PCP Server Discovery with IPv4 traffic offload for Proxy Mobile IPv6
draft-rpcw-pcp-pmipv6-serv-discovery-03

Abstract

This document proposes a solution to PCP Server Discovery problems in Proxy Mobile IPv6 (PMIPv6) networks when both home network traffic and traffic off-loaded to local access network require traversing a gateway implementing NAT and/or Firewall. This draft proposes enhancements to DHCPv4 Relay Agent by introducing a new sub-option under DHCPv4 Relay Option and to PMIPv6 signaling through additional options to Proxy Binding Update/Acknowledgement messages.

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 February 15, 2014.

Copyright Notice

Copyright (c) 2013 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 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Solution overview
• 4. Mobility Options
• 5. DHCPv4 Relay Agent co-located with MAG
• 5.1. Format
• 5.2. Relay Agent behavior
• 5.3. DHCPv4 Server behavior
• 6. DHCPv4 Server co-located with MAG
• 7. Security Considerations
• 8. IANA Considerations
• 9. Acknowledgements
• 10. Change History
• 10.1. Changes from draft-rpcw-pcp-pmipv6-serv-discovery-01 to -02
• 10.2. Changes from draft-rpcw-pcp-pmipv6-serv-discovery-02 to -03
• 11. References
• 11.1. Normative References
• 11.2. Informative References
• Authors' Addresses

1. Introduction

Given the exponential growth in the mobile data traffic, Mobile Operators are looking for ways to offload some of the IP traffic flows at the nearest access edge that has an Internet peering point. This approach results in efficient usage of the mobile packet core and helps lower the transport cost. [RFC6909] defines a mechanism for Mobile Access Gateway (MAG) and the Local Mobility Anchor (LMA) to negotiate Ipv4 traffic offload policy for mobility sessions in Proxy Mobile IP Networks. There are scenarios in PMIPv6 Mobile Networks where the traffic going through the Mobile Packet Core as well as the traffic that is off-loaded to the Local Access Networks end up going through a NAT or Firewall gateway. If the mobile node applications desire to find or control the external addresses assigned to the internal address used by the Mobile Node (MN), it could be achieved by having a Port Control Protocol (PCP) Client on the mobile node.

[I-D.ietf-pcp-dhcp] specifies DHCP (IPv4 and IPv6) options to communicate Port Control Protocol (PCP) Server addresses to hosts. However, PCP Client on the mobile node will not know whether a flow will traverse the Mobile Packet Core or will get offloaded at the local access network and hence will not know which PCP server to send its queries to. Even if the mobile node tries to find its PCP server using DHCP, it may only find out about the PCP server in the Home Network since the source of information is the DHCP server in the Home Network. The mobile node may never learn the presence of the PCP server in the Local Access Network. This requires mobile access gateway to act as a PCP Proxy for the PCP server in the mobile node's home network and as a PCP server/PCP Proxy for the NAT that the offloaded traffic at the Local Access Network have to traverse through. However, this alone does not solve this problem since the mobile node needs to be informed of the PCP proxy on the MAG. This draft proposes an extension to DHCPv4 Relay Information Option and PMIPv6 Options to achieve these objectives.

2. Terminology

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 [RFC2119].

All the mobility related terms used in this document are to be interpreted as defined in the Proxy Mobile IPv6 specifications [RFC5213], [RFC5844]. This note also uses terminology defined in [RFC6887].

Additionally, this document uses the following abbreviations:

• IP Flow - IP Flow represents a set of IP packets that match a traffic selector. The selector is typically based on the source IP address, destination IP address, source port, destination port and other fields in upper layer headers.
• IP Traffic Offload - The approach of selecting specific IP flows and routing them to the local network, as supposed to tunneling them to the home network.
• NAT (Network Address Translation) - Network Address Translation [RFC2663] is a method by which IP addresses are mapped from one address realm to another, providing transparent routing to end hosts.
• Firewall (FW) - A packet filtering device that matches packets against a set of policy rules and applies the actions.
• peer-to-peer (P2P) - Applications and protocols, such as teleconferencing, multiplayer online gaming, BitTorrent etc
• Internal Address - The address of Mobile Node assigned by the home agent.
• Remote Peer IP Address - The address of a Remote Peer, as seen by the Mobile Node. A Remote Address is generally a publicly routable address.
• External Address - The address of the Mobile Node as seen by other Remote Peers on the Internet with which the Mobile Node is communicating, after translation by any NAT gateways on the path.

3. Solution overview

The following illustrates a scenario where the Mobile Node is a PCP client, Mobile Access Gateway in the access network is a PCP server with PCP proxy functionality [I-D.ietf-pcp-proxy], the home network has a PCP server.

Mobile access gateway has the ability to offload some of the IPv4 traffic flows based on the traffic selectors it receives from the local mobility anchor. Using IPv4 Traffic Offload Selector option [RFC6909] mobile access gateway will negotiate IP Flows that can be offloaded to the local access network or internet. For example, consider a mobile node acting as both client and server for FTP, VoIP and P2P. In this case FTP flows for that mobility session may be offloaded at the mobile access gateway and P2P, Voice over IP (VoIP) flows tunneled back to the local mobility anchor. Mobile node uses PCP to create mappings between external IP address/port and internal IP address/port. These mappings will be used for successful inbound communication destined to the mobile node behind NAT and/or firewall.

The mobile node learns the PCP server IP addresses from DHCPv4 server using DHCPv4 option OPTION_PCP_SERVER [I-D.ietf-pcp-dhcp]. If IP Flows are offloaded at the mobile access gateway then the mobile node needs to learn the IP address of the mobile access gateway acting as PCP proxy. Mobile access gateway will compare the Remote Peer IP Address and Port fields set in PCP PEER request from the mobile node with the Traffic Selector fields and IP Traffic Offload Mode Flag in IP Traffic Offload Selector Option to determine if the dynamic outbound mapping is to be created in the local access network or home network. In case of PCP MAP request mobile access gateway will compare the Remote Peer IP Address and Port fields in FILTER Option with the Traffic Selector fields and IP Traffic Offload Mode Flag in IP Traffic Offload Selector Option to determine if dynamic outbound mapping is to be created in the local access network or home network. For PCP MAP request without FILTER option since the Remote Peer IP Address is not available the mobile access gateway will function as a PCP proxy and forward the PCP MAP request to the PCP server in the home network. Mobile Nodes which require communication with well known peers (For e.g. applications like SIP proxy, FTP server) will use PCP MAP with FILTER option. When MNs act as servers (such as P2P server, Web Server) i.e., when the remote peer IP address is not known, PCP client will use PCP MAP request in which case the MAG cannot make a decision as per the traffic selector fields and hence will relay the request to a PCP server based on local configuration.

If the dynamic outbound mapping is for Internet Offload, then the mobile access gateway will function as a PCP server for the mobile node if the NAT is co-located on the MAG. If the NAT is not co-located, then MAG will act as a proxy and forward the PCP requests to the respective PCP server in the Local Access Network.

NAT may not always be required for traffic offloaded for local access. If there is NAT required for traffic offloaded for Local Access, then, the dynamic outbound mapping is for the Local Access Network. In this case, the Mobile Access Gateway will function as a PCP server if NAT device for the Local Access Network is co-located on the MAG, otherwise, it will act as a PCP proxy forwarding the PCP requests to the respective PCP server on the Local Access Network.

If dynamic outbound mapping is for the home network then mobile access gateway will function as PCP proxy and forward the accepted PCP requests to the PCP server in the home network.

                                   _----_
                                 _(      )_
              :-----------------( Internet )---------------:
              |                  (_      _)                |
              |                    '----'                  |
              |                                            |
              :                                            |
   (IPv4 Traffic Offload Point)                            |
              :                                            |
              |                                            |
   ........................................................|....
              |                              |             |
   +--------+ |                   +---------------------+  |
   |  Local | |                   | Services requiring  |  |
   |Services| |                   | mobility, or service|  |
   +--------+ |                   | treatment           |  |
        |     |                   +---------------------+  |
        |   +---+                            |             |
        |   |NAT|                            |             |
        |   +---+                            |             |
        +-----|            _----_            |             |
           +-----+       _(      )_       +-----+          |
   [MN]----| MAG |======(    IP    )======| LMA |----------
           +-----+       (_      _)       +-----+  Internet
                           '----'
                              .
                              .
       [Access Network]       .        [Home Network]
   ..........................................................   

       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     |   Length      |    Reserved (R)           |S|P|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       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     |   Length      |         Reserved (R)          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  PCP Server IP address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  PCP Server IP address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                     ...

    MN  MAG(DHCP-R) LMA DHCP-S
    |------>|        |    |     1. Mobile Node Attach
    |       |------->|    |     2. Proxy Binding Update
    |       |<-------|    |     3. Proxy Binding Acknowledgement 
    |       |        |    |        (IPTS Option)
    |       |========|    |     4. Tunnel/Route Setup
    |       +        |    |     5. Installing the traffic offload rules
    |<----->|<----------->|     6. DHCP OFFER/REQUEST/ACK exchange
    |       |        |    |        OPTION_PCP_SERVER inserted by DHCP-R
    |------>|        |    |     7. IPv4 packet from mobile node
    |       +        |    |     8. Forwarding rule - Tunnel home/offload
    |       |        |    |

          Code  Length   PCP IP address
         +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
         | TBA |  n  |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 |  a3 |  a4 |  ...
         +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

    MN  MAG(DHCP-S) LMA
    |------>|        |   1. Mobile Node Attach
    |       |------->|   2. Proxy Binding Update
    |       |<-------|   3. Proxy Binding Acknowledgement 
    |       |        |      (IPTS Option)
    |       |========|   4. Tunnel/Route Setup
    |       +        |   5. Installing the traffic offload rules
    |<----->|        |   6. DHCP OFFER/REQUEST/ACK exchange
    |       |        |      OPTION_PCP_SERVER inserted by DHCP-S
    |------>|        |   7. IPv4 packet from mobile node
    |       +        |   8. Forwarding rule - Tunnel home/offload
    |       |        |