[Cake] [Cerowrt-devel] conntrack and ipv6

[moeller0]

Hi Dave,


> On Jul 2, 2016, at 14:47 , Dave Täht <dave at taht.net> wrote:
> 
> It is generally my hope that ipv6 nat will not be widely deployed.

	I checked a few RFCs and both NAT66 (https://tools.ietf.org/html/draft-mrw-behave-nat66-02) or NPTv6 (https://tools.ietf.org/html/rfc6296) only seem to change the prefix-part while maintaining the last 64 bit of IPv6 addresses so that cake will see different (somewhat) stable IPv6 addresses (probably just as stable as IPv6 privacy addresses can be), so internal-IP fairness should not require conntrack at all. They also thankfully leave the port numbers alone, maening that neither udp nor tcp headers typically need to be touched, nice…
        Now, if someone should come up with NATv6/128 that hides all internal addresses behind a single /128 and does the old port remapping song and dance, I believe that person should be entitled to keep all the pieces…


> 
> Firewalls will be stateful instead, and thus there would be no need to
> access the conntrack information for ipv6 in cake.
> 
> I'm not sure, however, to
> what extent ipv6 conntrack is in openwrt today, certainly udp and tcp,
> "in" is essentially blocked by default, and needs to be triggered by an
> outgoing message. Similarly I'm unfamiliar with the state of ipv6 upnp
> and pcp support in openwrt or client applications at present.
> 
> 
> On 6/30/16 10:33 AM, Kevin Darbyshire-Bryant wrote:
>> 
>> 
>> On 02/06/16 13:29, Jonathan Morton wrote:
>>>> On 2 Jun, 2016, at 14:09, Kevin Darbyshire-Bryant
>>>> <kevin at darbyshire-bryant.me.uk> wrote:
>>>> 
>>>> Cake uses the flow dissector API to do flow hashing...including per
>>>> host flows for dual/triple isolation.  The unfortunate bit is that
>>>> the qdisc inevitably gets placed after packets have been NATed on
>>>> egress and before they've been de-NATed on ingress.
>>>> 
>>>> When mentioned before Johnathan said "flow dissector ideally needs to
>>>> be tweaked to do this" or words to that effect.
>>>> 
>>>> I'd like to progress that idea...the thought of me kernel programming
>>>> should horrify everyone but really I'm asking for help in being
>>>> pointed in the right direction to ask for help...and go from there :-)
>>> I believe Linux does NAT using a “connection tracker” subsystem.  That
>>> would contain the necessary data for resolving NAT equivalents.  I
>>> don’t know how easy it is to query in a qdisc context, though.
>> Imagine my joy of discovering http://fatooh.org/esfq-2.6/  - someone has
>> already bl**dy done it....and I found it lurking in LEDE as part of a
>> patch.
>> 
>> So there relevant bits are something of the order:
>> 
>> 
>> +#ifdef CONFIG_NET_SCH_ESFQ_NFCT
>> +       enum ip_conntrack_info ctinfo;
>> +       struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
>> +#endif
>> 
>> +#ifdef CONFIG_NET_SCH_ESFQ_NFCT
>> +       /* defaults if there is no conntrack info */
>> +       info.ctorigsrc = info.src;
>> +       info.ctorigdst = info.dst;
>> +       info.ctreplsrc = info.dst;
>> +       info.ctrepldst = info.src;
>> +       /* collect conntrack info */
>> +       if (ct && ct != &nf_conntrack_untracked) {
>> +               if (skb->protocol == __constant_htons(ETH_P_IP)) {
>> +                       info.ctorigsrc =
>> ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip;
>> +                       info.ctorigdst =
>> ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u3.ip;
>> +                       info.ctreplsrc =
>> ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip;
>> +                       info.ctrepldst =
>> ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip;
>> +               }
>> +               else if (skb->protocol == __constant_htons(ETH_P_IPV6)) {
>> +                       /* Again, hash ipv6 addresses into a single u32. */
>> +                       info.ctorigsrc =
>> jhash2(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip6, 4,
>> q->perturbation);
>> +                       info.ctorigdst =
>> jhash2(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u3.ip6, 4,
>> q->perturbation);
>> +                       info.ctreplsrc =
>> jhash2(ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip6, 4,
>> q->perturbation);
>> +                       info.ctrepldst =
>> jhash2(ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip6, 4,
>> q->perturbation);
>> +               }
>> +
>> +       }
>> +#endif
>> 
>> I'd rip out the IPv6 conntrack stuff as I'm much more concerned by
>> handling IPv4 NAT.  And I'm not sure how to get it into cake's host
>> handling yet but....
>> 
>> I can feel an experiment and hackery coming on later today :-)
>> 
>> Am overjoyed!
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