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Versions: (draft-stenberg-homenet-hncp) 00 01 02 03 04 05 06 07 08 09 10 RFC 7788

Homenet Working Group                                        M. Stenberg
Internet-Draft
Intended status: Standards Track                                S. Barth
Expires: July 10, 2015
                                                              P. Pfister
                                                           Cisco Systems
                                                         January 6, 2015


                    Home Networking Control Protocol
                       draft-ietf-homenet-hncp-03

Abstract

   This document describes the Home Networking Control Protocol (HNCP),
   an extensible configuration protocol and a set of requirements for
   home network devices on top of the Distributed Node Consensus
   Protocol (DNCP).  It enables automated configuration of addresses,
   naming, network borders and the seamless use of a routing protocol.

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 July 10, 2015.

Copyright Notice

   Copyright (c) 2015 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   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.  Requirements language . . . . . . . . . . . . . . . . . . . .   3
   3.  DNCP Profile  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Adjacent Links  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Border Discovery  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Autonomic Address Configuration . . . . . . . . . . . . . . .   6
     6.1.  External Connections  . . . . . . . . . . . . . . . . . .   7
       6.1.1.  External Connection TLV . . . . . . . . . . . . . . .   7
       6.1.2.  Delegated Prefix TLV  . . . . . . . . . . . . . . . .   7
       6.1.3.  DHCP Data TLVs  . . . . . . . . . . . . . . . . . . .   8
     6.2.  Prefix Assignment . . . . . . . . . . . . . . . . . . . .   9
       6.2.1.  Assigned Prefix TLV . . . . . . . . . . . . . . . . .   9
       6.2.2.  Prefix Assignment Algorithm Parameters  . . . . . . .  10
       6.2.3.  Making New Assignments  . . . . . . . . . . . . . . .  12
       6.2.4.  Applying Assignments  . . . . . . . . . . . . . . . .  12
       6.2.5.  DHCPv6-PD Excluded Prefix Support . . . . . . . . . .  13
       6.2.6.  Downstream Prefix Delegation Support  . . . . . . . .  13
     6.3.  Node Address Assignment . . . . . . . . . . . . . . . . .  13
     6.4.  Local IPv4 and ULA Prefixes . . . . . . . . . . . . . . .  14
   7.  Configuration of Hosts and non-HNCP Routers . . . . . . . . .  15
     7.1.  DHCPv6 for Addressing or Configuration  . . . . . . . . .  15
     7.2.  Sending Router Advertisements . . . . . . . . . . . . . .  16
     7.3.  DHCPv6 for Prefix Delegation  . . . . . . . . . . . . . .  17
     7.4.  DHCPv4 for Adressing and Configuration  . . . . . . . . .  17
     7.5.  Multicast DNS Proxy . . . . . . . . . . . . . . . . . . .  17
   8.  Naming and Service Discovery  . . . . . . . . . . . . . . . .  18
     8.1.  DNS Delegated Zone TLV  . . . . . . . . . . . . . . . . .  18
     8.2.  Domain Name TLV . . . . . . . . . . . . . . . . . . . . .  19
     8.3.  Node Name TLV . . . . . . . . . . . . . . . . . . . . . .  20
   9.  Securing Third-Party Protocols  . . . . . . . . . . . . . . .  20
   10. HNCP Versioning and Capabilities  . . . . . . . . . . . . . .  21
   11. Requirements for HNCP Routers . . . . . . . . . . . . . . . .  22
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  23
     12.1.  Border Determination . . . . . . . . . . . . . . . . . .  24
     12.2.  Security of Unicast Traffic  . . . . . . . . . . . . . .  24
     12.3.  Other Protocols in the Home  . . . . . . . . . . . . . .  25
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     14.1.  Normative references . . . . . . . . . . . . . . . . . .  26
     14.2.  Informative references . . . . . . . . . . . . . . . . .  26
   Appendix A.  Changelog  . . . . . . . . . . . . . . . . . . . . .  28
   Appendix B.  Draft source . . . . . . . . . . . . . . . . . . . .  28



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   Appendix C.  Implementation . . . . . . . . . . . . . . . . . . .  28
   Appendix D.  Acknowledgements . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   HNCP synchronizes state across a small site in order to allow
   automated network configuration.  The protocol enables use of border
   discovery, address prefix distribution
   [I-D.ietf-homenet-prefix-assignment], naming and other services
   across multiple links.

   HNCP provides enough information for a routing protocol to operate
   without homenet-specific extensions.  In homenet environments where
   multiple IPv6 source-prefixes can be present, routing based on source
   and destination address is necessary [RFC7368].

2.  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].

3.  DNCP Profile

   HNCP is defined as a profile of DNCP [I-D.ietf-homenet-dncp] with the
   following parameters:

   o  HNCP uses UDP datagrams on port HNCP-UDP-PORT as a transport over
      link-local scoped IPv6, using unicast and multicast (group All-
      Homenet-Routers).  Received datagrams with an IPv6 source or
      destination address which is not link-local scoped MUST be
      ignored.

   o  HNCP operates on multicast-capable interfaces only, thus every
      DNCP Connection Identifier MUST refer to one, except for the value
      0 which is reserved for internal purposes and MUST NOT be used for
      connection enumeration.  Implementations MAY use a value
      equivalent to the sin6_scope_id for the given interface.

   o  HNCP unicast messages SHOULD be secured using DTLS [RFC6347] as
      described in DNCP if exchanged over unsecured links.  UDP on port
      HNCP-DTLS-PORT is used for this purpose.  A node implementing the
      security mechanism MUST support the DNCP Pre-Shared Key method,
      SHOULD support the DNCP Certificate Based Trust Consensus and MAY
      support the PKI-based trust method.





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   o  HNCP uses opaque 32-bit node identifiers
      (DNCP_NODE_IDENTIFIER_LENGTH = 32).  A node implementing HNCP
      SHOULD generate and use a random node identifier.  If it receives
      a Node State TLV with the same node identifier and a higher update
      sequence number, it MUST immediately generate and use a new random
      node identifier which is not used by any other node.

   o  HNCP nodes MUST treat all Long Network State Update messages
      received via multicast on a link which has DNCP security enabled
      as if they were Short Network State Update messages, i.e. they
      MUST ignore all contained Node State TLVs.

   o  HNCP nodes use the following Trickle parameters:

      *  k SHOULD be 1, given the timer reset on data updates and
         retransmissions should handle packet loss.

      *  Imin SHOULD be 200 milliseconds but MUST NOT be lower.  Note:
         Earliest transmissions may occur at Imin / 2.

      *  Imax SHOULD be 7 doublings of Imin (i.e. 25.6 seconds) but MUST
         NOT be lower.

   o  HNCP nodes MUST use the leading 64 bits of MD5 [RFC1321] as DNCP
      non-cryptographic hash function H(x).

   o  HNCP nodes MUST use the keep-alive extension on all connections.
      The default keep-alive interval (DNCP_KEEPALIVE_INTERVAL) is 20
      seconds, the multiplier (DNCP_KEEPALIVE_MULTIPLIER) MUST be 2.1,
      the grace-interval (DNCP_GRACE_INTERVAL) SHOULD be equal to
      DNCP_KEEPALIVE_MULTIPLIER times DNCP_KEEPALIVE_INTERVAL.

4.  Adjacent Links

   HNCP uses the concept of Adjacent Links for some of its applications.
   This term is defined as follows:

   If the connection of a node is detected or configured to be an ad-hoc
   interface the Adjacent Link only consists of said interface.

   Otherwise the Adjacent Link contains all interfaces bidirectionally
   reachable from a given local interface.  An interface X of a node A
   and an interface Y of a node B are bidirectionally reachable if and
   only if node A publishes a Neighbor TLV with the Neighbor Node
   Identifier B, the Neighbor Connection Identifier Y and the Local
   Connection Identifier X and node B publishes a Neighbor TLV with the
   Neighbor Node Identifier A, a Neighbor Connection Identifier X and
   the Local Connection Identifier Y.  In addition a node MUST be able



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   to detect whether two of its local interfaces belong to the same
   Adjacent Link either by local means or by inferring that from the
   bidirectional reachability between two different local interfaces and
   the same remote interface.

5.  Border Discovery

   HNCP associates each HNCP interface with a category (e.g., internal
   or external).  This section defines the border discovery algorithm
   derived from the edge router interactions described in the Basic
   Requirements for IPv6 Customer Edge Routers [RFC7084].  This
   algorithm is suitable for both IPv4 and IPv6 (single or dual-stack)
   and determines whether an HNCP interface is internal, external, or
   uses another fixed category.  This algorithm MUST be implemented by
   any router implementing HNCP.

   In order to avoid conflicts between border discovery and homenet
   routers running DHCPv4 [RFC2131] or DHCPv6-PD [RFC3633] servers, each
   router MUST implement the following mechanism based on The User Class
   Option for DHCPv4 [RFC3004] and its DHCPv6 counterpart [RFC3315]:

   o  An HNCP router running a DHCP client on a homenet interface MUST
      include a DHCP User-Class consisting of the ASCII-String
      "HOMENET".

   o  An HNCP router running a DHCP server on a homenet interface MUST
      ignore or reject DHCP-Requests containing a DHCP User-Class
      consisting of the ASCII-String "HOMENET".

   The border discovery auto-detection algorithm works as follows, with
   evaluation stopping at first match:

   1.  If a fixed category is configured for the interface, it MUST be
       used.

   2.  If a delegated prefix could be acquired by running a DHCPv6
       client on the interface, it MUST be considered external.

   3.  If an IPv4 address could be acquired by running a DHCPv4 client
       on the interface it MUST be considered external.

   4.  Otherwise the interface MUST be considered internal.

   A router MUST allow setting a category of either auto-detected,
   internal or external for each interface which is suitable for both
   internal and external connections.  In addition the following
   specializations of the internal category are defined to modify the
   local router behavior:



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   Leaf category:  This declares an interface used by client devices
      only.  A router MUST consider such interface as internal but MUST
      NOT send nor receive HNCP messages on such interface.  A router
      SHOULD implement this category.

   Guest category:  This declares an interface used by untrusted client
      devices only.  In addition to the restrictions of the Leaf
      category, connected devices MUST NOT be able to reach other
      devices inside the HNCP network nor query services advertised by
      them unless explicitly allowed, instead they SHOULD only be able
      to reach the internet.  This category SHOULD be supported.

   Ad-hoc category:  This configures an interface to be ad-hoc
      (Section 4) and MAY be implemented.

   Hybrid category:  This declares an interface to be internal while
      still using external connections on it.  It is assumed that the
      link is under control of a legacy, trustworthy non-HNCP router,
      still within the same network.  Detection of this category
      automatically in addition to manual configuration is out of scope
      for this document.  This category MAY be implemented.

   Each router MUST continuously scan each active interface that does
   not have a fixed category in order to dynamically reclassify it if
   necessary.  The router therefore runs an appropriately configured
   DHCPv4 and DHCPv6 client as long as the interface is active including
   states where it considers the interface to be internal.  The router
   SHOULD wait for a reasonable time period (5 seconds as a default),
   during which the DHCP clients can acquire a lease, before treating a
   newly activated or previously external interface as internal.  Once
   it treats a certain interface as internal it MUST start forwarding
   traffic with appropriate source addresses between its internal
   interfaces and allow internal traffic to reach external networks
   according to the routes it publishes.  Once a router detects an
   interface transitioning to external it MUST stop any previously
   enabled internal forwarding.  In addition it SHOULD announce the
   acquired information for use in the network as described in later
   sections of this draft if the interface appears to be connected to an
   external network.

6.  Autonomic Address Configuration

   This section specifies how HNCP routers configure host and router
   addresses.  At first border routers share information obtained from
   service providers or local configuration by publishing one or more
   External Connection TLVs.  These contain other TLVs such as Delegated
   Prefix TLVs which are then used for prefix assignment.  Finally, HNCP
   routers obtain addresses using a stateless (SLAAC-like) procedure or



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   a specific stateful mechanism and hosts and legacy routers are
   configured using SLAAC or DHCP.

   In all TLVs specified in this section which include a prefix, IPv4
   prefixes are encoded using the IPv4-mapped IPv6 addresses format
   [RFC4291].  The prefix length of such prefix is set to 96 plus the
   IPv4 prefix length.

6.1.  External Connections

   Each HNCP router MAY obtain external connection information from one
   or more sources, e.g.  DHCPv6-PD [RFC3633], NETCONF [RFC6241] or
   static configuration.  This section specifies how such information is
   encoded and advertised.

6.1.1.  External Connection TLV

   An External Connection TLV is a container-TLV used to gather network
   configuration information associated with a single external
   connection.  A node MAY publish zero, one or more instances of this
   TLV.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type: EXTERNAL-CONNECTION (33)|          Length: > 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Nested TLVs                          |

   The External Connection TLV is a container which:

   o  MAY contain zero, one or more Delegated Prefix TLVs.

   o  MUST NOT contain multiple Delegated Prefix TLVs with the same
      prefix.  In such a situation, the container MUST be ignored.

   o  MAY contain at most one DHCPv6 Data TLV and at most one DHCPv4
      Data TLV encoding options associated with the External Connection
      but MUST NOT contain more than one of each otherwise the whole
      External Connection TLV MUST be ignored.

   o  MAY contain other TLVs for future use.

6.1.2.  Delegated Prefix TLV

   The Delegated Prefix TLV is used by HNCP routers to advertise
   prefixes which are allocated to the whole network and will be used




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   for prefix assignment.  All Delegated Prefix TLVs MUST be nested in
   an External Connection TLV.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type: DELEGATED-PREFIX (34)  |          Length: >= 9         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Valid Lifetime                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Preferred Lifetime                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Prefix Length |                                               |
   +-+-+-+-+-+-+-+-+            Prefix [+ nested TLVs]             +
   |                                                               |

   Valid Lifetime:   The time in seconds the delegated prefix is valid.
      The value is relative to the point in time the Node-Data TLV was
      last published.  It MUST be updated whenever the node republishes
      its Node-Data TLV.

   Preferred Lifetime:   The time in seconds the delegated prefix is
      preferred.  The value is relative to the point in time the Node-
      Data TLV was last published.  It MUST be updated whenever the node
      republishes its Node-Data TLV.

   Prefix Length:   The number of significant bits in the Prefix.

   Prefix:   Significant bits of the prefix padded with zeroes up to the
      next byte boundary.

   Nested TLVs:  Other TLVs included in the Delegated Prefix TLV and
      starting at the next 32 bits boundary following the end of the
      encoded prefix.

         If the encoded prefix represents an IPv6 prefix, at most one
         DHCPv6 Data TLV MAY be included.

         If the encoded prefix represents an IPv4-mapped IPv6 address,
         at most one DHCPv4 Data TLV MAY be included.

         It MAY contain other TLVs for future use.

6.1.3.  DHCP Data TLVs

   Auxiliary connectivity information is encoded as a stream of DHCP
   options.  Such TLVs MUST only be present in an External Connection
   TLV or a Delegated Prefix TLV.  When included in an External



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   Connection TLV, they MUST contain DHCP options which are relevant to
   the whole External Connection.  When included in a Delegated Prefix,
   they MUST contain DHCP options which are specific to the Delegated
   Prefix.

   The DHCPv6 Data TLV uses the following format:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: DHCPV6-DATA (37)     |          Length: > 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      DHCPv6 option stream                     |

   DHCPv6 option stream:   DHCPv6 options encoded as specified in
      [RFC3315].

   The DHCPv4 Data TLV uses the following format:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type: DHCPV4-DATA (38)    |          Length: > 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       DHCPv4 option stream                    |

   DHCPv4 option stream:   DHCPv4 options encoded as specified in
      [RFC2131].

6.2.  Prefix Assignment

   HNCP uses the Distributed Prefix Assignment Algorithm specified in
   [I-D.ietf-homenet-prefix-assignment] in order to assign prefixes to
   HNCP internal links and uses the terminology defined there.

6.2.1.  Assigned Prefix TLV

   Published Assigned Prefixes MUST be advertised using the Assigned
   Prefix TLV:












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   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type: ASSIGNED-PREFIX (35)   |          Length: >= 6         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Connection Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Rsv. | Prty. | Prefix Length |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+            Prefix             +
   |                                                               |

   Connection Identifier:   The DNCP Connection Identifier of the link
      the prefix is assigned to, or 0 if the link is a Private Link.

   Rsv.:   Bits reserved for future use.  MUST be set to zero when
      creating this TLV and ignored when parsing it.

   Prty:   The Advertised Prefix Priority from 0 to 15.

      0-1  :  Low priorities.

      2    :  Default priority.

      3-7  :  High priorities.

      8-11 :  Administrative priorities.  MUST NOT be used unless
         specified in the router's configuration.

      12-14:  Reserved for future use.

      15   :  Provider priorities.  MAY only be used by the router
         advertising the corresponding delegated prefix and based on
         static or dynamic configuration (e.g., for excluding a prefix
         based on DHCPv6-PD Prefix Exclude Option [RFC6603]).

   Prefix Length:   The number of significant bits in the Prefix field.

   Prefix:   The significant bits of the prefix padded with zeroes up to
      the next byte boundary.

6.2.2.  Prefix Assignment Algorithm Parameters

   All HNCP nodes running the prefix assignment algorithm MUST use the
   following parameters:

   Node IDs:   DNCP Node Identifiers are used.  The comparison operation
      is defined as bit-wise comparison.




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   Set of Delegated Prefixes:   The set of prefixes encoded in Delegated
      Prefix TLVs which are not strictly included in prefixes encoded in
      other Delegated Prefix TLVs.  Note that Delegated Prefix TLVs
      included in ignored External Connection TLVs are not considered.
      It is dynamically updated as Delegated Prefix TLVs are added or
      removed.

   Set of Shared Links:   The set of HNCP internal, leaf, guest or
      hybrid links.  It is dynamically updated as HNCP links are added,
      removed, become internal or cease to be.

   Set of Private Links:   This document defines Private Links
      representing DHCPv6-PD clients or as a mean to advertise prefixes
      included in the DHCPv6 Exclude Prefix option.  Other
      implementation-specific Private Links may exist.

   Set of Advertised Prefixes:   The set of prefixes included in
      Assigned Prefix TLVs advertised by other HNCP routers.  The
      associated Advertised Prefix Priority is the priority specified in
      the TLV.  The associated Shared Link is determined as follows:

      *  If the Link Identifier is zero, the Advertised Prefix is not
         assigned on a Shared Link.

      *  If the Link Identifier is not zero the Shared Link is equal to
         the Adjacent Link (Section 4).  Advertised Prefixes as well as
         their associated priorities and associated Shared Links MUST be
         updated as Assigned Prefix TLVs or Neighbor TLVs are added,
         removed or updated.

   ADOPT_MAX_DELAY:   The default value is 0 seconds (i.e. prefix
      adoption MAY be done instantly).

   BACKOFF_MAX_DELAY:   The default value is 4 seconds.

   RANDOM_SET_SIZE:   The default value is 64.

   Flooding Delay:   The default value is 5 seconds.

   Default Advertised Prefix Priority:   When a new assignment is
      created or an assignment is adopted - as specified in the prefix
      assignment algorithm routine - the default Advertised Prefix
      Priority to be used is 2.








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6.2.3.  Making New Assignments

   Whenever the Prefix Assignment Algorithm routine is run on an
   Adjacent Link and whenever a new prefix may be assigned (case 1 of
   the routine), the decision of whether the assignment of a new prefix
   is desired MUST follow these rules:

      If the Delegated Prefix TLV contains a DHCPv4 or DHCPv6 Data TLV,
      and the meaning of one of the DHCP options is not understood by
      the HNCP router, the creation of a new prefix is not desired.

      If the remaining preferred lifetime of the prefix is 0 and there
      is another delegated prefix of the same IP version used for prefix
      assignment with a non-null preferred lifetime, the creation of a
      new prefix is not desired.

      Otherwise, the creation of a new prefix is desired.

   If the considered delegated prefix is an IPv6 prefix, and whenever
   there is at least one available prefix of length 64, a prefix of
   length 64 MUST be selected unless configured otherwise by an
   administrator.  In case no prefix of length 64 would be available, a
   longer prefix MAY be selected.

   If the considered delegated prefix is an IPv4 prefix ( Section 6.4
   details how IPv4 delegated prefixes are generated), a prefix of
   length 24 SHOULD be preferred.

   In any case, a router MUST support a mechanism suitable to distribute
   addresses from the considered prefix to clients on the link.
   Otherwise it MUST NOT create or adopt it, i.e. a router assigning an
   IPv4 prefix MUST support the L-capability and a router assigning an
   IPv6 prefix not suitable for stateless autoconfiguration MUST support
   the H-capability as defined in Section 10.

6.2.4.  Applying Assignments

   The prefix assignment algorithm indicates when a prefix is applied to
   the respective Adjacent Link.  When that happens each router
   connected to said link:

      MUST create an appropriate on-link route for said prefix and
      advertise it using the chosen routing protocol.

      MUST participate in the client configuration election as described
      in Section 7.





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      MAY add an address from said prefix to the respective network
      interface as described in Section 6.3.

6.2.5.  DHCPv6-PD Excluded Prefix Support

   Whenever a DHCPv6 Prefix Exclude option [RFC6603] is received with a
   delegated prefix, the excluded prefix MUST be advertised as assigned
   to a Private Link with the maximum priority (i.e. 15).

   The same procedure MAY be applied in order to exclude prefixes
   obtained by other means of configuration.

6.2.6.  Downstream Prefix Delegation Support

   When an HNCP router receives a request for prefix delegation, it
   SHOULD assign one prefix per delegated prefix, wait for them to be
   applied, and delegate them to the client.  Such assignment MUST be
   done in accordance with the Prefix Assignment Algorithm.  Each client
   MUST be considered as an independent Private Link and delegation MUST
   be based on the same set of Delegated Prefixes.

   The assigned prefixes MUST NOT be given to clients before they are
   applied, and MUST be withdrawn whenever they are destroyed.  As an
   exception to this rule a router MAY prematurely give out a prefix
   which is advertised but not yet applied if it does so with a valid
   lifetime of not more than 30 seconds and ensures removal or
   correction of lifetimes as soon as possible to shorten delays of
   processed requests.

6.3.  Node Address Assignment

   This section specifies how HNCP nodes reserve addresses for their own
   use.  Nodes MAY, at any time, try to reserve a new address.  SLAAC
   SHOULD be used whenever possible.  The following method MUST be used
   otherwise.

   For any IPv6 prefix longer than 64 bits (resp. any IPv4 prefix)
   assigned to an Adjacent Link, the first quarter of the addresses are
   reserved for routers HNCP based assignments, whereas the last three
   quarters are left to the DHCPv6 (resp.  DHCPv4) elected router
   (Section 10 specifies the DHCP server election process).  For
   instance, if the prefix 192.0.2.0/24 is assigned and applied to an
   Adjacent Link, addresses included in 192.0.2.0/26 are reserved for
   HNCP nodes and the remaining addresses are reserved for the elected
   DHCPv4 server.

   HNCP routers assign themselves addresses using the Node Address TLV:




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   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: NODE-ADDRESS (36)    |           Length: 20          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Connection Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                           IP Address                          |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Connection Identifier:   The DNCP Connection Identifier of the link
      the address is assigned to, or 0 if it is not assigned on an HNCP
      enabled link.

   IP Address:   The IPv6 address, or the IPv4 address encoded as an
      IPv4-mapped IPv6 address [RFC4291].

   The process of obtaining addresses is specified as follows:

   o  A router MUST NOT start advertising an address if it is already
      advertised by another router.

   o  An assigned address MUST be in the first quarter of an assigned
      prefix currently applied on the specified link.

   o  An address MUST NOT be used unless it has been advertised for at
      least ADDRESS_APPLY_DELAY consecutive seconds, and is still
      currently being advertised.  The default value for
      ADDRESS_APPLY_DELAY is 3 seconds.

   o  Whenever the same address is advertised by more than one node all
      but the one advertised by the node with the highest node
      identifier MUST be removed.

6.4.  Local IPv4 and ULA Prefixes

   HNCP routers can create an ULA or private IPv4 prefix to enable
   connectivity between local devices.  These prefixes are inserted in
   HNCP as if they were delegated prefixes.  The following rules apply:

      An HNCP router SHOULD create an ULA prefix if there is no other
      non-deprecated IPv6 prefix in the network.  It MAY also do so if
      there are other delegated IPv6 prefixes but none of which is a
      non-deprecated ULA but MUST NOT do so otherwise.  Whenever it
      detects another non-deprecated ULA being advertised it MUST cease



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      to announce its locally generated one.  It MAY also do so once it
      detects a non-deprecated non-ULA IPv6 delegated prefix.

      An HNCP router MUST create a non-deprecated private IPv4 prefix
      [RFC1918] whenever it wishes to provide external IPv4 connectivity
      to the network and no other non-deprecated private IPv4 prefix
      currently exists.  It MAY also create a deprecated private IPv4
      prefix if no IPv4 prefix exists and it wants to enable local IPv4
      connectivity but MUST NOT do so otherwise.  In case multiple IPv4
      prefixes are announced all but one MUST be removed while non-
      deprecated ones take precedence over deprecated ones and
      announcements by nodes with a higher node identifier take
      precedence over those with a lower one.  The router publishing the
      non-deprecated prefix MUST announce an IPv4 default route using
      the routing protocol and perform NAT on behalf of the network as
      long as it publishes the prefix, other routers in the network MUST
      NOT.

   Creation of such ULA and IPv4 prefixes MUST be delayed by a random
   timespan between 0 and 10 seconds in which the router MUST scan for
   other nodes trying to do the same.

   When a new ULA prefix is created, the prefix is selected based on the
   configuration, using the last non-deprecated ULA prefix, or generated
   based on [RFC4193].

7.  Configuration of Hosts and non-HNCP Routers

   HNCP routers need to ensure that hosts and non-HNCP downstream
   routers on internal links are configured with addresses and routes.
   Since DHCP-clients can usually only bind to one server at a time an
   election takes place.

   HNCP routers may have different capabilities for configuring
   downstream devices and providing naming services.  Each router MUST
   therefore indicate its capabilities as specified in Section 10 in
   order to participate as a candidate in the election.

7.1.  DHCPv6 for Addressing or Configuration

   In general stateless address configuration is preferred whenever
   possible since it enables fast renumbering and low overhead, however
   stateful DHCPv6 can be useful in addition to collect hostnames and
   use them to provide naming services or if stateless configuration is
   not possible for the assigned prefix length.

   The designated stateful DHCPv6 server for a link is elected based on
   the capabilities described in Section 10.  The winner is the router



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   connected to the Adjacent Link (Section 4) advertising the greatest
   H-capability.  In case of a tie, Capability Values and node
   identifiers are considered (greatest value is elected).  The elected
   router MUST serve stateful DHCPv6 and Router Advertisements on the
   given link.  Furthermore it MUST provide naming services for acquired
   hostnames as outlined in Section 8.  Stateful addresses being handed
   out SHOULD have a low preferred lifetime (e.g. 1s) to not hinder fast
   renumbering if either the DHCPv6 server or client do not support the
   DHCPv6 reconfigure mechanism and the address is from a prefix for
   which stateless autoconfiguration is supported as well.  In case no
   router was elected, stateful DHCPv6 is not provided and each router
   assigning IPv6 prefixes on said link MUST serve Router Advertisements
   and stateless DHCPv6.

7.2.  Sending Router Advertisements

   The HNCP router being elected as DHCPv6 server for addressing or
   configuration MUST send Router Advertisements periodically via
   multicast and via unicast in response to Router Solicitations.  In
   addition other routers on the link MAY announce Router
   Advertisements.  This might result in a more optimal routing decision
   for clients.  The following rules MUST be followed when sending
   Router Advertisements:

      The "Managed address configuration" flag MUST be set whenever a
      router connected to the link is advertising a non-null
      H-capability and MUST NOT be set otherwise.  The "Other
      configuration" flag MUST always be set.

      The default Router Lifetime MUST be set to an appropriate non-null
      value whenever an IPv6 default route is known in the HNCP network
      and MUST be set to zero otherwise.

      A Prefix Information Option MUST be added for each assigned and
      applied IPv6 prefix on the given link.  The autonomous address-
      configuration flag MUST be set whenever the prefix is suitable for
      stateless configuration.  The preferred and valid lifetimes MUST
      be smaller than the preferred and valid lifetimes of the delegated
      prefix the prefix is from.  When a prefix is removed, it MUST be
      deprecated as specified in [RFC7084].

      A Route Information Option [RFC4191] MUST be added for each
      delegated IPv6 prefix known in the HNCP network.  Additional ones
      SHOULD be added for each non-default IPv6 route with an external
      destination advertised by the routing protocol.

      A Recursive DNS Server Option and a DNS Search List Option MUST be
      included with appropriate contents.



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      To allow for optimized routing decisions for clients on the local
      link routers SHOULD adjust their Default Router Preference and
      Route Preferences [RFC4191] so that the priority is set to low if
      the next hop of the default or more specific route is on the same
      interface as the Route Advertisement being sent on.  Similarly the
      router MAY use the high priority if it is certain it has the best
      metric of all routers on the link for all routes known in the
      network with the respective destination.

   Every router sending Router Advertisements MUST immediately send an
   updated Router Advertisement via multicast as soon as it notices a
   condition resulting in a change of any advertised information.

7.3.  DHCPv6 for Prefix Delegation

   The designated DHCPv6 server for prefix-delegation on a link is
   elected based on the capabilities described in Section 10.  The
   winner is the router connected to the Adjacent Link (Section 4)
   advertising the greatest P-capability.  In case of a tie, Capability
   Values and Node Identifiers are considered (greatest value is
   elected).  The elected router MUST provide prefix-delegation services
   [RFC3633] on the given link and follow the rules in Section 6.2.6.

7.4.  DHCPv4 for Adressing and Configuration

   The designated DHCPv4 server on a link is elected based on the
   capabilities described in Section 10.  The winner is the router
   connected to the Adjacent Link (Section 4) advertising the greatest
   L-capability.  In case of a tie, Capability Values and node
   identifiers are considered (greatest value is elected).  The elected
   router MUST provide DHCPv4 services on the given link.

   The DHCPv4 serving router MUST announce itself as router [RFC2132] to
   clients if and only if there is an IPv4 default route known in the
   network.  In addition the router SHOULD announce a Classless Static
   Route Option [RFC3442] for each non-default IPv4 route advertised in
   the routing protocol with an external destination.

   DHCPv4 lease times SHOULD be short (i.e. not longer than 5 minutes)
   in order to provide reasonable response times to changes.

7.5.  Multicast DNS Proxy

   The designated MDNS [RFC6762]-proxy on a link is elected based on the
   capabilities described in Section 10.  The winner is the router with
   the highest Node Identifier among those with the highest Capability
   Value on the link that support the M-capability.  The elected router




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   MUST provide an MDNS-proxy on the given link and announce it as
   described in Section 8.

8.  Naming and Service Discovery

   Network-wide naming and service discovery can greatly improve the
   user-friendliness of an IPv6 network.  The following mechanism
   provides means to setup and delegate naming and service discovery
   across multiple HNCP routers.

   Each HNCP router SHOULD provide and announce an auto-generated or
   user-configured name for each internal Adjacent Link (Section 4) for
   which it is the designated DHCPv4, stateful DHCPv6 server or MDNS
   [RFC6762]-proxy and for which it provides DNS-services on behalf of
   devices on said link.  In addition it MAY provide reverse lookup
   services.

   The following TLVs are defined and MUST be supported by all nodes
   implementing naming and service discovery:

8.1.  DNS Delegated Zone TLV

   This TLV is used to announce a forward or reverse DNS zone delegation
   in the HNCP network.  Its meaning is roughly equivalent to specifying
   an NS and A/AAAA record for said zone.  There MUST NOT be more than
   one delegation for the same zone in the whole DNCP network.  In case
   of a conflict the announcement of the node with the highest node
   identifier takes precedence and all other nodes MUST cease to
   announce the conflicting TLV.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type: DNS-DELEGATED-ZONE (39) |        Length: >= 17          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                           IP Address                          |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |reserved |L|B|S|                                               |
   +-+-+-+-+-+-+-+-+  Zone (DNS label sequence - variable length)  |
   |                                                               |

      IP Address is the IPv6 address of the authoritative DNS server for
      the zone; IPv4 addresses are represented as IPv4-mapped addresses
      [RFC4291].  The special value of :: (all-zero) means the
      delegation is available in the global DNS-hierarchy.



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      reserved bits MUST be zero when creating and ignored when parsing
      this TLV.

      L-bit (DNS-SD [RFC6763] Legacy-Browse) indicates that this
      delegated zone should be included in the network's DNS-SD legacy
      browse list of domains at lb._dns- sd._udp.(DOMAIN-NAME).  Local
      forward zones SHOULD have this bit set, reverse zones SHOULD NOT.

      B-bit (DNS-SD [RFC6763] Browse) indicates that this delegated zone
      should be included in the network's DNS-SD browse list of domains
      at b._dns-sd._udp.  (DOMAIN-NAME).  Local forward zones SHOULD
      have this bit set, reverse zones SHOULD NOT.

      S-bit (fully-qualified DNS-SD [RFC6763] -domain) indicates that
      this delegated zone consists of a fully-qualified DNS-SD domain,
      which should be used as base for DNS-SD domain enumeration, i.e.
      _dns-sd._udp.(Zone) exists.  Forward zones MAY have this bit set,
      reverse zones MUST NOT.  This can be used to provision DNS search
      path to hosts for non-local services (such as those provided by an
      ISP, or other manually configured service providers).  Zones with
      this flag SHOULD be added to the search domains advertised to
      clients.

      Zone is the label sequence of the zone, encoded according to
      [RFC1035].  Compression MUST NOT be used.  The zone MUST end with
      an empty label.

8.2.  Domain Name TLV

   This TLV is used to indicate the base domain name for the network.
   It is the zone used as a base for all non fully-qualified delegated
   zones and node names.  In case of conflicts the announced domain of
   the node with the highest node identifier takes precedence.  By
   default ".home" is used, i.e. if no node advertises such a TLV.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: DOMAIN-NAME (40)     |         Length: > 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Domain (DNS label sequence - variable length)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Domain is the label sequence encoded according to [RFC1035].
      Compression MUST NOT be used.  The zone MUST end with an empty
      label.





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8.3.  Node Name TLV

   This TLV is used to assign the name of a node in the network to a
   certain IP address.  In case of conflicts the announcement of the
   node with the highest node identifier for a name takes precedence and
   all other nodes MUST cease to announce the conflicting TLV.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type: NODE-NAME (41)      |         Length: > 16          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                           IP Address                          |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Name (not null-terminated - variable length)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9.  Securing Third-Party Protocols

   Pre-shared keys (PSKs) are often required to secure IGPs and other
   protocols which lack support for asymmetric security.  The following
   mechanism manages PSKs using HNCP to enable bootstrapping of such
   third-party protocols and SHOULD therefore be used if such a need
   arises.  The following rules define how such a PSK is managed and
   used:

   o  If no Managed-PSK-TLV is currently being announced, an HNCP router
      MUST create one with a 32 bytes long random key and add it to its
      node data.

   o  In case multiple routers announce such a TLV at the same time, all
      but the one with the highest node identifier stop advertising it
      and adopt the remaining one.

   o  The router currently advertising the Managed-PSK-TLV must generate
      and advertise a new random one whenever an unreachable node is
      purged as described in DNCP.











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   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: Managed-PSK (42)     |          Length: 32           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                                                               |
   |                                                               |
   |                           Random PSK                          |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   PSKs for individual protocols are derived from the random PSK through
   the use of HMAC-SHA256 [RFC6234] with a pre-defined per-protocol
   HMAC-key in ASCII-format.  The following HMAC-keys are currently
   defined to derive PSKs for the respective protocols:

      "ROUTING": to be used for IGPs

10.  HNCP Versioning and Capabilities

   Multiple versions of HNCP based on compatible DNCP
   [I-D.ietf-homenet-dncp] profiles may be present in the same network
   when transitioning between HNCP versions and HNCP routers may have
   different capabilities to support clients.  The following mechanism
   describes a way to announce the currently active version and User-
   agent of a node.  Each node MUST include an HNCP-Version-TLV in its
   Node Data and MUST ignore (except for DNCP synchronization purposes)
   any TLVs with a type greater than 32 of nodes not publishing an HNCP-
   Version TLV or publishing such a TLV with a different Version number.

   Capabilities are indicated by setting M, P, H and L fields in the
   TLV.  The "capability value" is a metric indicated by interpreting
   the bits as an integer, i.e.  (M << 12 | P << 8 | H << 4 | L).

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: HNCP-VERSION (32)    |         Length: >= 5          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |   Reserved    |   M   |   P   |   H   |   L   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          User-agent                           |





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   Version:  Version indicates which version of HNCP is currently in use
      by this particular node.  It MUST be set to 0.  Nodes with
      different versions are considered incompatible.

   Reserved:  Bits reserved for future use.  MUST be set to zero when
      creating this TLV and ignored when parsing it.

   M-capability:  Priority value used for electing the on-link MDNS
      [RFC6762] proxy.  It MUST be set to some value between 1 and 7
      included (4 is the default) if the router is capable of proxying
      MDNS and 0 otherwise.  The values 8-15 are reserved for future
      use.

   P-capability:  Priority value used for electing the on-link DHCPv6-PD
      server.  It MUST be set to some value between 1 and 7 included (4
      is the default) if the router is capable of providing prefixes
      through DHCPv6-PD (Section 6.2.6) and 0 otherwise.  The values
      8-15 are reserved for future use.

   H-capability:  Priority value used for electing the on-link DHCPv6
      server offering non-temporary addresses.  It MUST be set to some
      value between 1 and 7 included (4 is the default) if the router is
      capable of providing such addresses and 0 otherwise.  The values
      8-15 are reserved for future use.

   L-capability:  Priority value used for electing the on-link DHCPv4
      server.  It MUST be set to some value between 1 and 7 included (4
      is the default) if the router is capable of running a legacy
      DHCPv4 server offering IPv4 addresses to clients and 0 otherwise.
      The values 8-15 are reserved for future use.

   User-Agent:  The user-agent is a null-terminated human-readable UTF-8
      string that describes the name and version of the current HNCP
      implementation.

11.  Requirements for HNCP Routers

   Each router implementing HNCP is subject to the following
   requirements:

   o  It MUST implement HNCP-Versioning, Border Discovery, Prefix
      Assignment and Configuration of hosts and non-HNCP routers as
      defined in this document.

   o  It MUST implement and run the method for securing third-party
      protocols whenever it uses the security mechanism of HNCP.





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   o  It SHOULD implement support for the Service Discovery and Naming
      TLVs as defined in this document.

   o  It MUST implement and run the routing protocol $FOO with support
      for source-specific routes on all of the interfaces it sends and
      receives HNCP-messages on and MUST resort to announcing source-
      specific routes for external destinations appropriately.

   o  It MUST use adequate security mechanisms for the routing protocol
      on any interface where it also uses the security mechanisms of
      HNCP.  If the security mechanism is based on a PSK it MUST use a
      PSK derived from the Managed-PSK to secure the IGP.

   o  It MUST comply with the Basic Requirements for IPv6 Customer Edge
      Routers [RFC7084] unless it would otherwise conflict with any
      requirements in this document (e.g. prefix assignment mandating a
      different prefix delegation and DHCP server election strategy).
      In general "WAN interface requirements" shall apply to external
      interfaces and "LAN interface requirements" to internal interfaces
      respectively.

   o  It SHOULD be able to provide connectivity to IPv4-devices using
      DHCPv4.

   o  It SHOULD be able to delegate prefixes to legacy IPv6 routers
      using DHCPv6-PD.

12.  Security Considerations

   HNCP enables self-configuring networks, requiring as little user
   intervention as possible.  However this zero-configuration goal
   usually conflicts with security goals and introduces a number of
   threats.

   General security issues for existing home networks are discussed in
   [RFC7368].  The protocols used to set up addresses and routes in such
   networks to this day rarely have security enabled within the
   configuration protocol itself.  However these issues are out of scope
   for the security of HNCP itself.

   HNCP is a DNCP [I-D.ietf-homenet-dncp]-based state synchronization
   mechanism carrying information with varying threat potential.  For
   this consideration the payloads defined in DNCP and this document are
   reviewed:

   o  Network topology information such as HNCP nodes and their adjacent
      links




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   o  Address assignment information such as delegated and assigned
      prefixes for individual links

   o  Naming and service discovery information such as auto-generated or
      customized names for individual links and routers

12.1.  Border Determination

   As described in Section 5, an HNCP router determines the internal or
   external state on a per-link basis.  A firewall perimeter is set up
   for the external links, and for internal links, HNCP and IGP traffic
   is allowed.

   Threats concerning automatic border discovery cannot be mitigated by
   encrypting or authenticating HNCP traffic itself since external
   routers do not participate in the protocol and often cannot be
   authenticated by other means.  These threats include propagation of
   forged uplinks in the homenet in order to e.g. redirect traffic
   destined to external locations and forged internal status by external
   routers to e.g. circumvent the perimeter firewall.

   It is therefore imperative to either secure individual links on the
   physical or link-layer or preconfigure the adjacent interfaces of
   HNCP routers to an adequate fixed-category in order to secure the
   homenet border.  Depending on the security of the external link
   eavesdropping, man-in-the-middle and similar attacks on external
   traffic can still happen between a homenet border router and the ISP,
   however these cannot be mitigated from inside the homenet.  For
   example, DHCPv4 has defined [RFC3118] to authenticate DHCPv4
   messages, but this is very rarely implemented in large or small
   networks.  Further, while PPP can provide secure authentication of
   both sides of a point to point link, it is most often deployed with
   one-way authentication of the subscriber to the ISP, not the ISP to
   the subscriber.

12.2.  Security of Unicast Traffic

   Once the homenet border has been established there are several ways
   to secure HNCP against internal threats like manipulation or
   eavesdropping by compromised devices on a link which is enabled for
   HNCP traffic.  If left unsecured, attackers may perform arbitrary
   eavesdropping, spoofing or denial of service attacks on HNCP services
   such as address assignment or service discovery.

   Detailed interface categories like "leaf" or "guest" can be used to
   integrate not fully trusted devices to various degrees into the
   homenet by not exposing them to HNCP and IGP traffic or by using




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   firewall rules to prevent them from reaching homenet-internal
   resources.

   On links where this is not practical and lower layers do not provide
   adequate protection from attackers, DNCP secure mode MUST be used to
   secure traffic.

12.3.  Other Protocols in the Home

   IGPs and other protocols are usually run alongside HNCP therefore the
   individual security aspects of the respective protocols must be
   considered.  It can however be summarized that many protocols to be
   run in the home (like IGPs) provide - to a certain extent - similar
   security mechanisms.  Most of these protocols do not support
   encryption and only support authentication based on pre-shared keys
   natively.  This influences the effectiveness of any encryption-based
   security mechanism deployed by HNCP as homenet routing information is
   thus usually not encrypted.

13.  IANA Considerations

   IANA is requested to maintain a registry for HNCP TLV-Types.

   HNCP inherits the TLV-Types and allocation policy defined in DNCP
   [I-D.ietf-homenet-dncp].  In addition the following TLV-Types are
   defined in this document:

      32: HNCP-Version

      33: External-Connection

      34: Delegated-Prefix

      35: Assigned-Prefix

      36: Node-Address

      37: DHCPv4-Data

      38: DHCPv6-Data

      39: DNS-Delegated-Zone

      40: Domain-Name

      41: Node-Name

      42: Managed-PSK



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   HNCP requires allocation of UDP port numbers HNCP-UDP-PORT and HNCP-
   DTLS-PORT, as well as an IPv6 link-local multicast address All-
   Homenet-Routers.

14.  References

14.1.  Normative references

   [I-D.ietf-homenet-dncp]
              Stenberg, M. and S. Barth, "Distributed Node Consensus
              Protocol", draft-ietf-homenet-dncp-00 (work in progress),
              January 2015.

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

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6603]  Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan,
              "Prefix Exclude Option for DHCPv6-based Prefix
              Delegation", RFC 6603, May 2012.

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

   [I-D.ietf-homenet-prefix-assignment]
              Pfister, P., Paterson, B., and J. Arkko, "Distributed
              Prefix Assignment Algorithm", draft-ietf-homenet-prefix-
              assignment-02 (work in progress), January 2015.

14.2.  Informative references

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              November 2013.

   [RFC3004]  Stump, G., Droms, R., Gu, Y., Vyaghrapuri, R., Demirtjis,
              A., Beser, B., and J. Privat, "The User Class Option for
              DHCP", RFC 3004, November 2000.

   [RFC3118]  Droms, R. and W. Arbaugh, "Authentication for DHCP
              Messages", RFC 3118, June 2001.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
              2131, March 1997.





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   [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.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets", BCP
              5, RFC 1918, February 1996.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC7368]  Chown, T., Arkko, J., Brandt, A., Troan, O., and J. Weil,
              "IPv6 Home Networking Architecture Principles", RFC 7368,
              October 2014.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              February 2013.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, February 2013.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

   [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.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.




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14.3.  URIs

   [3] http://www.openwrt.org

   [4] http://www.homewrt.org/doku.php?id=run-conf

Appendix A.  Changelog

   draft-ietf-homenet-hncp-03: Split to DNCP (generic protocol) and HNCP
   (homenet profile).

   draft-ietf-homenet-hncp-02: Removed any built-in security.  Relying
   on IPsec.  Reorganized interface categories, added requirements
   languages, made manual border configuration a MUST-support.
   Redesigned routing protocol election to consider non-router devices.

   draft-ietf-homenet-hncp-01: Added (MAY) guest, ad-hoc, hybrid
   categories for interfaces.  Removed old hnetv2 reference, and now
   pointing just to OpenWrt + github.  Fixed synchronization algorithm
   to spread also same update number, but different data hash case.
   Made purge step require bidirectional connectivity between nodes when
   traversing the graph.  Edited few other things to be hopefully
   slightly clearer without changing their meaning.

   draft-ietf-homenet-hncp-00: Added version TLV to allow for TLV
   content changes pre-RFC without changing IDs.  Added link id to
   assigned address TLV.

Appendix B.  Draft source

   This draft is available at https://github.com/fingon/ietf-drafts/ in
   source format.  Issues and pull requests are welcome.

Appendix C.  Implementation

   A GPLv2-licensed implementation of HNCP is currently under
   development at https://github.com/sbyx/hnetd/ and binaries are
   available in the OpenWrt [3] package repositories.  See [4] for more
   information.  Feedback and contributions are welcome.

Appendix D.  Acknowledgements

   Thanks to Ole Troan, Mark Baugher, Mark Townsley and Juliusz
   Chroboczek for their contributions to the draft.

   Thanks to Eric Kline for the original border discovery work.





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Authors' Addresses

   Markus Stenberg
   Helsinki  00930
   Finland

   Email: markus.stenberg@iki.fi


   Steven Barth
   Halle  06114
   Germany

   Email: cyrus@openwrt.org


   Pierre Pfister
   Cisco Systems
   Paris
   France

   Email: pierre.pfister@darou.fr





























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