PCP Server Selection
draft-ietf-pcp-server-selection-02

Abstract

Multiple IP addresses may be configured on a PCP client in some deployment contexts such as multi-homing. This document specifies the behavior to be followed by the PCP client to contact its PCP server(s) when one or several PCP server IP addresses are configured.

This document updates RFC6887.

Requirements Language

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

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on July 10, 2014.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents 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. IP Address Selection
• 4. Multiple Interfaces
• 5. Example: Multiple PCP servers on a Single Interface
• 6. Security Considerations
• 7. IANA Considerations
• 8. Acknowledgements
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Appendix A. Multi-homing
• A.1. IPv6 Multi-homing
• A.2. IPv4 Multi-homing
• Authors' Addresses

1. Introduction

Multiple IP addresses may be configured on a PCP client in some deployment contexts such as multi-homing (see Appendix A). A PCP server may also have multiple IP addresses associated with it. This document specifies the behavior to be followed by the PCP client [RFC6887] to contact its PCP server(s) [RFC6887] when it receives one or several PCP server IP addresses (e.g., using DHCP [I-D.ietf-pcp-dhcp]).

This document is not specific to DHCP; any other mechanism can be used to configure PCP server IP addresses.

It is out of scope of this document to enumerate all deployment scenarios that require multiple IP addresses to be configured.

2. Terminology

This document makes use of the following terms:

• PCP server denotes a functional element that receives and processes PCP requests from a PCP client. A PCP server can be co-located with or be separated from the function (e.g., Network Address Translation (NAT), firewall) it controls. Refer to [RFC6887].
• PCP client denotes a PCP software instance responsible for issuing PCP requests to a PCP server. Refer to [RFC6887].

3. IP Address Selection

These steps specify the behavior to be followed by the PCP client to contact a PCP server when the PCP client has multiple IP addresses for a single PCP server. Additional considerations to be taken into account when the PCP client is multi-interfaced are specified in Section 4:

1. If the PCP client can use both address families when communicating to a particular PCP server, the PCP client SHOULD select the source address of the PCP request to be of the same IP address family as its requested PCP mapping (i.e., the address family of the Requested External IP Address).
2. Whenever communicating with a PCP server, the rules of Section 6 of [RFC6724] SHOULD be followed by using the source address selected in the previous step as input to the destination address selection algorithm.
3. The PCP client initializes its Maximum Retransmission Count (MRC) to 4.
4. The PCP client sends its PCP message to the PCP server's IP address following the retransmission procedure specified in Section 8.1.1 of [RFC6887]. If no response is received after MRC attempts, the PCP client re-tries the procedure excluding the destination addresses which did not respond. The PCP client SHOULD ignore any response received from an IP address after exhausting MRC attempts for that particular IP address. If, when sending PCP requests, the PCP client receives a hard ICMP error [RFC1122] it SHOULD immediately try the next IP address from the list of PCP server' IP addresses.
5. If the PCP client has exhausted all IP addresses configured for a given PCP server, the procedure is repeated every fifteen minutes until the PCP request is successfully answered.
6. Once the PCP client has successfully received a response from a PCP server's IP address, it sends subsequent PCP requests to the same server's IP address until that IP address becomes non-responsive, which causes the PCP client to follow the steps above to contact its PCP server.

For efficiency, the PCP client should use the same Mapping Nonce for requests sent to all PCP server' IP addresses.

If several PCP servers are configured, each with multiple IP addresses, the PCP client contacts all PCP servers in parallel following the steps described above. This procedure may result in a PCP client instantiating multiple mappings maintained by distinct PCP servers. The decision to use all these mappings or delete some of them is implementation-specific and only the PCP client can decide whether all mappings are needed or only a subset of them.

4. Multiple Interfaces

When an end host has multiple interfaces concurrently active (e.g., IEEE 802.11 and 3G), a PCP client would discover different PCP servers over different interfaces. A host may have multiple network interfaces (e.g, 3G, IEEE 802.11, etc.); each configured differently. Each PCP server learned MUST be associated with the interface via which it was learned. Particularly, the PCP client relies on the source IP address of an outgoing PCP request to select which PCP server(s) to use.

Although multiple interfaces may be available, a PCP client might choose to use just one based on, for example, cost and bandwidth requirements, and therefore would need to send PCP requests to just one PCP server.

Generic multi-interfaces considerations are documented in Section 8.4 of [RFC6887]

5. Example: Multiple PCP servers on a Single Interface

Figure 1 depicts an example that is used to illustrate the server selection procedure specified in Section 3.

                            ISP Network
                          |              |
    .........................................................
                          |              |        Subscriber Network
                  +-------+------+  +----+---------+
                  | PCP-Server-A |  | PCP-Server-B | 
                  |              |  |              |
                  +-------+------+  +----+---------+
         192.0.2.1        |              |     198.51.100.1
         2001:db8:2222::1 |              |     2001:db8:3333::1
                          |              |
                          |              |
                   -------+--------------+-----------
                                  |      
                                  |    203.0.113.0
                                  |    2001:db8:1111::1
                              +---+---+ 
                              | Host  | 
                              +-------+

                       ==================
                       |    Internet    |
                       ==================
                          |          |
                          |          | 
                     +----+-+      +-+----+
                     | ISP1 |      | ISP2 |               
                     +----+-+      +-+----+      ISP Network
                          |          |
    .........................................................
                          |          | 
                          |          |        Subscriber Network
                  +-------+---+ +----+------+
                  | rtr1 with | | rtr2 with | 
                  |   FW1     | |    FW2    |
                  +-------+---+ +----+------+
                          |          |
                          |          |
                   -------+----------+------
                               |
                           +---+---+ 
                           | Host  | 
                           +-------+

                     =====================
                     |    Internet       |
                     =====================
                        |              |
                        |              | 
                   +----+--------+   +-+------------+
                   | ISP1        |   | ISP2         |
                   |             |   |              |
                   +----+--------+   +-+------------+ ISP Network  
                        |              |               
                        |              |        
      ..............................................................
                        |              |
                        | Port1        | Port2    Subscriber Network
                        |              |                 
                   +----+-------------------+            
                   |rtr1: NAT & PCP servers |         
                   |       GW Router        |             
                   +----+-------------------+             
                        |                                
                        |    
                        |
                   -----+--------------
                        |
                      +-+-----+ 
                      | Host  |  (private address space)
                      +-------+