical access to the console , because it is very easy to lose access to the firewall



  • I do not know yet however,

    I am not so sure about this package, it seems a package to build a L2-switch or router.

    However that layer has been built by NetGate and apart from my limited knowledge, I absolutely do not want to interfere with their L2-design !!

    Also note that I was not looking for a level-2 filter! If there was not IPV6 with all its "strange addresses" which are undermining firewalls, I would never be advocating MAC-addresses here. But given lack of a decent and stable IPV6-adres, you need that as attribute for level-3 filtering.

    So, I will do some further reading, but my first impression is that this is not an option for the given problem. And in case I am mistaken (I hope), it must be implemented by NetGate in order to keep the system consistent and reliable.

    Louis.



  • @louis2

    This subsystem does not work in conjunction with PF . For example, it works perfectly with ipfw ( it is used by this firewall for deep packet inspection ) .

    Simply using its capabilities , you can filter packets based on the device's mac address, vlanid, and other attributes (ip, tcp/udp packets).

    But, unfortunately, using this subsystem, you can't create tags that PF would understand.


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