RE: IPv6 only host NAT64 requirements?

<mohamed.boucadair@orange.com> Fri, 17 November 2017 08:47 UTC

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From: <mohamed.boucadair@orange.com>
To: Jen Linkova <furry13@gmail.com>
CC: Ole Troan <otroan@employees.org>, 6man WG <ipv6@ietf.org>, Mark Andrews <marka@isc.org>
Subject: RE: IPv6 only host NAT64 requirements?
Thread-Topic: IPv6 only host NAT64 requirements?
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Date: Fri, 17 Nov 2017 08:47:44 +0000
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Hi Jen, 

Please see inline. 

Cheers,
Med

> -----Message d'origine-----
> De : Jen Linkova [mailto:furry13@gmail.com]
> Envoyé : vendredi 17 novembre 2017 09:31
> À : BOUCADAIR Mohamed IMT/OLN
> Cc : Ole Troan; 6man WG; Mark Andrews
> Objet : Re: IPv6 only host NAT64 requirements?
> 
> On Thu, Nov 16, 2017 at 12:35 AM,  <mohamed.boucadair@orange.com>; wrote:
> >> IMHO the optimal solution is:
> >> - the network SHOULD provide a host with NAT64 prefix information in
> >> RA (I do not believe that information needs to be duplicated in DHCP
> >> at all);
> >
> > [Med] Please check: https://tools.ietf.org/html/rfc7051#section-5.7.3
> 
> Thanks for pointing this out. To be honest I disagree with what that
> section says.

[Med] I also disagree with many of the points in RFC7051, but that is the document which reflects the IETF consensus on learning prefix64s. 

We had many opportunities in the past to ignore the recommendations in RFC7051, but we didn't. For example, RFC8115 says the following: 

==
   Note that it was tempting to define three distinct DHCPv6 options,
   but that approach was not adopted because it has a side effect: the
   specification of a DHCPv6 option that could be used to discover
   unicast Prefix64s in environments where multicast is not enabled.
   Such a side effect conflicts with the recommendation to support the
   Well-Known DNS Name heuristic discovery-based method for unicast-only
   environments (Section 6 of [RFC7051]).
==

> I'm trying to refrain from participating  'SLAAC vs DHCPv6' so I will
> not mention all those issues with multihoming for example but....
> If you are saying that the prefix should not be distributed via RAs
> because it needs to be configured on routers, then what about DNS
> servers and SLAAC prefixes themselves?
> There are SLAAC-only networks out there while RFC7934 does not
> recommend DHCPv6 as the only way to configure clients.
> So between those two RA does look like a better way.

[Med] It is evident that RA-based approach may be a good candidate for some deployments. Others may argue that another solution is appropriate for their deployment, and so on. 

> 
> > Things may get complex if multiple NSPs are used for load-balancing or
> if destination based NAT64s are deployed. A list of issues is elaborated
> in https://tools.ietf.org/html/rfc7225#section-3.1
> 
> It's more like v6ops question but I'm really curious if multiple
> prefixes scenario is real.
> RA option might contain multiple prefixes anyway.

[Med] Indeed. It is already ACKed in 7051: 

   Note: If the RA would include multiple NSPs, Issue #5 could be solved
   as well, but only if nodes as a group would select different NSPs,
   hence supporting load balancing.  As this is not clear, this item is
   not yet listed under PROs or CONs.

> 
> >> >> On 15 Nov 2017, at 08:06, Mark Andrews <marka@isc.org>; wrote:
> >> >>
> >> >>
> >> >>> On 15 Nov 2017, at 3:40 am, Lorenzo Colitti <lorenzo@google.com>;
> >> wrote:
> >> >>>
> >> >>> On Tue, Nov 14, 2017 at 6:46 AM, Mark Andrews <marka@isc.org>;
> wrote:
> >> >>> Is there any reason to run DNS64 at all these days?  ipv4only.arpa
> can
> >> be a preconfigured
> >> >>> zone which allows CLAT to get its mapping.  All the phones have
> CLAT
> >> support.
> >> >>>
> >> >>> That's an interesting idea. It would work in theory, but such a
> >> network would completely break devices that don't support 464xlat. That
> >> gives up one of the major advantages of NAT64/DNS64, which is that it's
> a
> >> 90% solution even just by itself - yes, IPv4-only applications and
> address
> >> literals exist, but most simple client/server applications Just Work
> >> behind it.
> >> >>
> >> >> And that 90% “solution” has lots of down sides.  It basically
> requires
> >> EVERY DNS VALIDATOR ON
> >> >> THE PLANET TO SUPPORT DNS64 JUST IN CASE IT IS USED BEHIND A DNS64
> >> SERVER.
> >> >>
> >> >> DNS64/NAT64 was presented as NOT REQUIRING node changes when first
> >> mooted.  It keeps on
> >> >> requiring more and more highly invasive node changes to support.  It
> >> was from the very beginning
> >> >> bad engineering.   To get IPv4 as a service some node changes are
> >> required.  Lets make sure they
> >> >> are MINIMAL ones.
> >> >>
> >> >> Just for the record DNSSEC validators need to send BOTH CD=0 and
> CD=1
> >> queries to get answers
> >> >> though a upstream VALIDATING server which includes a VALIDATING
> DNS64
> >> server as CD=0 and
> >> >> CD=1 address different DNSSEC threats.  I tried very hard to point
> that
> >> out when RFC 6147 was
> >> >> being written but the working group decide that CD indicated whether
> >> the client was validating or
> >> >> not.  There is NO SUCH INDICATION in a DNS message.
> >> >>
> >> >>  If a query arrives at a vDNS64 device with the "Checking Disabled"
> >> >>   (CD) bit set, it is an indication that the querying agent wants
> all
> >> >>   the validation data so it can do checking itself.  By local
> policy,
> >> >>   vDNS64 could still validate, but it must return all data to the
> >> >>   querying agent anyway.
> >> >>
> >> >> CD=0 queries causes the upstream validating servers to reject
> incoming
> >> spoofed answers
> >> >> or stale answers (this is a common operational problem).
> >> >>
> >> >> CD=1 queries allow the validation to succeed when the upstream
> >> validator has a bad trust
> >> >> anchor or a bad clock which is rejecting legitimate answers.
> >> >>
> >> >> A validating client can’t just send CD=1 queries as the upstream
> >> validator doesn’t kick in.
> >> >> The upstream validator can lock onto a stale answer source.  It
> needs
> >> to send CD=0 queries
> >> >> on validation failure to force the upstream validator to try
> multiple
> >> sources.
> >> >>
> >> >> A validating client can’t just send CD=0.  It needs to send CD=1 on
> >> SERVFAIL in case the
> >> >> upstream validator has a bad trust anchor (likely with the upcoming
> >> root KSK roll) or has
> >> >> a bad clock (these usually get fixed fast).
> >> >>
> >> >> Now to get a answer from a signed zone with servers with stale
> answers
> >> a validatiing DNS64 client
> >> >> needs to send:
> >> >>
> >> >> a) send CD=1 and validation failure send CD=0 then on AAAA
> validation
> >> failure send CD=1 and
> >> >>    hope the TTL was not 0 and that is not cachable and there is no
> >> assurance that you won’t get
> >> >>    a answer from a stale source.
> >> >>
> >> >>       or
> >> >>
> >> >> b) send CD=0 and on validation failure of the AAAA send CD=1 and
> hope
> >> the TTL was not 0 as
> >> >>    that is not cachable and there is no assurance that you won’t get
> a
> >> answer from a stale source.
> >> >>
> >> >> TTL=0 answers exist.
> >> >>
> >> >> Note none of this is documented in a RFC.  You have to understand
> how
> >> both DNSSEC and DNS64 work to
> >> >> realise this.
> >> >>
> >> >> IPV4ONLY.ARPA is currently has a secure delegation which breaks
> prefix
> >> discover for DNS VALIDATORS.
> >> >> Note “ad” is set in the flags.  Yes, I’ve submitted a errata.  Yes,
> >> I’ve opened a ticket to get it fixed but
> >> >> based on past experience that could take months if it happens at
> all.
> >> You will note that the recursive
> >> >> server is running on the loopback interface so all DNS answers are
> >> being validated here.
> >> >>
> >> >> [rock:bind9/bin/named] marka% dig IPV4ONLY.ARPA
> >> >> ;; BADCOOKIE, retrying.
> >> >>
> >> >> ; <<>> DiG 9.12.0b2+hotspot+add-prefetch+marka <<>> IPV4ONLY.ARPA
> >> >> ;; global options: +cmd
> >> >> ;; Got answer:
> >> >> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8504
> >> >> ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0,
> ADDITIONAL: 1
> >> >>
> >> >> ;; OPT PSEUDOSECTION:
> >> >> ; EDNS: version: 0, flags:; udp: 4096
> >> >> ; COOKIE: 7dbf8beb79be47a09eb5313d5a0b776f4fae3aa6931d9583 (good)
> >> >> ;; QUESTION SECTION:
> >> >> ;IPV4ONLY.ARPA.                       IN      A
> >> >>
> >> >> ;; ANSWER SECTION:
> >> >> ipv4only.arpa.                26574   IN      A       192.0.0.171
> >> >> ipv4only.arpa.                26574   IN      A       192.0.0.170
> >> >>
> >> >> ;; Query time: 0 msec
> >> >> ;; SERVER: 127.0.0.1#53(127.0.0.1)
> >> >> ;; WHEN: Wed Nov 15 10:08:31 AEDT 2017
> >> >> ;; MSG SIZE  rcvd: 115
> >> >>
> >> >> [rock:bind9/bin/named] marka%
> >> >>
> >> >>> It's not true that all phones have clat support. Notably, Apple not
> >> only does not support it but appears ideologically opposed to it on the
> >> grounds that it does not have a good exit strategy (because it makes it
> >> possible to run IPv4-only apps forever).
> >> >>
> >> >>
> >> >> --
> >> >> Mark Andrews, ISC
> >> >> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> >> >> PHONE: +61 2 9871 4742              INTERNET: marka@isc.org
> >> >>
> >> >> --------------------------------------------------------------------
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> >> >> --------------------------------------------------------------------
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> >>
> >>
> >>
> >> --
> >> SY, Jen Linkova aka Furry
> >>
> >> --------------------------------------------------------------------
> >> IETF IPv6 working group mailing list
> >> ipv6@ietf.org
> >> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
> >> --------------------------------------------------------------------
> 
> 
> 
> --
> SY, Jen Linkova aka Furry