DHC Working Group                                                 Q. Sun
Internet-Draft                                       Tsinghua University
Intended status: Standards Track                                  Y. Lee
Expires: April 15, 2014                                          Comcast
                                                                  Q. Sun
                                                           China Telecom
                                                                G. Bajko
                                                            M. Boucadair
                                                          France Telecom
                                                        October 12, 2013

     Dynamic Host Configuration Protocol (DHCP) Option for Port Set


   Because of the exhaustion of the IPv4 address space, several
   techniques have been proposed to share the same IPv4 address among
   several uses.  As an alternative to introducing a level of NAT in the
   provider's core network, this document provides a mechanism to assign
   non-overlapping layer 4 port sets to users assigned with the same
   IPv4 address: Port Set DHCPv4 Option.

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 April 15, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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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.  DHCPv4 Port Set Option . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Port Set Option Format . . . . . . . . . . . . . . . . . .  3
     3.2.  Port Set Option Example  . . . . . . . . . . . . . . . . .  5
   4.  Server Behavior  . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Client Behavior  . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Security Consideration . . . . . . . . . . . . . . . . . . . .  7
     6.1.  Denial-of-Service  . . . . . . . . . . . . . . . . . . . .  7
     6.2.  Port Randomization . . . . . . . . . . . . . . . . . . . .  7
   7.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . .  7
   8.  Contributors List  . . . . . . . . . . . . . . . . . . . . . .  7
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

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1.  Introduction

   Currently some large ISPs still have a large enough IPv4 address pool
   to be able to allocate public IPv4 addresses for their subscribers.
   However, due to the exhaustion of the global IPv4 address space,
   these ISPs expect the situation is unsustainable and they will not be
   able anymore to assign to every requesting host a public IPv4

   Two solutions have been proposed so far: (1) Deploy Network Address
   Translation (NAT) or (2) Allocate the same public IPv4 address with
   non-overlapped layer 4 port sets directly to multiple connected
   devices (which can be CPEs or end hosts).  This document focuses on
   the second solution.

   This document describes a new DHCPv4 option which allows the DHCPv4
   server to assign a set of ports to a user device during the IPv4
   address provisioning process.  By assigning the same IPv4 address
   with non-overlapped port sets to multiple clients, the clients is
   enabled to share the IPv4 address and continue to deliver IPv4
   services to subscribers.

   When using this DHCPv4 option, the underlaying forwarding carrier
   should be other than IPv4 to avoid affecting the current IPv4-only
   architecture, for example IPv6 [I-D.ietf-dhc-dhcpv4-over-ipv6],
   [I-D.ietf-dhc-dhcpv4-over-dhcpv6], etc.  The server has to manage to
   forward DHCP responses to the right client.

   The Port Set Option described in this document can be used in various
   deployment scenarios, some of which are described in [RFC6346]

2.  Requirements Language

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

3.  DHCPv4 Port Set Option

3.1.  Port Set Option Format

   The format of Port Set Option is shown in Figure 1.

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            0                             1
            0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
           |   OPTION_PORT_SET     |     option-length     |
           |                Port Set Index                 |
           |                Port Set Mask                  |

   Figure 1 Port Set Option Format

   o  option-code: OPTION_PORT_SET (TBD)

   o  option-length: An 8-bit field indicating the length of the option
      excluding the 'Option Code' and the 'Option Length' fields.  In
      this option, the option-length is 4 octets.

   o  Port Set Index: Port Set Index identifies a set of ports assigned
      to a device.  The first k bits on the left of the 2-octet field is
      the Port Set Index value, with the rest of the field right padding

   o  Port Set Mask: Port Set Mask indicates the position of the bits
      used to build the mask.  The first k bits on the left is padding
      ones while the remained (16-k) bits of the 2-octet field on the
      right is padding zeros.

   In the context of Port Set Option, the port number should consist of
   port set prefix and port number suffix.  The port set prefix can be
   got from Port Set Index and Port Set Mask, while port number suffix
   can change continuously.  The format of port number is shown in
   Figure 2.

           0                                                    15
           |    port set prefix    |      port number suffix     |
           |<-------k bits-------->|<--------(16-k) bits-------->|

   Figure 2 Bit Representation of a port number

   In order to exclude the system ports ([I-D.ietf-tsvwg-iana-ports]) or
   ports saved by SPs, the former port-sets that contains well-known
   ports SHOULD NOT be assigned.

   For example: If k is 10 (the left 10 bits of Port Set Mask is '1'),
   the first 16 port sets is located in well-known port space, which

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   should not be allocated.  Or,

   For example: If k is 4 (the left 4 bits of Port Set Mask is '1'), the
   first port set (0 - 4095) contains the well-know port space.  It
   should be perceived as well.

3.2.  Port Set Option Example

   The Port Set Option is used to specify one contiguous port set
   pertaining to the given IP address.

   Concretely, this option is used to notify a remote DHCP client about
   the port set prefix to be applied when selecting a port value as a
   source port.  The Port Set Option is used to infer a set of allowed
   contiguous port values.  Two port numbers are said to belong to the
   same Port Set if and only if, they have the same port set prefix.

   The following Port Set Index and Port Set Mask are conveyed using
   DHCP to assign a contiguous port set with excluding well-know ports
   (with Port Set Index not zero):

   Port Set Index: 0001 0100 0000 0000 (5120)

   Port Set Mask: 1111 1100 0000 0000 (64512)

   The device will get a contiguous port set: 5120 - 6143

4.  Server Behavior

   The server will not reply with the option until the client has
   explicitly listed the option code in the Parameter Request List
   (Option 55).

   Server MUST reply with Port Set Option if the client requested
   OPTION_PORT_SET in its Parameter Request List.  In order to achieve
   the dynamic management of IPv4 address and port set in the address
   sharing environment, the server MUST run an address & port-set pool
   that plays the same role as address pool in regular DHCP server.  The
   address and port-set pool MUST follow the Port-Mask-format port-set.
   The server MUST use a combination of address & port-set as a key to
   maintain the state of a lease, and look for an available lease for
   assignment.  The leasing database MUST also include the information
   of the address and port-set.

   When a server receives a DHCPDISCOVER message with OPTION_PORT_SET in
   the Parameter Request List from a client, the server chooses an IPv4
   address and a port-set for the requesting client.  The logic of

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   choosing is similar to that in Section 4.3.1 of [RFC2131], while the
   difference is the server looks for the client's binding or an
   available lease in the server's pool of addresses & port-sets.  After
   selecting an available combination of an address and a port-set, the
   server puts the address into the 'yiaddr' field and the port-set (in
   the Port-Mast-format) into the Port Set Option.

   If the server receives a DHCPDISCOVER message containing a Port Set
   Option, this means the client is requesting a specific port set.  The
   Port Set Mask field in the option indicates the size of port set that
   the client requests.  The server MAY reply with a Port Set Option
   whose Port Set Mask is as requested, if the server has such one port
   set.  Or the server can ignore the request and just assign a port set
   from the pool.

   When a server receives a DHCPREQUEST message with Port Set Option,
   the server MUST determine the client's state according to related
   parameters (Section 4.3.2 of [RFC2131]) and the value of Port Set

   Upon reception of a DHCPRELEASE message with Port Set Option, the
   server looks for the lease using the address and the value in the
   Port Set Option, and marks it as unallocated.

   The port-set assignment MUST be coupled with the address assignment
   process.  Therefore server MUST assign the address and port set in
   the same DHCP messages.  And the lease information for the address is
   applicable to the port-set as well.

5.  Client Behavior

   The DHCP client applying for a port-set MUST include the
   OPTION_PORT_SET code in the Parameter Request List (Option 55).  The
   client retrieves a Port Set Option and use the Port Set Index and
   Port Set Mask to perform the port mask algorithm to get the
   contiguous port set.

   When the client renews or releases the DHCP lease, it MUST put its
   Port Set Index and Port Set Mask into the Port Set Option, and send
   to the server within corresponding DHCPv4 messages.

   The client MAY include a Port Set Option in the DHCPDISCOVER message,
   in which the Port Set Mask field indicates the requested size of a
   port set from the client.

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6.  Security Consideration

6.1.  Denial-of-Service

   The solution is generally vulnerable to DoS when used in shared
   medium or when access network authentication is not a prerequisite to
   IP address assignment.  The solution SHOULD only be used on point-to-
   point links, tunnels, and/or in environments where authentication at
   link layer is performed before IP address assignment, and not shared

6.2.  Port Randomization

   Preserving port randomization [RFC6056] may be more or less difficult
   depending on the address sharing ratio (i.e., the size of the port
   space assigned to a CPE).  The host can only randomize the ports
   inside a fixed port range [RFC6269].

   More discussion to improve the robustness of TCP against Blind In-
   Window Attacks can be found at [RFC5961].  Other means than the
   (IPv4) source port randomization to provide protection against
   attacks should be used (e.g., use [I-D.vixie-dnsext-dns0x20] to
   protect against DNS attacks, [RFC5961] to improve the robustness of
   TCP against Blind In-Window Attacks, use IPv6).

   A proposal to preserve the entropy when selecting port is discussed
   in [I-D.bajko-pripaddrassign]

7.  IANA Consideration

   IANA is kindly requested to allocate DHCP option code to the
   OPTION_PORT_SET.  The code should be added to the DHCP option code

8.  Contributors List

   Many thanks for valuable comments and great efforts from the
   following contributors:

      Peng Wu
      Tsinghua University


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      Teemu Savolainen


      Ted Lemon
      Nominum, Inc.


      Tina Tsou
      Huawei Technologies


      Pierre Levis
      France Telecom

      Email: pierre.levis@orange.com

      Cong Liu
      Tsinghua University

      Email: gnocuil@gmail.com

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.

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

   [RFC5961]  Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
              Robustness to Blind In-Window Attacks", RFC 5961,

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              August 2010.

   [RFC6056]  Larsen, M. and F. Gont, "Recommendations for Transport-
              Protocol Port Randomization", BCP 156, RFC 6056,
              January 2011.

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269,
              June 2011.

   [RFC6346]  Bush, R., "The Address plus Port (A+P) Approach to the
              IPv4 Address Shortage", RFC 6346, August 2011.

9.2.  Informative References

              Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
              "Port Restricted IP Address Assignment",
              draft-bajko-pripaddrassign-04 (work in progress),
              April 2012.

              Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
              Farrer, "DHCPv4 over DHCPv6 Transport",
              draft-ietf-dhc-dhcpv4-over-dhcpv6-01 (work in progress),
              July 2013.

              Cui, Y., Wu, P., Wu, J., and T. Lemon, "DHCPv4 over IPv6
              Transport", draft-ietf-dhc-dhcpv4-over-ipv6-07 (work in
              progress), September 2013.

              Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry",
              draft-ietf-tsvwg-iana-ports-10 (work in progress),
              February 2011.

              Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to
              Improve Transaction Identity",
              draft-vixie-dnsext-dns0x20-00 (work in progress),
              March 2008.

   [RFC6842]  Swamy, N., Halwasia, G., and P. Jhingran, "Client
              Identifier Option in DHCP Server Replies", RFC 6842,

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              January 2013.

Authors' Addresses

   Qi Sun
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084

   Phone: +86-10-6278-5822
   Email: sunqi@csnet1.cs.tsinghua.edu.cn

   Yiu L. Lee
   One Comcast Center
   Philadelphia  PA  19103

   Email: yiu_lee@cable.comcast.com

   Qiong Sun
   China Telecom
   Room 708, No.118, Xizhimennei Street
   Beijing  100035

   Phone: +86-10-58552936
   Email: sunqiong@ctbri.com.cn

   Gabor Bajko

   Email: gabor.Bajko@nokia.com

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   Mohamed Boucadair
   France Telecom
   2330 Central Expressway
   Rennes  35000

   Email: mohamed.boucadair@orange.com

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