Prefix Pool Option for DHCPv6 Relay Agents on Provider Edge Routers
draft-ietf-dhc-dhcpv6-prefix-pool-opt-00

DHC Working Group                                                 L. Yeh
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                T. Lemon
Expires: March 14, 2013                                     Nominum, Inc
                                                            M. Boucadair
                                                          France Telecom
                                                      September 10, 2012

  Prefix Pool Option for DHCPv6 Relay Agents on Provider Edge Routers
                draft-ietf-dhc-dhcpv6-prefix-pool-opt-00

Abstract

   The DHCPv6 Prefix Pool option provides a mechanism for DHCPv6 Prefix
   Delegation (DHCPv6-PD), allowing the DHCPv6 server to notify a DHCPv6
   relay agent implemented on a Provider Edge (PE) router about active
   prefix pools allocated by the DHCPv6 server to the PE router.  The
   information of active prefix pools can be used to enforce IPv6 route
   aggregation on the PE router by adding or removing aggregation routes
   according to the status of the prefix pools.  The advertising of the
   aggregation routes in the routing protocol enabled on the network-
   facing interface of PE routers will dramatically decreases the number
   of the routing table entries in the ISP network.

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
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   This Internet-Draft will expire on March 14, 2013.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal

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

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology and Conventions  . . . . . . . . . . . . . . . . .  4
   3.  Scenario and Network Architecture  . . . . . . . . . . . . . .  5
   4.  Prefix Pool Option . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . .  8
   6.  Server Behavior  . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Contributors List  . . . . . . . . . . . . . . . . . . . . . . 12
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 12
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13

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1.  Introduction

   The DHCPv6 protocol [RFC3315] specifies a mechanism for the
   assignment of IPv6 address and configuration information to IPv6
   nodes.  The DHCPv6 Prefix Delegation (DHCPv6-PD) [RFC3633] specifies
   a mechanism for the delegation of IPv6 prefixes from the Delegating
   Router (DR) acting as the DHCPv6 server to the Requesting Routers
   (RR) acting as the DHCPv6 Clients.  DHCPv6 servers always maintain
   authoritative information associated to their operations including,
   but not limited to, the binding data of the delegated IPv6 prefixes,
   the lease data of the delegated IPv6 prefixes, and the status of
   their prefix pools.  A prefix pool configured and maintained on the
   server can usually be a short prefix (e.g., a /40 prefix) out of
   which the longer prefixes (e.g., /56 prefixes) are delegated to
   customer networks.

   In the scenario of a centralized DHCPv6 server, the Provider Edge
   (PE) routers act as DHCPv6 relay agents when the DHCPv6 server and
   the Customer Edge (CE) router (a.k.a.  Routed-RG or Routed-CPE)
   acting as RRs and DHCPv6 clients are not on the same link.  For
   ensuring reachability, the PE routers always need to add or withdraw
   the route entries directing to each customer network in their routing
   table to reflect the status of IPv6 prefixes delegated by the DHCPv6
   server to CE routers (see Section 6.2, [BBF TR-177]).

   When a routing protocol is enabled on the network-facing interface of
   the PE router, all the routes directing to the customer networks are
   advertised in the ISP network.  This will make the number of route
   entries in the routing table on the ISP router be unacceptable large.
   Hence, it is desirable to aggregate the routes directing to the
   customer networks on the PE router.

   Because the prefixes of the customer networks can not be guaranteed
   to be active and continuous, the routing protocol enabled on the PE
   router in general can not create one aggregation route automatically
   to cover all the prefixes delegated within the prefix pool.  One way
   to make the aggregation routes (e.g., black-hole routes) pointing to
   each of the prefix pools is to configure them manually and
   permanently, but the PE router is not really aware about the status
   of the prefix pools, especially when it acts as the relay agent.

   This document proposes a new Prefix Pool option for the DHCPv6 relay
   agent implemented on PE routers, allowing the DHCPv6 server to notify
   the DHCPv6 relay agent about the prefix of pools.  After the PE
   router received information about the prefix pools, the aggregation
   route entries per the provision status of the prefix pools can be
   added or withdrawn in the routing table of the PE router.  The
   aggregation routes will then be advertised into the ISP network

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   through the routing protocol enabled on the PE's network-facing
   interface.

   DHCPv6 Bulk Leasequery [RFC5460] specifies a mechanism for bulk
   transfer of the binding data of each delegated prefix from the server
   to the requestor, typically a DHCPv6 relay agent, to support the
   replacement or reboot event of a relay agent.  In this document, the
   capability of DHCPv6 Bulk Leasequery will be extended to support the
   bulk transfer of the status of the prefix pools for route
   aggregation.

   The automatic mechanisms described in this document depend on the
   existing DHCPv6 protocols and implementations without requiring a new
   DHCPv6 message or a new interface for the configuration of the
   aggregation route.  The administrator of the ISP network can decide
   whether to inject the aggregation route or not based on the policies
   defined on the DHCPv6 server.

2.  Terminology and Conventions

   This document defines a new DHCPv6 option to communicate the prefix
   of an IPv6 prefix pool.  This document SHOULD be read in conjunction
   with the DHCPv6 specifications, [RFC3315], [RFC3633], [RFC5007] and
   [RFC5460], for understanding the complete mechanism.  Definitions for
   terms and acronyms not specified in this document are defined in
   [RFC3315], [RFC3633], [RFC3769], [RFC5007] and [RFC5460].

   The following terms can be found in this document:

   o  Requesting Router (RR): A router defined in [RFC3633] that acts as
      a DHCPv6 client, and is requesting prefix(es) to be delegated.

   o  Delegating Router (DR): A router defined in [RFC3633] that acts as
      a DHCPv6 server, and is responding to the prefix request.

   o  Prefix Pool: An IPv6 address space allocated with a common prefix
      out of which the longer prefixes are delegated via prefix
      delegation.

   o  aggregation Route: A route entry created on an edge router, is
      based on the knowledge of a delegated prefix pool.

   o  Requestor: A node defined in [RFC5007] that acts as the leasequery
      client.

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this

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   document, are to be interpreted as described in BCP 14, [RFC2119].

3.  Scenario and Network Architecture

   Figure 1 and Figure 2 illustrate two typical cases of the targeted
   network architectures.

             +------+------+  DHCPv6 Server
             |    DHCPv6   |  (e.g. Binding entry
             |    Server   |        pe#1 - 2001:db8:1230::/44
             |             |        extract PE_ID=pe#1
             +------+------+        from the Interface_ID=pe#1_cfi#2)
                    |
           _________|_________
          /                   \
         |   ISP Core Network  |
          \___________________/
                    |
                    |  Network-facing interface
             +------+------+
             |   Provider  |  DHCPv6 Relay Agent, DHCPv6 Requestor
             |     Edge    |  (e.g. prefix pool=2001:db8:1230::/44)
             |    Router   |
             +------+------+
                    |  Customer-facing interface
                    |         (e.g. Interface_ID=pe#1_cfi#2)
                    |
             +------+------+
             |   Customer  |  DHCPv6 Client
             |     Edge    |  DHCPv6-PD Requesting Router
             |    Router   |  (e.g. customer network
             +------+------+        =2001:db8:1234:5600:/56)
                    |
           _________|_________
          /                   \
         |  Customer Network   |
          \___________________/

     Figure 1: Use case of ISP-Customer network where CPE is directly
                              connected to PE

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             +------+------+
             |    DHCPv6   |  DHCPv6 Server
             |    Server   |  (e.g. Binding entry
             |             |        pe#3_cfi#4 - 2001:db8:3400::/40)
             +------+------+
                    |
           _________|_________
          /                   \
         |  ISP Core Network   |
          \___________________/
                    |
                    |  Network-facing interface
             +------+------+
             |   Provider  |  DHCPv6 Relay Agent, DHCPv6 Requestor
             |     Edge    |  (e.g. prefix pool=2001:db8:3400::/40)
             |    Router   |
             +------+------+
                    |  Customer-facing interface
                    |         (e.g. Interface_ID=pe#3_cfi#4)
           _________|_________
          /                   \
         |   Access Network    |
          \___________________/
                    |
                    |
             +------+------+
             |   Customer  |  DHCPv6 Client
             |     Edge    |  DHCPv6-PD Requesting Router
             |    Router   |  (e.g. customer network
             +------+------+        =2001:db8:1234:5600:/56)
                    |
           _________|_________
          /                   \
         |  Customer Network   |
          \___________________/

   Figure 2: Use case of ISP-Customer network where CPE is connected to
                         PE through access network

4.  Prefix Pool Option

   The format of the Prefix Pool option is shown in Figure 3.

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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      OPTION_PREFIX_POOL       |         option-length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    status     | pfx-pool-len  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                 ipv6-prefix (variable length)                 |
   |                                                               |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:    OPTION_PREFIX_POOL (TBD)
   option-length:  2 + length of ipv6-prefix (in Octets)
   pfx-pool-len:   Length for the prefix pool in bits
   status:         Status of the prefix pool, indicating the
                   availability of the prefix pool maintained
                   on the server.
   ipv6-prefix:    IPv6 prefix of the prefix pool, which is up to 16
                   octets in length. Bits outsides of the
                   pfx-pool-len, if included, MUST be zero.

   The codes of the status are defined in the following table.

   Name      Code
   Active    0
   Released  1
   Reserved  2~255

   The 'Active' status of the prefix pool indicated in this option can
   be used to add the prefix pool and its associated aggregation route
   on the relay agent; while the 'Released' status of prefix pool
   indicated in this option can be used to withdraw the prefix pool and
   its associated aggregation route on the relay agent.

   If the administrative policy on the DHCPv6 server permits to support
   route aggregation on the relay agent, the status of prefix pool can
   be determined by the delegated prefixes within the associated prefix
   pool.  If there is one delegated prefix within the pool that has a
   valid lease, the status of the prefix pool will be 'Active'.
   Otherwise, the status of the prefix pool is 'Released'.  If the
   administrative policy on the server does not permit to support route
   aggregation on the DHCPv6 relay agent, the status of the prefix pool
   will always be 'Released'.

   Discussion:

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      The alternative option might include the lease information in the
      prefix pool, then populate it to relay agent, make the state
      machine on the relay agent keep synchronizing the lease and status
      of the associated prefix pool with the server.  But the solution
      proposed in this draft is to let relay agent confirm the received
      status of the prefix pool by itself as per the leases of delegated
      customer prefixes within it, and build its own lease for the
      prefix pool.

   Prefix Pool Option MAY be included by the DHCPv6 server in RELAY-REPL
   (13), LEASEQUERY-REPLY (15) and LEASEQUERY-DATA (17) message, or MAY
   be included by the DHCPv6 relay agent in the RELAY-FORW (12).

5.  Relay Agent Behavior

   The relay agent who needs the information of prefix pools, MUST
   include the associated requested-option-code in Option Request option
   (OPTION_ORO, 6) to request the Prefix Pool option
   (OPTION_PREFIX_POOL, [TBD]) from the DHCPv6 server, who maintains the
   status of the prefix pools associated to the relay agent itself
   (Figure 1) or its particular customer-facing interface (Figure 2),
   when receiving the DHCPv6-PD message from clients.  The DHCPv6 relay
   agent MAY include this Option Request option for the Prefix Pool
   option in the RELAY-FORW (12) message of SOLICIT (1), REQUEST (3),
   RENEW(5), REBIND (6) and RELEASE (8).  The relay agent MAY also
   include the Prefix Pool option with the values of pfx-pool-len and
   IPv6-prefix to indicate its preference, which prefix pool the relay
   agent would like the server to return.

   The relay agent SHOULD include the Interface ID option
   (OPTION_INTERFACE_ID, 18) so that the DHCPv6 server can identify the
   relay agent itself or its particular customer-facing interface to
   which the prefix pool is associated, if the server would not like to
   use the link-address field specified in the encapsulation of the
   DHCPv6 relay-forward message to identify the interface of the link on
   which the clients are located.

   The relay agent MAY set up a table for the leases and/or status of
   the prefix pools on it as per the delegated customer prefixes within
   it.  The lease of the prefix pools MUST dynamically set to be the
   maximum lease of the delegated customer prefixes.  If there is no
   route entry directing to the customer network within the aggregation
   route associated with the prefix pool, the relay agent shall
   automatically withdraw the aggregation route.

   After receiving the Prefix Pool option for the relay agent itself or
   its particular customer-facing interface in the relay-reply message

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   (13) of REPLY (7) from the DHCPv6 server, the relay agent acting as
   the PE router shall confirm the status of the prefix pool as per the
   leases of delegated customer prefixes within it, then add the
   aggregation route entry per the status of the prefix pool.  If the
   status of the prefix pool received and confirmed is 'Active', the
   relay agent shall add an aggregation route entry in its routing
   table, if the same entry has not been added in before.  If the status
   of the prefix pool received is 'Released', the relay agent shall
   withdraw the associated aggregation route entry in its routing table,
   if the same entry has not been withdrawn before.

   The relay agent advertises its routing table including the entries of
   the aggregation routes based on the information of prefix pools when
   the routing protocol is enabled on its network-facing interface.

   The Relay Agent (i.e., Requestor) can use the DHCPv6 Bulk Leasequery
   [RFC5460] to query the binding data of prefix pools in the 'Active'
   status from the server.  After established a TCP connection with the
   DHCPv6 server, the relay agent MUST include Query option
   (OPTION_LQ_QUERY, 44) and set the proper query-type
   (QUERY_BY_RELAY_ID, QUERY_BY_LINK_ADDRESS, QUERY_BY_REMOTE_ID), link-
   address and query-options in the LEASEQUERY (14) message.  The query
   options MUST include Option Request option (OPTION_ORO, 6) to request
   the Prefix Pool option (OPTION_PREFIX_POOL, [TBD]) from the server.

6.  Server Behavior

   Per DHCPv6-PD [RFC3633], if the prefix of the customer network
   requested in relay-forward (12) message of SOLICIT, REQUEST, RENEW,
   REBIND from the DHCPv6 client (i.e., the RR) has a valid lease, the
   DHCPv6 server (i.e., the DR) will delegate the prefix with the
   relevant parameters in the relay-reply (13) message of REPLY.  In
   order to give a meaningful reply, the server has to be able to
   maintain the binding data of the delegated IPv6 prefixes with the
   identification of the client.  The Interface ID option
   (OPTION_INTERFACE_ID, 18) nested in the relay-forward message is
   usually used to identify the access line of the client.

   After receiving the Option Request option (OPTION_ORO, 6) requesting
   the Prefix Pool option (OPTION_PREFIX_POOL, [TBD]) in the relay-
   forward messages of the DHCPv6-PD, the server MUST include the Prefix
   Pool option with the status indicated for the associated relay agent
   itself (Figure 1) or its customer-facing interface (Figure 2) in the
   relay-reply messages if the relay-forward messages received are
   valid.

   The server MAY use the link-address specified in relay-forward

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   message to identify the relay agent itself or its particular
   customer-facing interface where the prefix pool is associated, but
   the server has to maintain the binding data of prefix pools in
   association with these link-addresses.  To be more readable, the
   server can alternatively use the Interface ID option
   (OPTION_INTERFACE_ID, 18) included in the relay-forward message by
   the relay agent to identify the relay agent itself (Figure 1) or its
   particular customer-facing interface (Figure 2) where the prefix pool
   is associated.  In order to give a meaningful reply, the server has
   to maintain the binding data of prefix pools in association with the
   information derived from the Interface ID option.

   Per DHCPv6 [RFC3315], the server shall copy the same Interface ID
   option received via the relay-forward message into the relay-reply
   message.

   If the administrative policy on the DHCPv6 server permits to support
   route aggregation on the relay agent for some particular prefix, the
   status of prefix pool can be determined by the delegated prefixes
   within the associated prefix pool.  If there is at least one
   delegated prefix within the pool that has a valid lease, the server
   shall set the status of the associated prefix pool to be 'Active'.
   After the last prefix releasing in the associated prefix pool, the
   server shall set the status of the associated prefix pool to be
   'Released'.  If the administrative policy on the server does not
   permit to support route aggregation on the DHCPv6 relay agent, the
   server shall set the status of the prefix pools always to be
   'Released'.

   When the administrator of the server changes the setting to support
   route aggregation on the relay agent for the particular prefix pool,
   the status of the prefix pool MAY change from 'Released' to be
   'Active' if at least one delegated prefix within the prefix pool has
   the valid lease.  When the administrator of the server changes the
   setting not to support route aggregation on the relay agent for the
   particular prefix pool, the status of the prefix pool MAY change from
   'Active' to be 'Released' if at least one delegated prefix within the
   prefix pool has the valid lease.  Then the server MAY send a relay-
   reply message of RECONFIGURE (10) to initiate immediately a Renew (5)
   / Reply (7) PD message exchange with Prefix Pool option between one
   active client and the server.

   Multiple prefix pools MAY be associated with the same PE router
   implementing a DHCPv6 relay agent (Figure 1) or its customer-facing
   interface (Figure 2) in the binding table on the server.  Note that
   these prefix pools don't overlay, and the delegated customer prefix
   is only from one prefix pool.

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   After receiving the LEASEQUERY (14) message from the relay agent with
   the Query option (OPTION_LQ_QUERY, 44) including the Option Request
   option (OPTION_ORO, 6) to request the Prefix Pool option
   (OPTION_PREFIX_POOL, [TBD]), the server MUST include the Client Data
   options (OPTION_CLIENT_DATA, 45) in the LEASEQUERY-REPLY (15) and
   LEASEQUERY-DATA (17) message to convey the binding data of the
   associated prefix pools with the 'Active' status through the
   established TCP connection per [RFC5460].  Each Client Data option
   shall contain a Prefix Pool option, and MAY contain the Interface ID
   option (OPTION_INTERFACE_ID, 18).  In order to be able to provide
   meaningful replies to different query types, the server has to be
   able to maintain the relevant association of prefix pools with the
   RELAY_ID, link addresses or Remote_ID of the relay agent in its
   binding database.

7.  Security Considerations

   Security issues related DHCPv6 are described in Section 23 of
   [RFC3315] and Section 15 of [RFC3633].

8.  IANA Considerations

   IANA is requested to assign an option code to Option_Prefix_Pool from
   the "DHCPv6 and DHCPv6 options" registry
   (http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-
   parameters.xml).

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9.  Contributors List

   Juergen Schoenwaelder
   Jacobs University Bremen
   Bremen
   Germany

   Email: j.schoenwaelder@jacobs-university.de

   Jie Hu
   China Telecom
   Beijing,
   P. R. China

   Email: huj@ctbri.com.cn

   Tina Tsou
   Huawei Technologies
   Santa Clara, CA
   USA

   Email: tina.tsou.zouting@huawei.com

10.  Acknowledgements

   Thanks to Ralph Droms for the inspiration from his expired draft
   (RAAN option), to the DHC working group members, Bernie Volz, Ole
   Troan and Roberta Maglione for the discussion in the mailing list, to
   Christian Jacquenet for pointing out the draft shall cover one more
   use case of ISP-Customer network where CPE is directly connected to
   PE, to Sven Ooghe for some revisions in the email review, to
   Shrinivas Ashok Joshi for pointing out the draft shall cover the
   robust mechanism against the case of reboot, to Adrian Farrel for the
   orientation guide on this draft in IETF80 at Prague.

11.  References

11.1.  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.

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

   [RFC5007]  Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
              "DHCPv6 Leasequery", RFC 5007, September 2007.

   [RFC5460]  Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460,
              February 2009.

11.2.  Informative References

   [BBF TR-177]
              Broadband Forum, "IPv6 in the context of TR-101, Issue 1",
              November 2010.

   [RFC3769]  Miyakawa, S. and R. Droms, "Requirements for IPv6 Prefix
              Delegation", RFC 3769, June 2004.

Authors' Addresses

   Leaf Y. Yeh
   Huawei Technologies
   Shenzhen,
   P. R. China

   Email: leaf.y.yeh@huawei.com

   Ted Lemon
   Nominum, Inc
   USA

   Email: Ted.Lemon@nominum.com

   Mohamed Boucadair
   France Telecom
   Rennes,
   France

   Email: mohamed.boucadair@orange.com

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