Re: IPv6 only host NAT64 requirements?

Fred Baker <fredbaker.ietf@gmail.com> Fri, 17 November 2017 08:47 UTC

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Subject: Re: IPv6 only host NAT64 requirements?
From: Fred Baker <fredbaker.ietf@gmail.com>
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Date: Fri, 17 Nov 2017 16:47:02 +0800
Cc: Mohamed Boucadair <mohamed.boucadair@orange.com>, 6man WG <ipv6@ietf.org>, Mark Andrews <marka@isc.org>
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To: Jen Linkova <furry13@gmail.com>
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To be very honest, situations like Tore’s have always made me question the wisdom of a special prefix for IPv4/IPv6 NAT. One is communicating with a peer at an IPv6 address. One got the address because the initiating SYN-or-whatever came from it, or the address was provided in DNS. Tomorrow, with any luck, it will be a native address; today, it is a /96 embedded in a /64, one of many /64s in the network.

Why should I know or care that the path to the peer has a NAT in it? Yes, there are some end to end session assumptions that fail. No matter what I do, they will fail. I at least have as good connectivity as I would have in an IPv4 network.

Sent using a machine that autocorrects in interesting ways...

> On Nov 17, 2017, at 4:38 PM, Fred Baker <fredbaker.ietf@gmail.com>; wrote:
> 
> Tore Anderson has a multiple prefix installation.
> 
> Sent using a machine that autocorrects in interesting ways...
> 
>> On Nov 17, 2017, at 4:30 PM, Jen Linkova <furry13@gmail.com>; wrote:
>> 
>> 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.
>> 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.
>> 
>>> 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.
>> 
>>>>>> 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
>>>> 
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>> 
>> 
>> 
>> -- 
>> SY, Jen Linkova aka Furry
>> 
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