PCP Working Group M. Boucadair
Internet-Draft France Telecom
Updates: 6887 (if approved) R. Penno
Intended status: Standards Track D. Wing
Expires: January 22, 2015 P. Patil
T. Reddy
Cisco
July 21, 2014

PCP Server Selection
draft-ietf-pcp-server-selection-04

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/.

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This Internet-Draft will expire on January 22, 2015.

Copyright Notice

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

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Table of Contents

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. Refer to [I-D.boucadair-pcp-deployment-cases] for a discussion on PCP deployment scenarios.

If a PCP client discovers multiple PCP server IP addresses, it needs an indication to determine whether PCP entries are to be installed in all or a subset of discovered IP addresses. This document makes the following assumptions:

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:

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

This section describes the behavior of the PCP client 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 wildcard bound server, the candidate source addresses may be all IP addresses of the server or just the IP address on which the server intends to explicitly 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 to clears the cache of sorted destination address list 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 PCP server IP addresses.

4. IP Address Selection: Multiple PCP Servers

This section describes the behavior of the PCP client 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.

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 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)

Figure 1

Figure 1 depicts an example that is used to illustrate the server selection procedure specified in Section 3 and Section 4. In this example PCP servers (A and B) are co-located with edge routers (rtr1, rtr2) with each PCP server controlling its own device.

The example describes behavior when a single IP address for one PCP server is not responsive. The PCP client is configured with two PCP servers for the same interface, PCP-Server-A and PCP-Server-B each having two IP addresses, an IPv4 address and an IPv6 address. The PCP client wants an IPv4 mapping so it orders the addresses as follows:

Suppose that:

It sends two PCP requests at the same time, the first to 192.0.2.1 (corresponding to PCP-Server-A) and the second to 198.51.100.1 (corresponding to PCP-Server-B). The path to 198.51.100.1 is working so a PCP response is received. Because the path to 192.0.2.1 is broken, no PCP response is received. The PCP client retries 4 times to elicit a response from 192.0.2.1 and finally gives up on that address and sends a PCP message to 2001::db8:1111:1. That path is working, and a response is received. Thereafter, the PCP client should continue using that responsive IP address for PCP-Server-A (2001:db8:1111::1). In this particular case, it will have to use THIRD_PARTY option for IPv4 mappings.

6. Security Considerations

PCP related security considerations are discussed in [RFC6887].

This document does not specify how PCP server addresses are provisioned on the PCP client. It is the responsibility of PCP server provisioning document(s) to elaborate on security considerations to discover legitimate PCP servers.

7. IANA Considerations

This document does not request any action from IANA.

8. Acknowledgements

Many thanks to Dave Thaler, Simon Perreault, and Hassnaa Moustafa for their reviews and comments.

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.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A. and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, September 2012.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R. and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 2013.

9.2. Informative References

[I-D.boucadair-pcp-deployment-cases] Boucadair, M., "Port Control Protocol (PCP) Deployment Models", Internet-Draft draft-boucadair-pcp-deployment-cases-03, July 2014.
[RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989.
[RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B. and V. Gill, "IPv4 Multihoming Practices and Limitations", RFC 4116, July 2005.
[RFC7291] Boucadair, M., Penno, R. and D. Wing, "DHCP Options for the Port Control Protocol (PCP)", RFC 7291, July 2014.

Appendix A. Multi-homing

The main problem of a PCP multi-homing situation can be succinctly described as 'one PCP client, multiple PCP servers'. As described in Section 3, if a PCP client discovers multiple PCP servers, it should send requests to all of them with assumptions described in Section-1. The following sub-sections describe multi-homing examples to illustrate the PCP client behavior.

A.1. IPv6 Multi-homing

In this example of an IPv6 multi-homed network, two or more routers co-located with firewalls are present on a single link shared with the host(s). Each router is in turn connected to a different service provider network and the host in this environment would be offered multiple prefixes and advertised multiple DNS servers. Consider a scenario in which firewalls within an IPv6 multi-homing environment also implement a PCP server. The PCP client learns the available PCP servers using DHCP [RFC7291] or any other provisioning mechanism. In reference to Figure 2, a typical model is to embed DHCP servers in rtr1 and rtr2. A host located behind rtr1 and rtr2 can contact these two DHCP servers and retrieve from each server the IP address(es) of the corresponding PCP server.

The PCP client will send PCP requests in parallel to each of the PCP servers.

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

Figure 2: IPv6 Multihoming

A.2. IPv4 Multi-homing

In this example an IPv4 multi-homed network described in 'NAT- or RFC2260-based multi-homing' (Section 3.3 of [RFC4116]), the gateway router is connected to different service provider networks. This method uses Provider-Aggregatable (PA) addresses assigned by each transit provider to which the site is connected. The site uses NAT to translate the various provider addresses into a single set of private-use addresses within the site. In such a case, two PCP servers might have to be present to configure NAT to each of the transit providers. The PCP client learns the available PCP servers using DHCP [RFC7291] or any other provisioning mechanism. In reference to Figure 3, a typical model is to embed the DHCP server and the PCP servers in rtr1. A host located behind rtr1 can contact the DHCP server to obtain IP addresses of the PCP servers. The PCP client will send PCP requests in parallel to each of the PCP servers.

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

Figure 3: IPv4 Multihoming

Authors' Addresses

Mohamed Boucadair France Telecom Rennes, 35000 France EMail: mohamed.boucadair@orange.com
Reinaldo Penno Cisco USA EMail: repenno@cisco.com
Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, California 95134 USA EMail: dwing@cisco.com
Prashanth Patil Cisco Systems, Inc. Bangalore, India EMail: praspati@cisco.com
Tirumaleswar Reddy Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India EMail: tireddy@cisco.com