Re: IPv6 only host NAT64 requirements?

Ole Troan <otroan@employees.org> Fri, 17 November 2017 09:19 UTC

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From: Ole Troan <otroan@employees.org>
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Subject: Re: IPv6 only host NAT64 requirements?
Date: Fri, 17 Nov 2017 17:19:46 +0800
In-Reply-To: <787AE7BB302AE849A7480A190F8B93300A07C625@OPEXCLILMA3.corporate.adroot.infra.ftgroup>
Cc: Jen Linkova <furry13@gmail.com>, 6man WG <ipv6@ietf.org>, Mark Andrews <marka@isc.org>
To: Mohamed Boucadair <mohamed.boucadair@orange.com>
References: <m1eEGbJ-0000EhC@stereo.hq.phicoh.net> <D43E103C-27B8-48CF-B801-ACCF9B42533E@employees.org> <m1eEHPS-0000FyC@stereo.hq.phicoh.net> <59B0BEC0-D791-4D75-906C-84C5E423291B@employees.org> <m1eEIGX-0000FjC@stereo.hq.phicoh.net> <73231F8D-498E-4C77-8DA8-044365368FC9@isc.org> <CAKD1Yr1aFwF_qZVp5HbRbKzcOGqn==MRe_ewaA8Qc8t3+CVu_Q@mail.gmail.com> <44A862B7-7182-4B3A-B46E-73065FC4D852@isc.org> <D42D8D7A-6D19-4862-9BB3-4913058A83B6@employees.org> <CAFU7BARCLq9eznccEtkdnKPAtKNT7Mf1bW0uZByPvxtiSrv6EQ@mail.gmail.com> <787AE7BB302AE849A7480A190F8B93300A07AD68@OPEXCLILMA3.corporate.adroot.infra.ftgroup> <CAFU7BARoXgodiTJfTGc1dUfQ8-ER_r8UOE1c3h-+G0KTeCgBew@mail.gmail.com> <787AE7BB302AE849A7480A190F8B93300A07C625@OPEXCLILMA3.corporate.adroot.infra.ftgroup>
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Med,

Thanks for all the references. Seems like most bases have been covered here. ;-)

For the IETF NAT64 IMHO I need:
 - No dependency on DNS64. Want to use recursive resolver I trust plus local validating resolver.
 - Not depend on the success of PCP for NAT64 prefix discovery
 - If the host couldn't learn the NAT64 prefix any other way, I suppose it could throw an ICMP echo towards
   64:ff9b::127.0.0.1 (or perhaps just 64:ff9b::)

But I also see there being different deployment options here.
Btw, for multiple NSPs, couldn't you partly solve that by injecting more specifics into routing?

Cheers,
Ole


> On 17 Nov 2017, at 16:47, <mohamed.boucadair@orange.com>; <mohamed.boucadair@orange.com>; wrote:
> 
> 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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>>>>>> ipv6@ietf.org
>>>>>> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
>>>>>> --------------------------------------------------------------------
>>>>> 
>>>>> 
>>>>> --------------------------------------------------------------------
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>>>>> ipv6@ietf.org
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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