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Versions: 00 01                                                         
Network Working Group                                      M. Richardson
Internet-Draft                                                       SSW
Intended status: Informational                         November 14, 2012
Expires: May 18, 2013

             Secret Gardens are Better than Walled Gardens


   This document explains a few use cases where operators would like to
   introduce so-called "walled gardens" into home-networks, including
   distribution of new DNS anchors.  This document proposes an
   alternative solution involving DNS delegations to access controlled
   DNS servers.  The results are much more scalable, and can be deployed
   today, using existing operating systems and existing DNS

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 18, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction: A brief history of split-horizon DNS . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  IPv6 TV  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Corporate VPN  . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Multi-homed to 3G/LTE  . . . . . . . . . . . . . . . . . .  6
   3.  Walled Garden DNS  . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Using Secret-Gardens to accomplish goals . . . . . . . . . . .  8
     4.1.  Example 1: Corporate VPN . . . . . . . . . . . . . . . . .  8
   5.  How does this differ from SERVER-SELECTION?  . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  Other Related Protocols  . . . . . . . . . . . . . . . . . . . 13
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Informative References . . . . . . . . . . . . . . . . . . 16
     10.2. Normative References . . . . . . . . . . . . . . . . . . . 16
   11. Normative references . . . . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18

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1.  Introduction: A brief history of split-horizon DNS

   DNS settings have been a regular concern since the very early 1990s,
   when the first firewalls began to partition the Internet.  In the
   earliest works, Cheswick and Bellovin describe the use of split-DNS
   in an enterprise: all internal machines (including the inside
   interface of the firewall, and possibly machines on the DMZ/
   Service-Network) would use an internal recursive DNS server for
   names, and if the name was external, the internal recursive DNS
   server would ask the world.

   The above split-horizon configuration survives to today, but it has
   become very complicated.  The first complication was remote access
   (VPN) to the enterprise.  For the computer at home to be able access
   things, the internal DNS server had to be used.  Often short internal
   names ("smtp", "web", "wiki","printer") would be used, depending upon
   the fact that all internal machines had the same search path.  As the
   VPN could go on, and off, if it was off, and the end user entered the
   word "wiki" on the browser, instead of going to the internal resource
   (which in IPv4 space, had an RFC1918 address), it would either go to
   an external resource, or cause a search.

   Worse, some computer systems originally needed to be rebooted in
   order to change their DNS settings, as this was really the only way
   to convince all application to flush name to IP address mappings that
   they had cached.

   Particularly gruesome is the case of the contractor or consulting,
   who works at enterprise A, and then visits enterprise B. While on the
   network of Enterprise B (where they may be located for some months),
   in order to do simple things like reach the printer (using the name
   "printer"), they need to use the DNS settings for Enterprise B. But,
   in order to fetch their email, they must have the DNS settings (and
   VPN) for their home base, Enterprise A. There have been regular
   reports in the VPN/Remote Access community of situations where a
   worker needs to have VPNs up with two remote locations, while
   residing at a third.

   The VPN situation is tragic for the technical user, for the non-
   technical user, it is impossible.  For the technical user, typing in
   longer names, setting up multiple search paths, and running a local
   recursive name server are possible.  For the less technical user,
   typing in IP addresses rather than names works as long as HTTP
   Virtual Hosting is not involved (for which the name is important).
   But the degree to which these things occur has been limited in part
   due to the inevitable conflict of RFC1918 addresses, which means,
   that, even if one uses IP addresses, the routing doesn't work.

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   DNSSEC has put a new twist into things: the best way to run DNSSEC is
   to have a secure recursive resolver.  Now, this recursive resolver
   needs to be taught about split-horizon names, to talk to the internal
   name server when it is reachable (and probably to trust it), and to
   talk directly to the Internet when not reachable.  A second problem
   is that the local recursive name server may not always get flushed.
   If a query for "smtp.example.com" should result in the internal mail
   relay when at the office, or connected via VPN, but the same name
   should resolve in the external address when not connected (possibly,
   the same machine with multiple interfaces, but not always), then the
   caching presents a problem.  This problem is acute if one tries to
   run a caching name server on a mobile, multiple-interface devices,
   such as a stock smartphone that has 3G and wifi interfaces, which may
   operate concurrently.

   Some organizations, where there are multiple data centres, and the
   network is distinctly non-convex, have solved the caching problem by
   dispensing with a true split-horizon DNS, and have simply put all
   external names under "example.com", with internal names under
   "internal.example.com".  Whether or not externally made requests for
   foo.internal.example.com are resolved by externally facing
   authoritative name servers is now a security policy question, rather
   than a routing or caching concern.

   There have been further abuses of split-horizon DNS.  One of these is
   by hotels and other places with "captive portals".  In order to
   authenticate the user using a web interface, they must make the
   portal visible to the user.  This involves making the user "captive":
   no packets may leave the local network until the user has
   sufficiently authenticated (possibly, involving a financial
   transaction).  Some captive portals have decided that they will
   intercept all DNS requests, and no matter what the user asks for,
   they will answer with their own IP.  This can fail for three reasons:
   1) the user does not use the DNS servers provided, instead uses their
   own (perhaps intending to be reached through a VPN) or or the root
   name servers directly (perhaps in order to do DNSSEC), 2) the names
   used in the web interfaces are unqualified ones, and the user has not
   accepted the search path from the DHCP offer (ref: some BCP on this),
   3) even if all of this goes well, the user's browser has now cached
   an incorrect mapping for the desired web site.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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2.  Use Cases

   This section lists a few use cases which homenet believes are within
   scope.  Only the business goals are listed of the use cases.

2.1.  IPv6 TV

   [SERVER-SELECTION] Section 3.1 "CPU Deployment Scenario" describes a
   similar situation to the IPv6 TV below.

   A seperate internet connection is provided by the IP TV provider.
   This can be on a seperate physical wire, or a seperate logical wire.
   Historically, only the TV set itself is placed on this network, the
   home owner may be unaware that the wires are other than analog cable
   TV wires.

   The TV set does DNS lookups for the content servers, and is expected
   to receive answers that are within the IP TV provider's network.  The
   TV set can access the provider's servers as long as it originates
   connections from the IPv6 prefix that the IP TV provider provided.

   The provider does not publish the addresses of the servers
   publically, and does not want to.  Even if the servers can be
   accessed from the Internet by IP address, they will not serve any TV
   content that way.  It is more likely that the content servers are
   completely inaccessible from the Internet via firewall rules and/or
   routing horizons.

2.2.  Corporate VPN

   [SERVER-SELECTION] Section 3.2 "Cellular Network Scenario" provides
   more details.

   The corporate VPN use case involves an employee of an enterprise
   connecting to the enterprise's network via an IP over IP tunnel.
   IPsec is a typical technology, and there are various kinds of SSL
   VPNs, but this use case concerns itself with scenarios where IPv6
   pakets will be routed through the tunnel.  (Some SSL VPNs provide
   TCP, usually HTTP-only services.  They are not relevant)

   As described in the introduction, the Corporate VPN is almost the
   original walled garden: there is a seperate routing domain (RFC1918
   in IPv4, End-User Assigned IPv6, Non-Connected Network or ULA for
   IPv6), and there is an addition a desire to have an island of DNS.

   Some corporate VPNs have a policy that all traffic from the
   employees' computing device must go through the tunnel, even traffic
   not addressed to the Enterprise.  (That is, the default route on the

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   laptop must point through the tunnel.  A host route for the VPN
   tunnel end point is usually created to permit the encapsulated
   traffic to travel, or another kind of source-address sensitive policy
   route is used to create multiple routing tables).  These types of
   VPNs are sometimes called an extruded IP VPN: if the enterprise'
   network is thought of as a fungible sponge, then the laptop user at
   home as an IP address, from the corporate cloud/sponge, extruded,
   rather like a sea urchin (??) extends a pseudopod.

   It is not unusual for the networks of enterprises to grow to be very
   complex: multiple sites with multiple (sometimes overlapping IPv4
   RFC1918) address spaces.  With IPv6, enterprises are likely to have
   fewer blocks of addresses, and none will overlap, but due to
   acquisitions the number of blocks will still be greater than one.

   Frequent teleworkers often have an entire home office connected to
   the enterprise network.  This can include a selection of desktop
   computers, laptops, tablets, and smartphones (on wifi).  The home
   office network might have several subnets (at least one wired and one
   wireless).  These teleworkers usually have a VPN router as their home
   gateway, and often these devices are controlled by the Enterprise IT.
   Just the same, access to the rest of the homenet is desired such that
   the home worker(s) can share things like printers, talk to home
   automation from their desk, and to avoid having large-bandwidth cross
   the corporate network unnecessarily.

   More about DNS expectations of enterprises.  ActiveDirectory is
   relevant here.

2.3.  Multi-homed to 3G/LTE

   [SERVER-SELECTION] Section 3.2 "Cellular Network Scenario" provides
   more details.

   There is a problem here: so far it sounds like it's just IP TV over

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3.  Walled Garden DNS

   [SERVER-SELECTION] proposes a solution where ISP/connectivity
   providers provide a suffix, such as "mytv.example." or even
   unregistered names like ".internal" (common with ActiveDirectory)
   into the homenet.

   Along with suffix are provided one or more DNS servers, accessible
   via the semi-private connection, which would resolve names in that

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4.  Using Secret-Gardens to accomplish goals

   As [SERVER-SELECTION] essentially mandates that DNSSEC be done, it
   has essentially mandated that a recursive cacheing validating name
   server be run on each host.  Many have suggested that, as the days of
   20Mhz, 8MB workstations are long gone, that having a caching,
   validating name server on every host is not a problem.  Once one
   assumes this, new solutions become possible.

   The fundamental problem that [SERVER-SELECTION] tries to solve is
   that of mapping DNS suffixes to name servers.  [RFC1034] provides a
   way to do this: the NS resource record.  [DNSSEC] provides a way to
   do this securely by adding the DS resource record.

   So what was stopping enterprises such as IP TV, or corporate VPNs
   from putting in-accessible IP addresses into a reachable DNS server?
   Usually two things: the perception that the security through
   obscurity benefit of split-horizon DNS provided was greater than the
   operational complexity and inconvenience of using a single namespace.
   The second thing was that putting RFC1918 addresses in a publically
   visible DNS would be confusing.

   IPv6 addresses removes both problems.  First, since almost every
   walled-garden situation insists that any machine talking to it use an
   address in the prefix that the walled-garden provides.  This means
   that if one puts the DNS servers for the walled garden names in the
   walled gareden then can be queried only from machines that are
   already in the garden.

   Second: since IPv6 addresses are all unique, there is no confusion
   when an IPv6 address is listed.  It is therefore possible to
   unambiguously indicate in an NS that that mytv.example.com is
   reachable via DOCPREFIX:1234:0001.  Just because the entire Internet
   can see the (possibly secure) delegation doesn't meant that they can
   query it.

4.1.  Example 1: Corporate VPN

   A company EXAMPLE has been given the assignment 2001:DB8:0F00:/48.
   It has the forward name example.com.  In addition, due to an
   acquisition, it also owns example.org and assignment 2001:DB8:
   0123:/48.  Further, assume the VPN concentrator for example.com gives
   /128 tunnel addresses to clients from the 2001:DB8:0F00:ff91::/64
   range.  In this example, the client has been assigned 2001:DB8:0F00:

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      Routes are established through the VPN tunnel for the above two

   % netstat -rn -f inet6
   Routing tables

   Destination           Gateway                    Flags     Interface
   2001:db8:0f00::/48    2001:db8:0f00:ff91::1      UGRS      ipsec0
   2001:db8:0123::/48    2001:db8:0f00:ff91::1      UGRS      ipsec0

                                 Figure 1

   Rather than create a split-horizon DNS server on the inside that
   answers (differently) for example.com, the enterprise instead creates
   a new zone internal.example.com:

   % dig internal.example.com. ns
   ;internal.example.com.             IN      NS

   internal.example.com.  7200    IN    NS     ns1.internal.example.com.
   internal.example.com.  7200    IN    NS     ns2.internal.example.com.

   ns1.internal.example.com.  7200 IN   AAAA   2001:db8:0f00:0001::8888
   ns2.internal.example.com.  7200 IN   AAAA   2001:db8:0f00:0002::8888

                                 Figure 2

   Note that these records are in the public example.com zone, and are
   visible to the Internet.

   The ns1 and ns2 servers SHOULD be configured such that they will not
   answer queries for internal.example.com, unless the query comes from

   What is the effect here?  A host with it's VPN active performs a
   query for thing.internal.example.com.  The local recursive DNS server
   chases the NS pointers from the root, and it gets the above NS
   records.  It then performs a query to ns1.internal.example.com for
   the name thing.internal.example.com.  Since the route for this IP
   address goes through the ipsec0 device, the source address for the
   packet will be 2001:DB8:0F00:ff91::1234.  That source address fits
   into the policy for the ns1 server, so it answers.

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   There are a number of other affects: 1) the result of this lookup is
   cacheable, and does not need to be flushed if the node moves. 2) if
   the VPN is not active, then the result of performing the lookup for
   thing.internal.example.com causes a packet to be sent to the 2001:
   db8:0f00::/48 network.  If policies are setup right, then this packet
   may well cause the VPN to be started (or even restarted, if it

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5.  How does this differ from SERVER-SELECTION?

   run through use cases, show how this is equivalent or better.

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6.  Security Considerations

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7.  Other Related Protocols

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8.  IANA Considerations

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9.  Acknowledgements

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10.  References

10.1.  Informative References

10.2.  Normative References

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11.  Normative references

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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Author's Address

   Michael C. Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z 5V7

   Email: mcr+ietf@sandelman.ca
   URI:   http://www.sandelman.ca/

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