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Network Working Group                                         F. Templin
Internet-Draft                              Boeing Research & Technology
Intended status: Experimental                               May 09, 2012
Expires: November 10, 2012


                             ISATAP Updates
                     draft-templin-isupdate-04.txt

Abstract

   Many end user sites in the Internet today still have predominantly
   IPv4 internal infrastructures.  These sites range in size from small
   home/office networks to large corporate enterprise networks, but
   share the commonality that IPv4 continues to provide operational
   internal routing and addressing services for most applications.  As
   more and more IPv6-only services are deployed, however, end user
   devices within such sites will increasingly require at least basic
   IPv6 functionality.  This document therefore discusses updates to the
   Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) to better
   accommodate these needs.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 10, 2012.

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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  ISATAP Updates . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Advanced IPv6 Services Enabled by Updates  . . . . . . . . . .  5
     4.1.  Advertising ISATAP Router Behavior . . . . . . . . . . . .  6
     4.2.  ISATAP Host Behavior . . . . . . . . . . . . . . . . . . .  6
     4.3.  Non-Advertising ISATAP Router Behavior . . . . . . . . . .  6
     4.4.  Reference Operational Scenario . . . . . . . . . . . . . .  7
     4.5.  Site Administration Guidance . . . . . . . . . . . . . . . 10
     4.6.  On-Demand Dynamic Routing  . . . . . . . . . . . . . . . . 11
     4.7.  Loop Avoidance . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Manual Configuration . . . . . . . . . . . . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14























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1.  Introduction

   End user sites in the Internet today currently use IPv4 routing and
   addressing internally for core operating functions such as web
   browsing, filesharing, network printing, e-mail, teleconferencing and
   numerous other site-internal networking services.  Such sites
   typically have an abundance of public or private IPv4 addresses for
   internal networking, and are separated from the public Internet by
   firewalls, packet filtering gateways, proxies, address translators
   and other site border demarcation devices.  To date, such sites have
   had little incentive to enable IPv6 services internally [RFC1687].

   End-user sites that currently use IPv4 services internally come in
   endless sizes and varieties.  For example, a home network behind a
   Network Address Translator (NAT) may consist of a single link
   supporting a few laptops, printers etc.  As a larger example, a small
   business may consist of one or a few offices with several networks
   connecting considerably larger numbers of computers, routers,
   handheld devices, printers, faxes, etc.  Moving further up the scale,
   large banks, restaurants, major retailers, large corporations, etc.
   may consist of hundreds or thousands of branches worldwide that are
   tied together in a complex global enterprise network.  Additional
   examples include personal-area networks, mobile vehicular networks,
   disaster relief networks, tactical military networks, and various
   forms of Mobile Ad-hoc Networks (MANETs), etc.

   With the proliferation of IPv6 devices in the public Internet,
   however, existing IPv4 sites will increasingly require a means for
   enabling IPv6 services so that hosts within the site can communicate
   with IPv6-only correspondents.  Such services must be deployable with
   minimal configuration, and in a fashion that will not cause
   disruptions to existing IPv4 services.  The Intra-Site Automatic
   Tunnel Addressing Protocol (ISATAP) [RFC5214] provides a simple-to-
   use service that sites can deploy in the near term to meet these
   requirements, as discussed in [I-D.templin-v6ops-isops].  However,
   the ISATAP base specification has several fundamental limitations
   that make for a "spartan" IPv6 service.  This document discusses the
   motivations for new functionality followed by the updates and
   operational practices necessary to provide a more fully-functioned
   service.


2.  Motivation

   The base ISATAP specification does not support stateful address
   configuration nor prefix delegation (e.g., via DHCPv6
   [RFC3315][RFC3633]) on ISATAP interfaces.  Instead, the base
   specification requires a special IPv6 address format in which a



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   node's site-internal IPv4 address is embedded literally within the
   interface identifier of its public IPv6 address.  This exposes the
   site-internal IPv4 address structure to IPv6 networks and
   correspondents outside of the site.  Furthermore, static linkage of
   the node's site-internal IPv4 address to its public IPv6 address
   limits the node's ability to renumber its IPv4 address without also
   deprecating the IPv6 address.  These limitations may be more of a
   concern in some ISATAP deployments than others, but can be obviated
   by address configuration methods that support non-ISATAP interface
   identifiers.

   The ISATAP base specification further does not support router-to-
   router tunneling, i.e., it permits only router-to-host and host-to-
   host tunneling.  In practical terms, the ISATAP base specification
   therefore does not allow for deployment of "stub" IPv6-only networks
   inside of a parent site.  Examples include an IPv6-only bluetooth
   network of embedded devices, a laptop user's personal-area network,
   an IPv6-only fileshare workgroup, etc.  Without updates to the ISATAP
   base specification, these limitations could only be addressed by a
   site-wide native IPv6 deployment, which the site may not be prepared
   to finance or support in the near term.

   Finally, the base specification provides no means for address
   selection preference of IPv4 over ISATAP for communications within
   the same site.  Although this need could be addressed in the future
   by a DHCP option [I-D.ietf-6man-addr-select-opt], it may be necessary
   or preferable in some environments for ISATAP clients to discover
   address selection preferences only from the information advertised by
   ISATAP routers.  This document therefore specifies updates to the
   base specification to address these needs.


3.  ISATAP Updates

   The basic ISATAP model supports two basic node types - namely,
   advertising ISATAP routers and ISATAP hosts.  Advertising ISATAP
   routers configure their site-facing ISATAP interfaces as advertising
   router interfaces (see: [RFC4861], Section 6.2.2).  ISATAP hosts
   configure their site-facing ISATAP interfaces as simple host
   interfaces and also coordinate their autoconfiguration operations
   with advertising ISATAP routers.

   This document introduces a third node type known as "non-advertising
   ISATAP routers".  Non-advertising ISATAP routers configure their
   site-facing ISATAP interfaces as non-advertising router interfaces
   and obtain IPv6 addresses/prefixes via manual or automatic
   configuration arrangements with advertising ISATAP routers.  Non-
   advertising ISATAP routers connect IPv6 networks to the ISATAP link,



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   and can therefore support a router-to-router tunneling mode not
   supported under the base specification.

   To support this router-to-router tunneling (and also to support the
   assignment of native IPv6 addresses on ISATAP interfaces) ISATAP
   nodes add an update to the existing source address verification
   checks specified in Section 7.3 of [RFC5214].  Namely, the node also
   considers the outer IPv4 source address correct for the inner IPv6
   source address if:

   o  a stateful address mapping exists that lists the packet's IPv4
      source address as the link-layer address corresponding to the
      inner IPv6 source address via the ISATAP interface.

   The basic ISATAP model further does not specify any IPv6 multicast
   mappings.  This precludes the use of services such as DHCPv6 which
   require a link-scoped IPv6 multicasting service.  To support DHCPv6
   services, ISATAP hosts and non-advertising ISATAP routers that
   observe this specification map the IPv6
   "All_DHCP_Relay_Agents_and_Servers" link-scoped multicast address to
   the IPv4 address of an advertising ISATAP router that advertises
   availability of the DHCPv6 service.  The advertising ISATAP router in
   turn configures a DHCPv6 server or relay function, and accepts DHCPv6
   messages sent by clients using this mapping.  The advertising router
   also maintains a stateful address mapping that lists the IPv4 address
   of the client as the link-layer address of any delegated IPv6
   addresses or prefixes.

   Finally, this document updates the address selection policies of the
   base specification as follows.  For communications between two nodes
   whose IPv6 addresses are covered by the same IPv6 prefix advertised
   in Router Advertisements (RAs) on an ISATAP interface, prefer IPv4
   over IPv6 if the L bit in the Prefix Information Option (PIO) is set
   to 0.

   Using these updates, a much richer ISATAP service model is made
   possible.  The following sections describe the new modes of operation
   that are enabled by the updates.


4.  Advanced IPv6 Services Enabled by Updates

   Whether or not advertising ISATAP routers make stateless IPv6
   services available using StateLess Address AutoConfiguration (SLAAC),
   they can also provide advanced IPv6 services to ISATAP clients (i.e.,
   both hosts and non-advertising ISATAP routers) using the updates
   specified in this document.  Any addresses/prefixes obtained via the
   advanced (stateful) services are distinct from any IPv6 prefixes



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   advertised on the ISATAP interface for SLAAC purposes, however.

   The following sections discuss operational considerations for
   enabling ISATAP DHCPv6 services within predominantly IPv4 sites.

4.1.  Advertising ISATAP Router Behavior

   Advertising ISATAP routers that support DHCPv6 services send IPv6-in-
   IPv4 encapsulated RA messages that advertise availability of the
   service in response to IPv6-in-IPv4 encapsulated Router Solicitation
   (RS) messages received on an advertising ISATAP interface.  They also
   configure either a DHCPv6 relay or server function to service DHCPv6
   requests received from ISATAP clients.

4.2.  ISATAP Host Behavior

   ISATAP hosts send RS messages to obtain RA messages from an
   advertising ISATAP router.  When the DHCPv6 service is available, the
   host can acquire IPv6 addresses through the use of DHCPv6 stateful
   address autoconfiguration [RFC3315] whether or not IPv6 prefixes for
   SLAAC are advertised.  To acquire addresses, the host performs
   standard DHCPv6 exchanges while mapping the IPv6
   "All_DHCP_Relay_Agents_and_Servers" link-scoped multicast address to
   the IPv4 address of an advertising ISATAP router that supports the
   DHCPv6 service.

   After the host receives IPv6 addresses, it assigns them to its ISATAP
   interface and forwards any of its outbound IPv6 packets via the
   advertising router as a default router.  The advertising router in
   turn maintains stateful address mappings that list the IPv4 address
   of the host as the link-layer address of the delegated IPv6
   addresses.  Note that IPv6 addresses acquired from DHCPv6 therefore
   need not be ISATAP addresses, i.e., even though the addresses are
   assigned to the ISATAP interface.

4.3.  Non-Advertising ISATAP Router Behavior

   Non-advertising ISATAP routers send RS messages to obtain RA messages
   from an advertising ISATAP router, i.e., they act as "hosts" on their
   non-advertising ISATAP interfaces.  Non-advertising ISATAP routers
   can acquire IPv6 prefixes through the use of DHCPv6 Prefix Delegation
   [RFC3633] via an advertising router that supports DHCPv6 services in
   the same fashion as described above for host-based address
   autoconfiguration.  The advertising router in turn maintains stateful
   address mappings that list the IPv4 address of the non-advertising
   router as the link-layer address of the next hop toward the delegated
   IPv6 prefixes.




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   In many use case scenarios (e.g., small enterprise networks, small
   and stable MANETs, etc.), advertising and non-advertising ISATAP
   routers can engage in a proactive dynamic IPv6 routing protocol
   (e.g., OSPFv3, RIPng, etc.) over their ISATAP interfaces so that IPv6
   routing/forwarding tables can be populated and standard IPv6
   forwarding between ISATAP routers can be used.  In other scenarios
   (e.g., large enterprise networks, large and dynamic MANETs, etc.),
   this might be impractical due to scaling issues.

   After the non-advertising ISATAP router acquires IPv6 prefixes, it
   can sub-delegate them to routers and links within its attached IPv6
   edge networks, then can forward any outbound IPv6 packets coming from
   its edge networks via other nodes on the ISATAP link.

4.4.  Reference Operational Scenario

   Figure 1 depicts a reference ISATAP network topology enabled by the
   updated ISATAP services specified in this document.  The scenario
   shows two advertising ISATAP routers ('A', 'B'), two non-advertising
   ISATAP routers ('C', 'E'), an ISATAP host ('G'), and three ordinary
   IPv6 hosts ('D', 'F', 'H') in a typical deployment configuration:






























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                    .-(::::::::)      2001:db8:3::1
                 .-(::: IPv6 :::)-.  +-------------+
                (:::: Internet ::::) | IPv6 Host H |
                 `-(::::::::::::)-'  +-------------+
                    `-(::::::)-'
                ,~~~~~~~~~~~~~~~~~,
           ,----|companion gateway|--.
          /     '~~~~~~~~~~~~~~~~~'  :
         /                           |.
      ,-'                              `.
     ;  +------------+   +------------+  )
     :  |  Router A  |   |  Router B  |  /
      : |  (isatap)  |   |  (isatap)  |  :    fe80::*192.0.2.4
      : | 192.0.2.1  |   | 192.0.2.1  | ;       2001:db8:2::1
      + +------------+   +------------+  \    +--------------+
     fe80::*:192.0.2.1   fe80::*:192.0.2.1    |   (isatap)   |
     |                                   ;    |    Host G    |
     :              IPv4 Site         -+-'    +--------------+
      `-.       (PRL: 192.0.2.1)       .)
         \                           _)
          `-----+--------)----+'----'
     fe80::*:192.0.2.2        fe80::*:192.0.2.3         .-.
     +--------------+         +--------------+       ,-(  _)-.
     |   (isatap)   |         |   (isatap)   |    .-(_ IPv6  )-.
     |   Router C   |         |   Router E   |--(__Edge Network )
     +--------------+         +--------------+     `-(______)-'
      2001:db8:0::/48          2001:db8:1::/48           |
             |                                     2001:db8:1::1
            .-.                                   +-------------+
         ,-(  _)-.      2001:db8:0::1             | IPv6 Host F |
      .-(_ IPv6  )-.   +-------------+            +-------------+
    (__Edge Network )--| IPv6 Host D |
       `-(______)-'    +-------------+

   (* == "5efe")

                Figure 1: Reference ISATAP Network Topology

   In Figure 1, advertising ISATAP routers 'A' and 'B' within the IPv4
   site provide DHCPv6 services and connect to the IPv6 Internet either
   directly or via a companion gateway.  The advertising routers both
   configure the IPv4 anycast address 192.0.2.1 on a site-interior IPv4
   interface, and configure an advertising ISATAP interface with link-
   local ISATAP address fe80::5efe:192.0.2.1.  The site administrator
   then places the single IPv4 address 192.0.2.1 in the Potential Router
   List (PRL) for the site.  'A' and 'B' then both advertise the anycast
   address/prefix into the site's IPv4 routing system so that ISATAP
   clients can locate the router that is topologically closest.  (Note:



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   advertising ISATAP routers can instead use individual IPv4 unicast
   addresses instead of a shared IPv4 anycast address.  In that case,
   the PRL may contain multiple IPv4 addresses of advertising routers.)

   Non-advertising ISATAP router 'C' connects to one or more IPv6 edge
   networks and also connects to the site via an IPv4 interface with
   address 192.0.2.2.  'C' next configures a non-advertising ISATAP
   router interface with link-local ISATAP address fe80::5efe:192.0.2.2,
   then discovers router 'A' via an RS/RA exchange.  'C' next receives
   the IPv6 prefix 2001:db8:0::/48 through a DHCPv6 prefix delegation
   exchange via 'A', then engages in an IPv6 routing protocol over its
   ISATAP interface and announces the delegated IPv6 prefix.  'C'
   finally sub-delegates the prefix to its attached edge networks, where
   IPv6 host 'D' autoconfigures the address 2001:db8:0::1.

   Non-advertising ISATAP router 'E' connects to the site, configures
   its ISATAP interface, performs an RS/RA exchange, receives a DHCPv6
   prefix delegation, and engages in the IPv6 routing protocol the same
   as for 'C'.  In particular, 'E' configures the IPv4 address 192.0.2.3
   and the link-local ISATAP address fe80::5efe:192.0.2.3.  'E' then
   receives the delegated IPv6 prefix 2001:db8:1::/48 and sub-delegates
   the prefix to its attached edge networks, where IPv6 host 'F'
   autoconfigures IPv6 address 2001:db8:1::1.

   ISATAP host 'G' connects to the site via an IPv4 interface with
   address 192.0.2.4, and also configures an ISATAP host interface with
   link-local ISATAP address fe80::5efe:192.0.2.4 over the IPv4
   interface.  'G' next performs an RS/RA exchange to discover 'B" and
   configures a default IPv6 route with next-hop address fe80::5efe:
   192.0.2.1.  'G' then receives the IPv6 address 2001:db8:2::1 via a
   DHCPv6 address configuration exchange via 'B'; it then assigns the
   address to the ISATAP interface but does not assign a non-link-local
   IPv6 prefix to the interface.

   Finally, IPv6 host 'H' connects to an IPv6 network outside of the
   ISATAP domain.  'H' configures its IPv6 interface in a manner
   specific to its attached IPv6 link, and autoconfigures the IPv6
   address 2001:db8:3::1.

   Following this autoconfiguration, when host 'D' has an IPv6 packet to
   send to host 'F', it prepares the packet with source address 2001:
   db8:0::1 and destination address 2001:db8:1::1, then sends the packet
   into the edge network where IPv6 forwarding will eventually convey it
   to router 'C'.  'C' then uses IPv6-in-IPv4 encapsulation to forward
   the packet to router 'E', since it has discovered a route to 2001:
   db8:1::/48 with next hop 'E' via dynamic routing over the ISATAP
   interface.  Router 'E' finally sends the packet into the edge network
   where IPv6 forwarding will eventually convey it to host 'F'.



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   In a second scenario, when 'D' has a packet to send to ISATAP host
   'G', it prepares the packet with source address 2001:db8:0::1 and
   destination address 2001:db8:2::1, then sends the packet into the
   edge network where it will eventually be forwarded to router 'C' the
   same as above.  'C' then uses IPv6-in-IPv4 encapsulation to forward
   the packet to router 'A' (i.e., 'C's default router), which in turn
   forwards the packet to 'G'.  Note that this operation entails two
   hops across the ISATAP link (i.e., one from 'C' to 'A', and a second
   from 'A' to 'G').  If 'G' also participates in the dynamic IPv6
   routing protocol, however, 'C' could instead forward the packet
   directly to 'G' without involving 'A'.

   In a third scenario, when 'D' has a packet to send to host 'H' in the
   IPv6 Internet, the packet is forwarded to 'C' the same as above.  'C'
   then forwards the packet to 'A', which forwards the packet into the
   IPv6 Internet.

   In a final scenario, when 'G' has a packet to send to host 'H' in the
   IPv6 Internet, the packet is forwarded directly to 'B', which
   forwards the packet into the IPv6 Internet.

4.5.  Site Administration Guidance

   Site administrators configure advertising ISATAP routers that also
   support the DHCPv6 relay/server function to send RA messages with the
   M flag set to 1 as an indication to clients that the stateful DHCPv6
   address autoconfiguration services are available.  If stateless
   DHCPv6 services are also available, the RA messages also set the O
   flag to 1.

   Gateways and packet filtering devices of various forms are often
   deployed in order to divide the site into separate partitions.
   Although the purely stateful model does not involve the advertisement
   of non-link-local IPv6 prefixes on ISATAP interfaces, alignment of
   IPv6 prefixes used for stateful address assignment with IPv4 site
   partitions is still recommended so that ISATAP clients can prefer
   native IPv4 communications over ISATAP IPv6 services for
   correspondents within their contiguous IPv4 partition.

   For example, if the site is assigned the aggregate prefix 2001:db8:
   0::/48, then the site administrators can assign the more-specific
   prefixes 2001:db8:0:0::/64, 2001:db8:0:1::/64, 2001:db8:0:2::/64,
   etc. to the different IPv4 partitions within the site.  The
   administrators can then institute a policy that prefers native IPv4
   addresses for communications between clients covered by the same /64
   prefix.

   Site administrators can implement this policy implicitly by



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   configuring advertising ISATAP routers to advertise each /64 prefix
   with both the A and L flags set to 0 as an indication that IPv4
   should be preferred over IPv6 destinations that configure addresses
   from the same prefix.  Site administrators can instead (or in
   addition) implement address selection policy rules [RFC3484] through
   explicit configurations in each ISATAP client.

   For example, each ISATAP client associated with the prefix 2001:db8:
   0:0::/64 can add the prefix to its address selection policy table
   with a lower precedence than the prefix ::ffff:0:0/96.  In this way,
   IPv4 addresses are preferred over IPv6 addresses from within the same
   /64 prefix.  The prefix could be added to each ISATAP client either
   manually, or through an automated service such as a DHCP option
   [I-D.ietf-6man-addr-select-opt].  In this way, clients will use IPv4
   communications to reach correspondents within the same IPv4 site
   partition, and will use IPv6 communications to reach correspondents
   in other partitions and/or outside of the site.

   When the PRL includes an anycast address, the client may be directed
   to a first DHCPv6 relay/server in initial message exchanges and to a
   different relay/server in subsequent exchanges.  In order to address
   this uncertainty, site administrators should configure DHCPv6 servers
   to include a Server Unicast option so that clients can remain
   associated with the same server that was reached during the initial
   exchange.  (Alternatively, the administrator could arrange for the
   site's DHCPv6 servers to maintain a distributed database of client
   bindings.)

   Finally, site administrators should configure ISATAP routers to not
   send ICMPv6 Redirect messages to inform a source client of a better
   next hop toward the destination unless there is strong assurance that
   the client and the next hop are within the same IPv4 site partition.

4.6.  On-Demand Dynamic Routing

   With respect to the reference operational scenarios depicted in
   Figure 1, there may be use cases in which a proactive dynamic IPv6
   routing protocol cannot be used.  For example, in large enterprise
   network deployments it would be impractical for all ISATAP routers to
   engage in a common routing protocol instance due to scaling
   considerations.

   In those cases, an on-demand routing capability can be enabled in
   which ISATAP nodes send initial packets via an advertising ISATAP
   router and receive redirection messages back.  For example, when a
   non-advertising ISATAP router 'C' has a packet to send to a host
   located behind non-advertising ISATAP router 'E', it can send the
   initial packets via advertising router 'A' which will return



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   redirection messages to inform 'C' that 'E' is a better first hop.
   Protocol details for this redirection procedure (including a means
   for detecting whether the direct path is usable) are specified in
   [I-D.templin-aero].

4.7.  Loop Avoidance

   When no advertising ISATAP routers advertise IPv6 prefixes for SLAAC
   purposes, no non-link-local IPv6 prefixes are assigned to ISATAP
   router interfaces.  In that case, an ISATAP router cannot mistake
   another router for an ISATAP host due to an address that matches an
   on-link prefix.  This corresponds to the mitigation documented in
   Section 3.2.4 of [RFC6324].

   Any routing loops introduced in the stateful scenario would therefore
   be due to a misconfiguration in IPv6 routing the same as for any IPv6
   router, and hence are out of scope for this document.


5.  Manual Configuration

   In addition to any SLAAC and/or DHCPv6 services, when the updates in
   this document are employed site administrators can use manual
   configuration to assign non-ISATAP IPv6 addresses to the ISATAP
   interfaces of client end systems.  Site administrators can also use
   manual configuration to assign IPv6 prefixes to non-advertising
   ISATAP routers instead of (or in addition to) using DHCPv6 prefix
   delegation.

   The IPv6 prefixes used for manual configuration must be distinct from
   any prefixes used for SLAAC, however they may overlap with the
   prefixes used for DHCPv6 as long as there is administrative assurance
   that the same IPv6 addresses/prefixes will not be delegated by both
   DHCPv6 and manual configuration.  The manual configuration scenarios
   and routing considerations are otherwise the same as discussed in
   Section 4.

   When manually configured IPv6 addresses/prefixes are used, the
   prefixes must be covered by a shorter IPv6 prefix advertised into the
   IPv6 routing system by one or more advertising ISATAP routers.  The
   advertising routers must further maintain stateful address mappings
   that associate the addresses/prefixes with the ISATAP clients to
   which the addresses/prefixes are delegated, i.e., the same as for
   DHCPv6.







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6.  IANA Considerations

   This document has no IANA considerations.


7.  Security Considerations

   In addition to the security considerations documented in [RFC5214],
   sites that use ISATAP should take care to ensure that no routing
   loops are enabled [RFC6324].  Additional security concerns with IP
   tunneling are documented in [RFC6169].


8.  Acknowledgments

   The following are acknowledged for their insights that helped shape
   this work: Dmitry Anipko, Fred Baker, Ron Bonica, Brian Carpenter,
   Remi Despres, Thomas Henderson, Philip Homburg, Lee Howard, Ray
   Hunter, Joel Jaeggli, John Mann, Gabi Nakibly, Christoper Palmer,
   Hemant Singh, Mark Smith, Dave Thaler, Ole Troan, and Gunter Van de
   Velde.


9.  References

9.1.  Normative References

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.

9.2.  Informative References

   [I-D.ietf-6man-addr-select-opt]
              Matsumoto, A., Fujisaki, T., Kato, J., and T. Chown,
              "Distributing Address Selection Policy using DHCPv6",



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              draft-ietf-6man-addr-select-opt-03 (work in progress),
              February 2012.

   [I-D.templin-aero]
              Templin, F., "Asymmetric Extended Route Optimization
              (AERO)", draft-templin-aero-08 (work in progress),
              February 2012.

   [I-D.templin-v6ops-isops]
              Templin, F., "Operational Guidance for IPv6 Deployment in
              IPv4 Sites using ISATAP", draft-templin-v6ops-isops-16
              (work in progress), May 2012.

   [RFC1687]  Fleischman, E., "A Large Corporate User's View of IPng",
              RFC 1687, August 1994.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC5720]  Templin, F., "Routing and Addressing in Networks with
              Global Enterprise Recursion (RANGER)", RFC 5720,
              February 2010.

   [RFC6169]  Krishnan, S., Thaler, D., and J. Hoagland, "Security
              Concerns with IP Tunneling", RFC 6169, April 2011.

   [RFC6324]  Nakibly, G. and F. Templin, "Routing Loop Attack Using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", RFC 6324, August 2011.


Author's Address

   Fred L. Templin
   Boeing Research & Technology
   P.O. Box 3707 MC 7L-49
   Seattle, WA  98124
   USA

   Email: fltemplin@acm.org











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