PCP T. Reddy Internet-Draft Cisco Intended status: Standards Track M. Isomaki Expires: March 20, 2013 Nokia D. Wing P. Patil Cisco September 16, 2012 Optimizing NAT and Firewall Keepalives Using Port Control Protocol (PCP) draft-reddy-pcp-optimize-keepalives-00 Abstract This document describes how Port Control Protocol is useful to reduce NAT and firewall keepalive messages for a variety of applications. 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 March 20, 2013. Copyright Notice Copyright (c) 2012 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 Reddy, et al. Expires March 20, 2013 [Page 1] Internet-Draft Optimize Keepalive with PCP September 2012 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 3 3.1. Application Scenarios . . . . . . . . . . . . . . . . . . 3 3.2. NAT and Firewall Topologies and Detection . . . . . . . . 5 3.3. Keepalive Optimization . . . . . . . . . . . . . . . . . . 6 4. Application-Specific Operation . . . . . . . . . . . . . . . . 6 4.1. SIP . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.3. Media and data channels with ICE . . . . . . . . . . . . . 8 4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . . 9 4.5. Firewall . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.5.1. IPv6 Network with Firewalls . . . . . . . . . . . . . 9 4.5.2. Mobile Network with Firewalls . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 8.2. Informative References . . . . . . . . . . . . . . . . . . 11 Appendix A. Example PHP script . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Reddy, et al. Expires March 20, 2013 [Page 2] Internet-Draft Optimize Keepalive with PCP September 2012 1. Introduction Many types of applications need to keep their Network Address Translator (NAT) and Firewall (FW) mappings alive for long periods of time, even when they are otherwise not sending or receiving any traffic. This is typically done by sending periodic keep-alive messages just to prevent the mappings from expiring. As NAT/FW mapping timers may be short and unknown to the endpoint, the frequency of these keep-alives may be high. An IPv4 or IPv6 host can use the Port Control Protocol (PCP)[I-D.ietf-pcp-base] to flexibly manage the IP address and port mapping information on NATs and FWs to facilitate communications with remote hosts. This document describes how PCP can be used to reduce keep-alive messages for both client- server and peer-to-peer type of communication. The mechanism described in this document is especially useful in cellular mobile networks, where frequent keep-alive messages make the radio transition between active and power-save states causing signaling congestion. The excessive time spent on the active state due to keep-alives also greatly reduces the battery life of the cellular connected devices such as smartphones or tablets. 2. Notational Conventions 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]. This note uses terminology defined in [RFC5245] and [I-D.ietf-pcp-base] . 3. Overview of Operation 3.1. Application Scenarios PCP can help both client-server and peer-to-peer applications to reduce their keep-alive rate. The relevant applications are the ones that need to keep their NAT/FW mappings alive for long periods of time, for instance to be able to send or receive application messages to both directions at any time. A typical client-server scenario is described in Figure 1. A client, who may reside behind one or multiple layers of NATs/FWs, opens a connection to a globally reachable server, and keeps it open to be able to receive messages from the server at any time. The connection may be a real transport connection using TCP or SCTP, or just an flow Reddy, et al. Expires March 20, 2013 [Page 3] Internet-Draft Optimize Keepalive with PCP September 2012 of UDP packets. Protocols operating in this manner include Session Initiation Protocol (SIP), Extensible Messaging and Presence Protocol (XMPP), Internet Mail Application Protocol (IMAP) with its IDLE command, the WebSocket protocol and the various HTTP long-polling protocols. There are also a number of proprietary instant messaging, Voice over IP, e-mail and notification delivery protocols that belong in this category. All of these protocols aim to keep the client- server connection alive for as long as the application is running. When the application has otherwise no traffic to send, specific keep- alive messages are sent periodically to ensure that the NAT/FW state in the middle does not expire. Instead of application keep-alives, the client can use PCP to keep up the required mapping at the NAT/FW. PCP PCP Client Server __________ +-----------+ +------+ / \ +-----------+ |Application|___| NAT/ |____| Internet |___|Application| | Client | | FW | | | | Server | +-----------+ +------+ \__________/ +-----------+ (multiple layers) ------------> PCP -----------------------------------------> Application keep-alive Figure 1: PCP with Client-Server applications There are also scenarios where the long-term communication association is between two peers, both of whom may reside behind a (layers of) NAT/FW. This is depicted in Figure 2. The initiation of the association may have happened using mechanisms such as Interactive Communications Establishment (ICE), perhaps first triggered by a "signaling" protocol such as SIP or XMPP or RTCWeb. Examples of the peer-to-peer protocols include RTP and RTCWeb data channel. A number of proprietary VoIP or video call or streaming or file transfer protocols also exist in this category. Typically the communication is based on UDP, but TCP or SCTP may be used. Unless there is no traffic flowing otherwise, the peers have to inject periodic keep-alive packets to keep the NAT/FW mappings on both sides of the communication active. Instead of application keep-alives, both peers can use PCP to control the mappings on the NAT/FWs in front of them. Reddy, et al. Expires March 20, 2013 [Page 4] Internet-Draft Optimize Keepalive with PCP September 2012 PCP PCP PCP PCP Client Server __________ Server Client +-----------+ +------+ / \ +------+ +-----------+ |Application|___| NAT/ |____| Internet |___| NAT/ |___|Application| | Peer | | FW | | | | FW | | Peer | +-----------+ +------+ \__________/ +------+ +-----------+ (multiple (multiple layers) layers) ------------> PCP PCP <------------ <---------------------------------------------------> Application keep-alive Figure 2: PCP with Peer-to-Peer applications 3.2. NAT and Firewall Topologies and Detection Before an application can reduce its keep-alive rate, it has to make sure it has all of the NATs and Firewalls on its path under control. This means it has to detect the presence of any PCP-unaware NATs and Firewalls on its path. PCP itself is able to detect unexpected NATs between the PCP client and server as depicted in Figure 3. The PCP client includes its own IP address and UDP port within the PCP request. The PCP server compares them to the source IP address and UDP port it sees on the packet. If they are differ, there are one or more additional NATs between the PCP client and server, and the server will return an error. Unless the application has some other means to control these PCP unaware NATs, it has to fall back to its default keep-alive mechanism. PCP PCP PCP Client Unaware Aware __________ +-----------+ +------+ +------+ / \ +-----------+ |Application|___| NAT |___| NAT/ |____| Internet |___|Application| | Client | | | | FW | | | | Server | +-----------+ +------+ +------+ \__________/ +-----------+ <-----------///----------> PCP based detection Figure 3: PCP unaware NAT between PCP client and server Reddy, et al. Expires March 20, 2013 [Page 5] Internet-Draft Optimize Keepalive with PCP September 2012 Figure 4 shows a topology where one or more PCP unaware NATs are deployed on the exterior of the PCP capable NAT/FWs. To detect this, the application must have the capability to request from its server or peer what IP and transport address it sees. If those differ from the IP and transport address given to the application by the out most PCP aware NAT/FW, the application can detect that there is at least one more PCP unaware NAT on the path. In this case, the application has to fall back to its default keep-alive mechanism. PCP PCP PCP Client Aware Unaware __________ +-----------+ +------+ +------+ / \ +-----------+ |Application|___| NAT/ |___| NAT |____| Internet |___|Application| | Client | | FW | | | | | | Server | +-----------+ +------+ +------+ \__________/ +-----------+ <------------> PCP <---------------------///---------------------------> Application based detection Figure 4: PCP unaware NAT external to the last PCP aware NAT Section 4 describes how the detection works in a number of real application protocols. The caveat is that Firewalls can not be detected this way. 3.3. Keepalive Optimization If the application determines that all NATs and Firewalls on its path support PCP, it can start using PCP instead of its default keep- alives to maintain the NAT/FW state. It can use PCP PEER Request with Requested Lifetime set to appropriate value. The application may still send some application specific heartbeat messages end-to- end. 4. Application-Specific Operation This section describes how PCP is used with specific application protocols. Reddy, et al. Expires March 20, 2013 [Page 6] Internet-Draft Optimize Keepalive with PCP September 2012 4.1. SIP For connection-less transports the User Agent (UA) sends STUN Binding Request over the SIP flow as described in section 4.4.2 of [RFC5626]. The UA then learns External IP Address and Port using PEER request/ response. If the XOR-MAPPED-ADDRESS in the STUN Binding Response matches the external address and port provided by PCP PEER response then the UA optimizes the keepalive traffic as described in Section 3.3. There is no further need to send STUN Binding Requests over the SIP flow to keep the NAT binding alive. If the XOR-MAPPED-ADDRESS in the STUN Binding Response does not match the external address and port provided by PCP PEER response then PCP will not be used to keep the NAT bindings alive for the flow that is being used for the SIP traffic. This means that multiple layers of NAT are involved and intermediate NATs are not PCP aware. In this case UA will continue to use the technique in section 4.4.2 of [RFC5626]. For connection-oriented transport, the UA sends STUN Binding Request multiplexed with SIP over the TCP connection. STUN multiplexed with other data over a TCP or TLS-over-TCP connection is explained in section 7.2.2 of [RFC5389]. UA then learns the External IP address and port using PEER request/response. If the XOR-MAPPED-ADDRESS in the STUN Binding Response matches the external address and port provided by PCP PEER response then the UA optimizes the keepalive traffic as described in Section 3.3. If the XOR-MAPPED-ADDRESS in the STUN Binding Response does not match the external address and port provided by PCP PEER response then PCP will not be used to keep the NAT bindings alive. In this case UA performs keep-alive check by sending a double-CRLF (the "ping") then waits to receive a single CRLF (the "pong") using the technique in section 4.4.1 of [RFC5626]. 4.2. HTTP Web Applications that require persistent connections use techniques such as HTTP long polling and Websockets for session keep alive as explained in section 3.1 of [I-D.isomaki-rtcweb-mobile]. In such scenarios, after the client establishes a connection with the HTTP server, it can execute server side scripts such as PHP residing on the server to provide the transport address and port of the HTTP client seen at the HTTP server. In addition, the HTTP client also learns the external IP Address and port using PCP PEER request/ response. If the IP address and port learned from the server matches the Reddy, et al. Expires March 20, 2013 [Page 7] Internet-Draft Optimize Keepalive with PCP September 2012 external address and port provided by PCP PEER response then the HTTP client optimizes keepalive traffic as described in Section 3.3. If the IP address and port do not match then PCP will not be used to keep the NAT bindings alive for the flow that is being used for the HTTP traffic. This means that there are NATs between the PCP server and the HTTP server. The HTTP client will have to resort to use existing techniques for keep alive. Please see Appendix A for an example server side PHP script to obtain client source IP address. 4.3. Media and data channels with ICE ICE agent learns the External IP Address and Port using MAP request/ response. This candidate learnt through PCP is encoded in the ICE offer and answer just like the server reflexive candidate, If the server reflexive candidate and External IP address learnt using PCP are different. When using the Recommended Formula in section 4.1.2.1 of [RFC5245] to compute priority for the candidates learnt through PCP, ICE agent can use preference value greater than or equal to the server reflexive candidates. The ICE agent in addition to ICE connectivity checks and performs the following : The ICE agent checks if the XOR-MAPPED-ADDRESS from the STUN [RFC5389] Binding response received as part of ICE connectivity check matches the external address and port provided by PCP MAP response. 1. If the match is successful then PCP will be used to keep the NAT bindings alive. The ICE agent optimizes keepalive traffic by refreshing the mapping via new PCP MAP request containing information from the earlier PCP response. 2. If the match is not successful then PCP will not be used for keep NAT binding alive. ICE agent will use technique in section 4..4 of [RFC6263] to keep NAT bindings alive. This means that multiple layers of NAT are involved and intermediate NATs are not PCP aware. Some network operators deploying a PCP Server may allow PEER but not MAP. In such cases the ICE agent learns the external IP address and port using STUN binding request/response during ICE connectivity checks. The ICE agent also learns the external IP Address and port using PCP PEER request/response. If the IP address and port learned from STUN binding response matches the external address and port provided by PCP PEER response then the ICE agent optimizes keepalive Reddy, et al. Expires March 20, 2013 [Page 8] Internet-Draft Optimize Keepalive with PCP September 2012 traffic as described in Section 3.3. 4.4. Detecting Flow Failure Using the Rapid Recovery technique in section 14 of [I-D.ietf-pcp-base] PCP client upon receiving PCP ANNOUNCE from NAT device becomes aware that NAT has rebooted or lost its mapping state. PCP client issues new PCP requests to recreate any lost mapping state and thus reconstruct lost mapping fast enough that existing media, HTTP and SIP flows do not break. If the NAT state cannot be recovered the endpoint will find the new external address and port as part of Rapid Recovery technique in PCP itself and reestablish connection with the peer. In lieu of this mechanism if NAT reboots and loses its mapping state or when a NAT gateway has its external IP address changed so that its current mapping state becomes invalid, it may take several seconds before the endpoints realize that the connectivity is lost. 4.5. Firewall PCP allows applications to communicate with Firewall devices with PCP functionality to create mappings for incoming connections. In such cases PCP can be used by the endpoint to create explicit mapping on Firewall to permit inbound traffic and further use PCP to avoid sending keep-alives to keep the Firewall mappings alive. 4.5.1. IPv6 Network with Firewalls As part of the call setup, the endpoint would gather its host candidates and relayed candidate from a TURN server, send the candidates in the offer to the peer endpoint. On receiving the answer from the peer endpoint, PCP client sends PCP MAP request to create dynamic mapping in Firewall to permit ICE connectivity checks and subsequent media traffic from remote peer. 4.5.2. Mobile Network with Firewalls Mobile Networks are also making use of a Firewall to protect their customers from various attacks like downloading malicious content. The Firewall is usually configured to block all unknown inbound connections as explained in section 2.1 of [I-D.chen-pcp-mobile-deployment] . In such cases PCP can be used by Mobile devices to create explicit mapping on Firewall to permit inbound traffic and optimize the keepalive traffic as described in Section 3.3. This would result in saving of radio and power consumption of the Mobile device while protecting it from attacks. Reddy, et al. Expires March 20, 2013 [Page 9] Internet-Draft Optimize Keepalive with PCP September 2012 5. IANA Considerations None 6. Security Considerations Security considerations in [RFC5245]and [I-D.ietf-pcp-base] apply to this use. 7. Acknowledgements The authors would like to thank Basavaraj Patil for valuable input to the document. 8. References 8.1. Normative References [I-D.ietf-pcp-base] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", draft-ietf-pcp-base-26 (work in progress), June 2012. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, October 2008. [RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client- Initiated Connections in the Session Initiation Protocol (SIP)", RFC 5626, October 2009. [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for Keeping Alive the NAT Mappings Associated with RTP / RTP Control Protocol (RTCP) Flows", RFC 6263, June 2011. Reddy, et al. Expires March 20, 2013 [Page 10] Internet-Draft Optimize Keepalive with PCP September 2012 8.2. Informative References [I-D.chen-pcp-mobile-deployment] Chen, G., Cao, Z., Boucadair, M., Ales, V., and L. Thiebaut, "Analysis of Port Control Protocol in Mobile Network", draft-chen-pcp-mobile-deployment-01 (work in progress), July 2012. [I-D.isomaki-rtcweb-mobile] Isomaki, M., "RTCweb Considerations for Mobile Devices", draft-isomaki-rtcweb-mobile-00 (work in progress), July 2012. Appendix A. Example PHP script Connected to on port on Pacific Time

Your IP address is: , port Click here to also obtain information when connecting to port 81.

"; ??} ?> Authors' Addresses Tirumaleswar Reddy Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560103 India Email: tireddy@cisco.com Reddy, et al. Expires March 20, 2013 [Page 11] Internet-Draft Optimize Keepalive with PCP September 2012 Markus Isomaki Nokia Keilalahdentie 2-4 FI-02150 Espoo Finland Email: markus.isomaki@nokia.com Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, California 95134 USA Email: dwing@cisco.com Prashanth Patil Cisco Systems, Inc. Cessna Business Park, Varthur Hobli Sarjapur Marthalli Outer Ring Road Bangalore, Karnataka 560103 India Email: praspati@cisco.com Reddy, et al. Expires March 20, 2013 [Page 12]