PCP Server Selection
draft-ietf-pcp-server-selection-08

Abstract

The document specifies the behavior to be followed by a 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 11, 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 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: PCP Server with Multiple IP Addresses
• 4. IP Address Selection: Multiple PCP Servers
• 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

1. Introduction

A host may have multiple network interfaces (e.g., 3G, IEEE 802.11, etc.); each configured with different PCP servers. Each PCP server learned must be associated with the interface on which it was learned. Generic multi-interface considerations are documented in Section 8.4 of [RFC6887]. Multiple PCP server 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. It is out of scope of this document to enumerate all deployment scenarios that require multiple PCP server IP addresses to be configured.

If a PCP client discovers multiple PCP server IP addresses, it needs to determine which actions it needs to undertake (e.g., whether PCP entries are to be installed in all or a subset of discovered IP addresses, whether some PCP entries are to be removed, etc.). This document makes the following assumptions:

• There is no requirement that multiple PCP servers configured on the same interface have the same capabilities.
• PCP requests to different PCP servers are independent, the result of a PCP request to one PCP server does not influence another.
• The configuration mechanism must distinguish IP addresses that belong to the same PCP server.

This document specifies the behavior to be followed by a PCP client [RFC6887] to contact its PCP server(s) [RFC6887] when it is configured with one or several PCP server IP addresses (e.g., using DHCP [RFC7291]).

2. Terminology

This document makes use of the following terms:

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

3. IP Address Selection: PCP Server with Multiple IP Addresses

This section describes the behavior a PCP client follows to contact its PCP server when the PCP client has multiple IP addresses for a single PCP server.

1. A PCP client should construct a set of candidate source addresses (Section 4 of [RFC6724]), based on application input and PCP [RFC6887] constraints. For example, when sending a PEER or a MAP with FILTER request for an existing TCP connection, the only candidate source address is the source address used for the existing TCP connection. But when sending a MAP request for a service that will accept incoming connections, the candidate source addresses may be all of the node's IP addresses, or some subset of IP addresses on which the service is configured to listen.
2. The PCP client then sorts the PCP server IP addresses as per Section 6 of [RFC6724] using the candidate source addresses 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 messages 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 with the next IP address in the sorted list. 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 SHOULD be repeated every fifteen (15) 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, all subsequent PCP requests to that PCP server are sent on the same IP address until that IP address becomes unresponsive. In case the IP address becomes unresponsive, the PCP client clears the cache of sorted destination addresses and follows the steps described above to contact the PCP server again.

For efficiency, the PCP client SHOULD use the same Mapping Nonce for requests sent to all IP addresses belonging to the same PCP server. As a reminder, nonce validation checks are performed when operating in the Simple Threat Model (Section 18.1 of [RFC6887]) to defend against some off-path attacks.

4. IP Address Selection: Multiple PCP Servers

This section describes the behavior a PCP client follows to contact multiple PCP servers, with each PCP server reachable on a list of IP addresses. There is no requirement that these multiple PCP servers have the same capabilities.

If several PCP servers are configured, each with multiple IP addresses, the PCP client contacts all PCP servers using the procedure described in Section 3.

As specified in Section 11.2 and Section 12.2 of [RFC6887], the PCP client must use a different Mapping Nonce for each PCP server it communicates with.

If the PCP client is configured, using some means, with the capabilities of each PCP server, a PCP client may choose to contact all PCP servers simultaneously or iterate through them with a delay.

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 depends on the purpose of the PCP request. For example, if the PCP servers are configuring firewall (not NAT) functionality then the client would by default (i.e., unless it knows that they all replicate state among them) need to use all the PCP servers.

5. Example: Multiple PCP Servers on a Single Interface

                               ISP Network
                             |              |
       .........................................................
                             |              |        Subscriber Network
                  +----------+-----+  +-----+----------+
                  | PCP-Server-A   |  | PCP-Server-B   |
                  |    (rtr1)      |  |   (rtr2)       |
                  +-------+--------+  +--+-------------+
         192.0.2.1        |              |     198.51.100.1
         2001:db8:1111::1 |              |     2001:db8:2222::1
                          |              |
                          |              |
                   -------+-------+------+-----------
                                  |      
                                  |    203.0.113.0
                                  |    2001:db8:3333::1
                              +---+---+ 
                              | Host  | 
                              +-------+

Edge Routers (rtr1, rtr2)

                       ==================
                       |    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)
                      +-------+