[Search] [txt|pdf|bibtex] [Tracker] [Email] [Nits]

Versions: 00                                                            
Network Working Group                                        B. Sarikaya
Internet-Draft                                                Huawei USA
Intended status: Standards Track                           June 20, 2014
Expires: December 22, 2014


       DHCPv6 Route Options for Source Address Dependent Routing
              draft-sarikaya-dhc-dhcpv6-raoptions-sadr-00

Abstract

   This document describes DHCPv6 Route Options for provisioning IPv6
   routes on DHCPv6 client nodes for source address dependent routing.
   Using these options, an operator can configure multi-homed nodes
   where other means of route configuration may be impractical.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 December 22, 2014.

Copyright Notice

   Copyright (c) 2014 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



Sarikaya                Expires December 22, 2014               [Page 1]


Internet-Draft                                                 June 2014


   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  DHCPv6 Based Solution . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Default route configuration . . . . . . . . . . . . . . .   3
     2.2.  Configuring on-link routes  . . . . . . . . . . . . . . .   4
     2.3.  Deleting obsolete route . . . . . . . . . . . . . . . . .   4
     2.4.  Applicability to routers  . . . . . . . . . . . . . . . .   5
     2.5.  Updating Routing Information  . . . . . . . . . . . . . .   5
     2.6.  Limitations . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  DHCPv6 Route Options  . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Route Prefix Option Format  . . . . . . . . . . . . . . .   7
     3.2.  Next Hop Option Format  . . . . . . . . . . . . . . . . .   8
     3.3.  Source Address/Prefix Option Format . . . . . . . . . . .   9
   4.  DHCPv6 Server Behavior  . . . . . . . . . . . . . . . . . . .  10
   5.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . . . . . .  11
     5.1.  Conflict resolution . . . . . . . . . . . . . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   The Neighbor Discovery (ND) protocol [RFC4861] provides a mechanism
   for hosts to discover one or more default routers on a directly
   connected network segment.  Extensions to the Router Advertisement
   (RA) protocol defined in [RFC4191] allow hosts to discover the
   preferences for multiple default routers on a given link, as well as
   any specific routes advertised by these routers.  This provides
   network administrators with a new set of tools to handle multi-homed
   host topologies and influence the route selection by the host.  This
   ND based mechanism however is sub optimal or impractical in some
   multi-homing scenarios, e.g. source address dependent routing.  Both
   Router Advertisement options [I-D.sarikaya-6man-next-hop-ra] and
   DHCPv6 can be used.  In networks that deployed DHCPv6, the use of
   DHCPv6 [RFC3315] is seen to be more viable.





Sarikaya                Expires December 22, 2014               [Page 2]


Internet-Draft                                                 June 2014


   DHCPv6 Route Options defined in this document can be used to
   configure fixed and mobile nodes in multi-homed scenarios with route
   information and next hop address.  Different scenarios exist such as
   the node is simultaneously connected to multiple access network of
   e.g.  WiFi and 3G.  The node may also be connected to more than one
   gateway.  Such connectivity may be realized by means of dedicated
   physical or logical links that may also be shared with other users
   nodes such as in residential access networks.

   A document defining topologies and in general providing an overview
   of the issue of source address dependent routing is TBD.

   The solution presented in this document is part of the network
   configuration information.  A consistent set of network configuration
   is defined as Provisioning Domain (PvD) [I-D.ietf-mif-mpvd-arch].
   PvDs or so-called explicit PvDs may include information related to
   more than one interfaces as is the case in this document.  It is
   important to note that the node has a trust relationship with the
   PvD, in such a case, it is called trusted PvD.  The trust is
   established using authorization and authentication between the node
   that is using the PvD configuration and the source that provided that
   configuration.  In this document, we assume that DHCP server can
   provide trusted PvDs to the hosts.

2.  DHCPv6 Based Solution

   A DHCPv6 based solution allows an operator an on demand and node
   specific means of configuring static routing information.  Such a
   solution also fits into network environments where the operator
   prefers to manage Residential Gateway (RG) configuration information
   from a centralized DHCP server.  [RFC7157] provides additional
   background to the need for a DHCPv6 solution to the problem.

   In terms of the high level operation of the solution defined in this
   draft, a DHCPv6 client interested in obtaining routing information
   requests the route options using the DHCPv6 Option Request Option
   (ORO) sent to a server.  A Server, when configured to do so, provides
   the requested route information as part of a nested options structure
   covering; the next-hop address; the destination prefix; the route
   metric; any additional options applicable to the destination or next-
   hop.

2.1.  Default route configuration

   A non-trustworthy network may be available at the same time as a
   trustworthy network, with the risk of bad consequences if the host
   gets confused between the two.  These are basically the two models
   for hosts with multiple interfaces, both of which are valid, but



Sarikaya                Expires December 22, 2014               [Page 3]


Internet-Draft                                                 June 2014


   which are incompatible with each other.  In the first model, an
   interface is connected to something like a corporate network, over a
   Virtual Private Network (VPN).  This connection is trusted because it
   has been authenticated.  Routes obtained over such a connection can
   probably be trusted, and indeed it may be important to use those
   routes.  This is because in the VPN case, you may also be connected
   to a network that's offered you a default route, and you could be
   attacked over that connection if you attempt to connect to resources
   on the enterprise network over it.

   On the other, non-trustworthy network scenario, none of the networks
   to which the host is connected are meaningfully more or less
   trustworthy.  In this scenario, the untrustworthy network may hand
   out routes to other hosts, e.g. those in the VPN going through some
   malicious nodes.  This will have bad consequences because the host's
   traffic intended for the corporate VPN may be hijacked by the
   intermediate nodes.

   DHCPv6 options described in this document can be used to install the
   routes.  However, the use of such a technique makes sense only in the
   former case above, i.e. trusted network.  So the host MUST have an
   authenticated connection to the network it connects so that DHCPv6
   route options can be trusted before establishing routes.

   Server MUST NOT define more than one default route.

2.2.  Configuring on-link routes

   Server may also configure on-link routes, i.e. routes that are
   available directly over the link, not via routers.  To specify on-
   link routes, server MAY include RTPREFIX option directly in Advertise
   and Reply messages.

2.3.  Deleting obsolete route

   There are two mechanisms that allow removing a route.  Each defined
   route has a route lifetime.  If specific route is not refreshed and
   its timer reaches 0, client MUST remove corresponding entry from
   routing table.

   In cases, where faster route removal is needed, server SHOULD return
   RT_PREFIX option with route lifetime set to 0.  Client that receives
   RT_PREFIX with route lifetime set to 0 MUST remove specified route
   immediately, even if its previous lifetime did not expire yet.







Sarikaya                Expires December 22, 2014               [Page 4]


Internet-Draft                                                 June 2014


2.4.  Applicability to routers

   Contrary to Router Adverisement mechanism, defined in [RFC4861] that
   explicitly limits configuration to hosts, routing configuration over
   DHCPv6 defined in this document may be used by both hosts and
   routers.  (This limitation of RA mechanism was partially lifted by
   W-1 requirement formulated in [RFC6204].)

   One of the envisaged usages for this solution are residential
   gateways (RG) or Customer Premises Equipment (CPE).  Those devices
   very often perform routing.  It may be useful to configure routing on
   such devices over DHCPv6.  One example of such use may be a class of
   premium users that are allowed to use dedicated router that is not
   available to regular users.

2.5.  Updating Routing Information

   Network configuration occassionally changes, due to failure of
   existing hardware, migration to newer equipment or many other
   reasons.  Therefore there a way to inform clients that routing
   information have changed is required.

   There are several ways to inform clients about new routing
   information.  Every client SHOULD periodically refresh its
   configuration, according to Information Refresh Time Option, so
   server may send updated information the next time client refreshes
   its information.  New routes may be configured at that time.  As
   every route has associated lifetime, client is required to remove its
   routes when this timer expires.  This method is particularly useful,
   when migrating to new router is undergoing, but old router is still
   available.

   Server MAY also announce routes via soon to be removed router with
   lifetimes set to 0.  This will cause the client to remove its routes,
   despite the fact that previously received lifetime may not yet
   expire.

   Aforementioned methods are useful, when there is no urgent need to
   update routing information.  Bound by timer set by value of
   Information Refresh Time Option, clients may use outdated routing
   information until next scheduled renewal.  Depending on configured
   value this delay may be not acceptable in some cases.  In such
   scenarios, administrators are advised to use RECONFIGURE mechanism,
   defined in [RFC3315].  Server transmits RECONFIRGURE message to each
   client, thus forcing it to immediately start renewal process.

   See also Section 2.6 about limitations regarding dynamic routing.




Sarikaya                Expires December 22, 2014               [Page 5]


Internet-Draft                                                 June 2014


2.6.  Limitations

   Defined mechanism is not intended to be used as a dynamic routing
   protocol.  It should be noted that proposed mechanism cannot
   automatically detect routing changes.  In networks that use dynamic
   routing and also employ this mechanism, clients may attempt using
   routes configured over DHCPv6 even though routers or specific routes
   ceased to be available.  This may cause black hole routing problem.
   Therefore it is not recommended to use this mechanism in networks
   that use dynamic routing protocols.  This mechanism SHOULD NOT be
   used in such networks, unless network operator can provide a way to
   update DHCP server information in case of router availability
   changes.

   Discussion: It should be noted that DHCPv6 server is not able to
   monitor health of existing routers.  As there are currently more than
   60 options defined for DHCPv6, it is infeasible to implement
   mechanism that would monitor huge set of services and stop announcing
   its availability in case of service outage.  Therefore in case of
   prolonged unavailability human interverntion is required to change
   DHCPv6 server configuration.  If that is considered a problem,
   network administrators should consider using other alternatives, like
   RA and ND mechanisms (see [RFC4861]).

3.  DHCPv6 Route Options

   A DHCPv6 client interested in obtaining routing information includes
   the NEXT_HOP and RT_PREFIX options as part of its Option Request
   Option (ORO) in messages directed to a server (as allowed by
   [RFC3315], i.e.  Solicit, Request, Renew, Rebind or Information-
   request messages).  A Server, when configured to do so, provides the
   requested route information using zero, one or more NEXT_HOP options
   in messages sent in response (Advertise, and Reply).  So as to allow
   the route options to be both extensible, as well as conveying
   detailed info for routes, use is made of a nested options structure.
   Server sends one or more NEXT_HOP options that specify the IPv6 next
   hop addresses.  Each NEXT_HOP option conveys in turn zero, one or
   more RT_PREFIX options that represents the IPv6 destination prefixes
   reachable via the given next hop.  Server includes RT_PREFIX directly
   in message to indicate that given prefix is available directly on-
   link.  Server MAY send a single NEXT_HOP without any RT_PREFIX
   suboptions or with RT_PREFIX that contains ::/0 to indicate available
   default route.  The Formats of the NEXT_HOP and RT_PREFIX options are
   defined in the following sub-sections.

   The DHCPv6 Route Options format borrows from the principles of the
   Route Information Option defined in [RFC4191].




Sarikaya                Expires December 22, 2014               [Page 6]


Internet-Draft                                                 June 2014


3.1.  Route Prefix Option Format

   The Route Prefix Option is used to convey information about a single
   prefix that represents the destination network.  The Route Prefix
   Option is used as a sub-option in the previously defined Next Hop
   Option.  It may also be sent directly in message to indicate that
   route is available directly on-link.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       OPTION_RT_PREFIX        |          option-len           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Route lifetime                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Prefix-Length |    Metric     |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                            Prefix                             |
   |                          (up to 16 octets)                    |
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: Route Prefix Option Format

   option-code:  OPTION_RT_PREFIX (TBD2).

   option-len:  Length of the Route Prefix option including all its sub-
             options.

   Route lifetime  32-bit unsigned integer.  Specifies lifetime of the
             route information, expressed in seconds (relative to the
             time the packet is sent).  There are 2 special values
             defined. 0 means that route is no longer valid and must be
             removed by clients.  A value of all one bits (0xffffffff)
             represents infinity.  means infinity.

   Prefix Length:  8-bit unsigned integer.  The length in bits of the IP
             Prefix.  The value ranges from 0 to 128.  This field
             represents the number of valid leading bits in the prefix.

   Resvd:    Reserved field.  Server MUST set this value to zero and
             client MUST ignore its content.

   Metric:   Route Metric. 8-bit signed integer.  The Route Metric
             indicates whether to prefer the next hop associated with




Sarikaya                Expires December 22, 2014               [Page 7]


Internet-Draft                                                 June 2014


             this prefix over others, when multiple identical prefixes
             (for different next hops) have been received.

   Prefix:   a variable size field that specifies Rule IPv6 prefix.
             Length of the field is defined by prefix6-len field and is
             rounded up to the nearest octet boundary (if case when
             Prefix Length is not divisible by 8).  In such case
             additional padding bits must be zeroed.

   Values for metric field have meaning based on the value, i.e. higher
   value indicates higher preference.

3.2.  Next Hop Option Format

   Each IPv6 route consists of an IPv6 next hop address, an IPv6
   destination prefix (a.k.a. the destination subnet), and a host
   preference value for the route.  Elements of such route (e.g.  Next
   hops and prefixes associated with them) are conveyed in NEXT_HOP
   option that contains RT_PREFIX suboptions.

   The Next Hop Option defines the IPv6 address of the next hop, usually
   corresponding to a specific next-hop router.  For each next hop
   address there can be zero, one or more prefixes reachable via that
   next hop.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        OPTION_NEXT_HOP        |          option-len           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                    IPv6 Next Hop Address                      |
   |                       (16 octets)                             |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                        NEXT_HOP sub-options                   |
   .                                                               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: IPv6 Next Hop Option Format

   option-code:  OPTION_NEXT_HOP (TBD1).

   option-len:  16 + Length of NEXT_HOP options field.





Sarikaya                Expires December 22, 2014               [Page 8]


Internet-Draft                                                 June 2014


   IPv6 Next Hop Address:  16 octet long field that specified IPv6
             address of the next hop.

   NEXT_HOP options:  Options associated with this Next Hop. This
             includes, but is not limited to, zero, one or more
             RT_PREFIX options that specify prefixes reachable through
             the given next hop.

   NEXT_HOP options:  Options associated with this Next Hop. This
             includes, but is not limited to, zero, one or more
             SOURCE_AP and RT_PREFIX options that specify prefixes
             reachable through the given next hop.

3.3.  Source Address/Prefix Option Format

   Each IPv6 route consists of an IPv6 next hop address, an IPv6
   destination prefix (a.k.a. the destination subnet), and a host
   preference value for the route.  Elements of such route (e.g.  Next
   hops and prefixes associated with them) are conveyed in NEXT_HOP
   option that contains RT_PREFIX suboptions.

   The Source Address/Prefix Option defines the source IPv6 prefix/
   address that are assigned from the prefixes that belong to this next
   hop.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        OPTION_SOURCE_AP        |          option-len           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Prefix-Length |  Reserved     |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |              IPv6 Source Address/Prefix                       |
   |                          (up to 16 octets)                    |
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 3: IPv6 Source Address/Prefix Option Format

   option-code:  OPTION_SOURCE_AP (TBD1).

   option-len:  16 + Length of SOURCE_AP options field.

   Prefix Length:  8-bit unsigned integer.  The length in bits of the IP
             Prefix.  The value ranges from 0 to 128.  This field




Sarikaya                Expires December 22, 2014               [Page 9]


Internet-Draft                                                 June 2014


             represents the number of valid leading bits in the prefix.
             In case of source address this field is set to 132.

   Resvd:    Reserved field.  Server MUST set this value to zero and
             client MUST ignore its content.

   IPv6 Source Address/Prefix:  16 octet long field that specified IPv6
             source address or source prefix.

4.  DHCPv6 Server Behavior

   When configured to do so, a DHCPv6 server shall provide the NEXT_HOP
   and RT_PREFIX Options in ADVERTISE and REPLY messages sent to a
   client that requested the route option.  Each Next Hop Option sent by
   the server must convey at least one Route Prefix Option.

   Server includes NEXT_HOP option with possible RT_PREFIX suboptions to
   designate that specific routes are available via routers.  Server
   includes RT_PREFIX options in Next Hop sub-options directly in
   Advertise and Reply messages to inform that specific routes are
   available directly on-link.

   If there is more than one route available via specific next hop,
   server MUST send only one NEXT_HOP for that next hop, which contains
   multiple RT_PREFIX options.  Server MUST NOT send more than one
   identical (i.e. with equal next hop address field) NEXT_HOP option.

   When configured to do so, a DHCPv6 server shall send one or more
   NEXT_HOP options that contain one or more source addresses Figure 3
   included in the Next Hop sub-options field.  Each Next Hop Address
   may be associated with zero, one or more Source Prefix that represent
   the source addresses that are assigned from the prefixes that belong
   to this next hop.  The Next Hop sub-options field MAY contain Route
   Prefix options that represent the IPv6 destination prefixes reachable
   via the given next hop as defined in Figure 2.  When configured to do
   so, a DHCPv6 server shall send NEXT_HOP option with Route Prefix
   option and Source Prefix in the message in the Next Hop sub-options
   field to indicate that given prefix is available directly on-link and
   that any source addresses derived from the source prefix will not be
   subject to ingress filtering on these routes supported by these next
   hops.

   When configured to do so, a DHCPv6 server shall send one or more
   NEXT_HOP option that specify the IPv6 next hop addresses and source
   address.  Each Next Hop Address option may be associated with zero,
   one or more Source Address that represent the source addresses that
   are assigned from the prefixes that belong to this next hop.  The
   Next Hop sub-options field shall contain Source Address Figure 3 and



Sarikaya                Expires December 22, 2014              [Page 10]


Internet-Draft                                                 June 2014


   Route Prefix options Figure 1 that represent the IPv6 destination
   prefixes reachable via the given next hop.  DHCPv6 server shall
   include Next Hop Address with Source Address and Route Prefix option
   in Next Hop sub-options field in the message to indicate that given
   prefix is available directly on-link and that the source address will
   not be subject to ingress filtering.  For the Source Address, Source
   Address/Prefix option Figure 3 is used with prefix length set to 128.

   Each Next Hop Address may be associated with zero, one or more Source
   Prefix that represent the source addresses that are assigned from the
   prefixes that belong to this next hop.  The option MAY contain Route
   Prefix options that represent the IPv6 destination prefixes reachable
   via the given next hop.  DHCP server shall include Next Hop Address
   with Route Prefix option in Next Hop sub-option field defined in
   Figure 2 in the message to indicate that given prefix is available
   directly on-link.  To indicate that any source addresses derived from
   the source prefix will not be subject to ingress filtering on these
   routes supported by these next hops DHCPv6 server shall send two
   options, Next Hop option with Route Prefix option in Next Hop options
   field and a Source Prefix option defined in Figure 3.

   Servers SHOULD NOT send NEXT_HOP or RT_PREFIX to clients that did not
   explicitly requested it, using the ORO.

   Servers MUST NOT send NEXT_HOP or RT_PREFIX in messages other than
   ADVERTISE or REPLY.

   Servers MAY also include Status Code Option, defined in Section 22.13
   of the [RFC3315] to indicate the status of the operation.

   Servers MUST include the Status Code Option, if the requested routing
   configuration was not successful and SHOULD use status codes as
   defined in [RFC3315] and [RFC3633].

   The maximum number of routing information in one DHCPv6 message
   depend on the maximum DHCPv6 message size defined in [RFC3315]

5.  DHCPv6 Client Behavior

   A DHCPv6 client compliant with this specification MUST request the
   NEXT_HOP and RT_PREFIX Options in an Option Request Option (ORO) in
   the following messages: Solicit, Request, Renew, Rebind, and
   Information-Request.  The messages are to be sent as and when
   specified by [RFC3315].

   When processing a received Route Options a client MUST substitute a
   received 0::0 value in the Next Hop Option with the source IPv6
   address of the received DHCPv6 message.  It MUST also associate a



Sarikaya                Expires December 22, 2014              [Page 11]


Internet-Draft                                                 June 2014


   received Link Local next hop addresses with the interface on which
   the client received the DHCPv6 message containing the route option.
   Such a substitution and/or association is useful in cases where the
   DHCPv6 server operator does not directly know the IPv6 next-hop
   address, other than knowing it is that of a DHCPv6 relay agent on the
   client LAN segment.  DHCPv6 Packets relayed to the client are sourced
   by the relay using this relay's IPv6 address, which could be a link
   local address.

   The Client SHOULD refresh assigned route information periodically.
   The generic DHCPv6 Information Refresh Time Option, as specified in
   [RFC4242], can be used when it is desired for the client to
   periodically refresh of route information.

   The routes conveyed by the Route Option should be considered as
   complimentary to any other static route learning and maintenance
   mechanism used by, or on the client with one modification: The client
   MUST flush DHCPv6 installed routes following a link flap event on the
   DHCPv6 client interface over which the routes were installed.  This
   requirement is necessary to automate the flushing of routes for
   clients that may move to a different network.

   Client MUST confirm that routers announced over DHCPv6 are reachable,
   using one of methods suitable for specific network type.  The most
   common mechanism is Neighbor Unreachability Detection (NUD),
   specified in [RFC4861].  Client SHOULD use NUD to verify that
   received routers are reachable before adjusting its routing tables.
   Client MAY use other reachability verification mechanisms specific to
   used network technology.  To avoid potential long-lived routing black
   holes, client MAY periodically confirm that router is still
   reachable.

5.1.  Conflict resolution

   Information received via Route Options over DHCPv6 MUST be treated
   equally to routing information obtained via other sources.  In
   particular, from the RA perspective, DHCPv6 provisioning should be
   treated as if yet another RA was received.  Preference field should
   be taken into consideration during route information processing.  In
   particular, administrators are encouraged to read [RFC4191],
   Section 4.1 for guidance.

   To facilitate information merge between DHCPv6 and RA, DHCPv6 options
   in this document convey the same information specified in
   [I-D.sarikaya-6man-next-hop-ra].






Sarikaya                Expires December 22, 2014              [Page 12]


Internet-Draft                                                 June 2014


   To facilitate information merge between DHCPv6 and RA, DHCPv6 option
   RT_PREFIX conveys the same information specified in [RFC4191]  albeit
   on-wire format is slightly different.  The differences are:

   Metric field is an 8-bit field that conveys the route metric.

   RIO uses 128-length prefix field, while DHCPv6 option uses variable
   prefix length.  That difference is used to minimize packet size as it
   avoid transmitting zeroed octets.  Despite slightly different
   encoding, delivered information is exactly the same.

   If prefix is available directly on-link, Route Prefix option is
   conveyed directly in DHCPv6 message, not within Next Hop option.
   That feature is considered a superset, compared to RIO.

   In short, when DHCPv6 RT_PREFIX option is used alone this
   specification works in compatibility mode with [RFC4191].

6.  IANA Considerations

   IANA is kindly requested to allocate DHCPv6 option code TBD1 to the
   OPTION_NEXT_HOP, TBD2 to OPTION_RT_PREFIX, TBD3 to OPTION_SOURCE_AP.
   All values should be added to the DHCPv6 option code space defined in
   Section 24.3 of [RFC3315].

7.  Security Considerations

   The overall security considerations discussed in [RFC3315] apply also
   to this document.  The Route option could be used by malicious
   parties to misdirect traffic sent by the client either as part of a
   denial of service or man-in-the-middle attack.  An alternative denial
   of service attack could also be realized by means of using the route
   option to overflowing any known memory limitations of the client, or
   to exceed the client's ability to handle the number of next hop
   addresses.

   Neither of the above considerations are new and specific to the
   proposed route option.  The mechanisms identified for securing DHCPv6
   as well as reasonable checks performed by client implementations are
   deemed sufficient in addressing these problems.

   It is essential that clients verify that announced routers are indeed
   reachable, as specified in Section 5.  Failing to do so may create
   black hole routing problem.

   This mechanism may introduce severe problems if deployed in networks
   that use dynamic routing protocols.  See Section 2.6 for details.




Sarikaya                Expires December 22, 2014              [Page 13]


Internet-Draft                                                 June 2014


   DHCPv6 becomes a complete provisioning protocol with this mechanism,
   i.e. all necessary configuration parameters may be delivered using
   DHCPv6 only.  It was suggested that in some cases this may lead to
   decision of disabling RA.  While RA-less networks could offer lower
   operational expenses and protection against rogue RAs, they would not
   work with nodes that do not support this feature.  Therefore such
   decision is not recommended, unless all effects are carefully
   analyzed.  It is worth noting that disabling RA support in hosts
   would solve rogue RA problem, it would in fact only change the issue
   into rogue DHCPv6 problem.  That is somewhat beneficial, however, as
   rogue RA may affect all nodes immediately while rogue DHCPv6 server
   will affect only new nodes, that boot up after rogue server manifests
   itself.

   Reader is also encouraged to read DHCPv6 security considerations
   document [I-D.ietf-dhc-sedhcpv6].

8.  Acknowledgements

   The author acknowledges the work done by his co-authors in MIF WG
   draft entitled DHCPv6 Route Options.

9.  References

9.1.  Normative References

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

   [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.

9.2.  Informative References

   [I-D.ietf-dhc-sedhcpv6]
              Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure
              DHCPv6 with Public Key", draft-ietf-dhc-sedhcpv6-03 (work
              in progress), June 2014.

   [I-D.ietf-mif-mpvd-arch]
              Anipko, D., "Multiple Provisioning Domain Architecture",
              draft-ietf-mif-mpvd-arch-01 (work in progress), May 2014.




Sarikaya                Expires December 22, 2014              [Page 14]


Internet-Draft                                                 June 2014


   [I-D.sarikaya-6man-next-hop-ra]
              Sarikaya, B., "IPv6 RA Options for Next Hop Routes",
              draft-sarikaya-6man-next-hop-ra-02 (work in progress),
              June 2014.

   [RFC3442]  Lemon, T., Cheshire, S., and B. Volz, "The Classless
              Static Route Option for Dynamic Host Configuration
              Protocol (DHCP) version 4", RFC 3442, December 2002.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4242]  Venaas, S., Chown, T., and B. Volz, "Information Refresh
              Time Option for Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 4242, November 2005.

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

   [RFC6204]  Singh, H., Beebee, W., Donley, C., Stark, B., and O.
              Troan, "Basic Requirements for IPv6 Customer Edge
              Routers", RFC 6204, April 2011.

   [RFC7157]  Troan, O., Miles, D., Matsushima, S., Okimoto, T., and D.
              Wing, "IPv6 Multihoming without Network Address
              Translation", RFC 7157, March 2014.

Author's Address

   Behcet Sarikaya
   Huawei USA
   5340 Legacy Dr.
   Plano, TX  75024
   United States

   Phone: +1 972-509-5599
   Email: sarikaya@ieee.org













Sarikaya                Expires December 22, 2014              [Page 15]