Port Control Protocol (PCP) Anycast Addresses
draft-ietf-pcp-anycast-07

PCP working group                                              S. Kiesel
Internet-Draft                                   University of Stuttgart
Intended status: Standards Track                                R. Penno
Expires: February 28, 2016                           Cisco Systems, Inc.
                                                             S. Cheshire
                                                                   Apple
                                                         August 27, 2015

             Port Control Protocol (PCP) Anycast Addresses
                       draft-ietf-pcp-anycast-07

Abstract

   The Port Control Protocol (PCP) Anycast Addresses enable PCP clients
   to transmit signaling messages to their closest PCP-aware on-path
   NAT, Firewall, or other middlebox, without having to learn the IP
   address of that middlebox via some external channel.  This document
   establishes one well-known IPv4 address and one well-known IPv6
   address to be used as PCP Anycast Addresses.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on February 28, 2016.

Copyright Notice

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   document authors.  All rights reserved.

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   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  PCP Server Discovery based on well-known IP Address  . . . . .  4
     2.1.  PCP Discovery Client behavior  . . . . . . . . . . . . . .  4
     2.2.  PCP Discovery Server behavior  . . . . . . . . . . . . . .  4
   3.  Deployment Considerations  . . . . . . . . . . . . . . . . . .  5
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Registration of IPv4 Special Purpose Address . . . . . . .  6
     4.2.  Registration of IPv6 Special Purpose Address . . . . . . .  6
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
     5.1.  Information Leakage through Anycast  . . . . . . . . . . .  7
     5.2.  Hijacking of PCP Messages sent to Anycast Addresses  . . .  7
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   The Port Control Protocol (PCP) [RFC6887] provides a mechanism to
   control how incoming packets are forwarded by upstream devices such
   as Network Address Translator IPv6/IPv4 (NAT64), Network Address
   Translator IPv4/IPv4 (NAT44), and IPv6 and IPv4 firewall devices.
   Furthermore, it provides a mechanism to reduce application keep alive
   traffic [I-D.ietf-pcp-optimize-keepalives].  The PCP base protocol
   document [RFC6887] specifies the message formats used, but the
   address to which a client sends its request is either assumed to be
   the default router (which is appropriate in a typical single-link
   residential network) or has to be configured otherwise via some
   external mechanism, such as a configuration file or a DHCP option
   [RFC7291].

   This document follows a different approach: it establishes two well-
   known anycast addresses for the PCP Server, one IPv4 address and one
   IPv6 address.  These well-known addresses may be hard-coded into PCP
   clients.  PCP clients usually send PCP requests to these addresses if
   no other PCP server addresses are known or after communication
   attempts to such other addresses have failed.  The anycast addresses
   are allocated from pools of special-purpose IP addresses (see
   Section 4), in accordance with Section 3.4 of [RFC4085].  Yet, a
   means to disable or override these well-known addresses (e. g., a
   configuration file option) should be available in implementations.

   Using an anycast address is particularly useful in larger network
   topologies.  For example, if the PCP-enabled NAT/firewall function is
   not located on the client's default gateway, but further upstream in
   a Carrier-grade NAT (CGN), sending PCP requests to the default
   gateway's IP address will not have the desired effect.  When using a
   configuration file or the DHCP option to learn the PCP server's IP
   address, this file or the DHCP server configuration must reflect the
   network topology, and the router and CGN configuration.  This may be
   cumbersome to achieve and maintain.  If there is more than one
   upstream CGN and traffic is routed using a dynamic routing protocol
   such as OSPF, this approach may not be feasible at all, as it cannot
   provide timely information on which CGN to interact with.  In
   contrast, when using the PCP anycast address, the PCP request will
   travel through the network like any other packet, without any special
   support from DNS, DHCP, other routers, or anything else, until it
   reaches the PCP-capable device, which receives it, handles it, and
   sends back a reply.  A further advantage of using an anycast address
   instead of a DHCP option is, that the anycast address can be hard-
   coded into the application.  There is no need for an application
   programming interface for passing the PCP server's address from the
   operating system's DHCP client to the application.  For further
   discussion of deployment considerations see Section 3.

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2.  PCP Server Discovery based on well-known IP Address

2.1.  PCP Discovery Client behavior

   The PCP anycast addresses, as defined in Sections 4.1 and 4.2, are
   added after the default router list (for IPv4 and IPv6) to the list
   of PCP server(s) (see Section 8.1, step 2. of [RFC6887]).  This list
   is processed as specified in [RFC7488].

   Note: If, in some specific scenario, it was desirable to use only the
   anycast address (and not the default router), this could be achieved
   by putting the anycast address into the configuration file, or DHCP
   option, etc.

2.2.  PCP Discovery Server behavior

   A PCP Server can be configured to listen on the anycast address for
   incoming PCP requests.

   PCP responses are sent from that same IANA-assigned address (see
   Page 6 of [RFC1546] for further discussion).

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3.  Deployment Considerations

   For general recommendations regarding operation of anycast services
   see [RFC4786].  Architectural considerations of IP anycast are
   discussed in [RFC7094].

   In some deployment scenarios, using PCP anycasting may have certain
   limitations, which can be overcome by using additional mechanisms or
   by using other PCP server discovery methods instead, such as DHCP
   [RFC7291] or a configuration file.

   One important example is a network topology, in which a network is
   connected to one or more upstream network(s) via several parallel
   firewalls, each individually controlled by its own PCP server.  Even
   if all of these PCP servers are configured for anycasting, only one
   will receive the messages sent by a given client, depending on the
   state of the routing tables.

   As long as routing is always symmetric, i.e., all upstream and
   downstream packets from/to that client are routed through this very
   same firewall, communication will be possible as expected.  If there
   is a routing change, a PCP client using PCP anycasting might start
   interacting with a different PCP server.  From the PCP client's point
   of view this would be the same as a PCP server reboot and the client
   could detect it by examining the Epoch field during the next PCP
   response or ANNOUNCE message.  The client would re-establish the
   firewall rules and packet flows could resume.

   If, however, routing is asymmetric, upstream packets from a client
   traverse a different firewall than the downstream packets to that
   client.  Establishing policy rules in only one of these two firewalls
   by means of PCP anycasting will not have the desired result of
   allowing bi-directional connectivity.  One solution approach to
   overcome this problem is an implementation-specific mechanism to
   synchronize state between all firewalls at the border of a network,
   i.e., a PEER message sent to any of these PCP servers would establish
   rules in all firewalls.  Another approach would be to use a different
   discovery mechanism (e.g., DHCP or a configuration file) that allows
   a PCP client to acquire a list of all PCP servers controlling the
   parallel firewalls and configure each of them individually.

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4.  IANA Considerations

4.1.  Registration of IPv4 Special Purpose Address

   IANA is requested to assign a single IPv4 address from the
   192.0.0.0/24 prefix and register it in the IANA IPv4 Special-Purpose
   Address Registry [RFC6890].

   +----------------------+-------------------------------------------+
   | Attribute            | Value                                     |
   +----------------------+-------------------------------------------+
   | Address Block        | 192.0.0.???/32        (??? = TBD by IANA) |
   | Name                 | Port Control Protocol Anycast             |
   | RFC                  | This document, if approved          (TBD) |
   | Allocation Date      | Date of approval of this document   (TBD) |
   | Termination Date     | N/A                                       |
   | Source               | True                                      |
   | Destination          | True                                      |
   | Forwardable          | True                                      |
   | Global               | True                                      |
   | Reserved-by-Protocol | False                                     |
   +----------------------+-------------------------------------------+

4.2.  Registration of IPv6 Special Purpose Address

   IANA is requested to assign a single IPv6 address from the 2001:
   0000::/23 prefix and register it in the IANA IPv6 Special-Purpose
   Address Registry [RFC6890].

   +----------------------+-------------------------------------------+
   | Attribute            | Value                                     |
   +----------------------+-------------------------------------------+
   | Address Block        | 2001:0????????/128    (??? = TBD by IANA) |
   | Name                 | Port Control Protocol Anycast             |
   | RFC                  | This document, if approved          (TBD) |
   | Allocation Date      | Date of approval of this document   (TBD) |
   | Termination Date     | N/A                                       |
   | Source               | True                                      |
   | Destination          | True                                      |
   | Forwardable          | True                                      |
   | Global               | True                                      |
   | Reserved-by-Protocol | False                                     |
   +----------------------+-------------------------------------------+

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5.  Security Considerations

   In addition to the security considerations in [RFC6887], [RFC4786],
   and [RFC7094], two further security issues are considered here.

5.1.  Information Leakage through Anycast

   In a network without any border gateway, NAT or firewall that is
   aware of the PCP anycast address, outgoing PCP requests could leak
   out onto the external Internet, possibly revealing information about
   internal devices.

   Using an IANA-assigned well-known PCP anycast address enables border
   gateways to block such outgoing packets.  In the default-free zone,
   routers should be configured to drop such packets.  Such
   configuration can occur naturally via BGP messages advertising that
   no route exists to said address.

   Sensitive clients that do not wish to leak information about their
   presence can set an IP TTL on their PCP requests that limits how far
   they can travel towards the public Internet.  However, methods for
   choosing an appropriate TTL value, e.g., based on the assumed radius
   of the trusted network domain, is beyond the scope of this document.

5.2.  Hijacking of PCP Messages sent to Anycast Addresses

   The anycast addresses are treated by normal host operating systems
   just as normal unicast addresses, i.e., packets destined for an
   anycast address are sent to the default router for processing and
   forwarding.  Hijacking such packets in the first network segment
   would effectively require to impersonate the default router, e.g., by
   means of ARP spoofing in an Ethernet network.  If such attacks are a
   serious concern in a given scenario, much more severe consequences to
   other protocols have to be feared as well.  Therefore, adequate
   measures have to be taken to prevent spoofing attacks targeted at the
   default router.

   Once an anycast message is forwarded closer to the core network,
   routing will likely become subject to dynamic routing protocols such
   as OSPF or BGP.  Anycast messages could be hijacked by announcing
   counterfeited messages in these routing protocols.  But again, an
   attacker capable of performing these attacks could cause
   significantly more damage to other protocols and therefore adequate
   means should be taken to prevent these attacks.

   In addition to following best current practices in first hop security
   and routing protocol security, PCP authentication
   [I-D.ietf-pcp-authentication] may be useful in some scenarios.

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   However, the effort needed for a proper setup of this authentication
   mechanism (e.g., installing the right shared secrets or cryptograpic
   keys on all involved systems) may thwart the goal of fully automatic
   configuration by using PCP anycast.  Therefore, this approach may be
   less suitable for scenarios with high trust between the operator of
   the PCP-controlled middlebox and all users (e.g., a residential
   gateway used only by family members) or if there is anyway rather
   limited trust that the middlebox will behave correctly (e.g., the
   Wifi in an airport lounge).  In contrast, this scheme may be highly
   useful in scenarios with many users and a trusted network operator,
   such as a large corporate network or a university campus network,
   which uses several parallel NATs or firewalls to connect to the
   Internet.  Therefore, a thorough analysis of the benefits and costs
   of using PCP authentication in a given network scenario is
   recommended.

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6.  Acknowledgments

   The authors would like to thank the members of the PCP working group
   for contributions and feedback, in particular Mohamed Boucadair,
   Charles Eckel, Simon Perreault, Tirumaleswar Reddy, Markus Stenberg,
   Dave Thaler, and Dan Wing.

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7.  References

7.1.  Normative References

   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              April 2013.

   [RFC6890]  Cotton, M., Vegoda, L., Bonica, R., and B. Haberman,
              "Special-Purpose IP Address Registries", BCP 153,
              RFC 6890, April 2013.

   [RFC7488]  Boucadair, M., Penno, R., Wing, D., Patil, P., and T.
              Reddy, "Port Control Protocol (PCP) Server Selection",
              RFC 7488, March 2015.

7.2.  Informative References

   [I-D.ietf-pcp-authentication]
              Wasserman, M., Hartman, S., Zhang, D., and T. Reddy, "Port
              Control Protocol (PCP) Authentication Mechanism",
              draft-ietf-pcp-authentication-14 (work in progress),
              July 2015.

   [I-D.ietf-pcp-optimize-keepalives]
              Reddy, T., Patil, P., Isomaki, M., and D. Wing,
              "Optimizing NAT and Firewall Keepalives Using Port Control
              Protocol (PCP)", draft-ietf-pcp-optimize-keepalives-06
              (work in progress), May 2015.

   [RFC1546]  Partridge, C., Mendez, T., and W. Milliken, "Host
              Anycasting Service", RFC 1546, November 1993.

   [RFC4085]  Plonka, D., "Embedding Globally-Routable Internet
              Addresses Considered Harmful", BCP 105, RFC 4085,
              DOI 10.17487/RFC4085, June 2005,
              <http://www.rfc-editor.org/info/rfc4085>.

   [RFC4786]  Abley, J. and K. Lindqvist, "Operation of Anycast
              Services", BCP 126, RFC 4786, December 2006.

   [RFC7094]  McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
              "Architectural Considerations of IP Anycast", RFC 7094,
              DOI 10.17487/RFC7094, January 2014,
              <http://www.rfc-editor.org/info/rfc7094>.

   [RFC7291]  Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
              the Port Control Protocol (PCP)", RFC 7291, July 2014.

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Authors' Addresses

   Sebastian Kiesel
   University of Stuttgart Information Center
   Networks and Communication Systems Department
   Allmandring 30
   Stuttgart  70550
   Germany

   Email: ietf-pcp@skiesel.de

   Reinaldo Penno
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Email: repenno@cisco.com

   Stuart Cheshire
   Apple Inc.
   1 Infinite Loop
   Cupertino, California  95014
   USA

   Phone: +1 408 974 3207
   Email: cheshire@apple.com

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