draft-ietf-p2psip-rpr-11.original		draft-ietf-p2psip-rpr-12.original.txt
	P2PSIP N. Zong, Ed.		P2PSIP N. Zong
	Internet-Draft X. Jiang		Internet-Draft X. Jiang
	Intended status: Standards Track R. Even		Intended status: Standards Track R. Even
	Expires: April 24, 2014 Huawei Technologies		Expires: August 29, 2014 Huawei Technologies
	Y. Zhang		Y. Zhang
	CoolPad		CoolPad
	October 21, 2013		February 25, 2014
	An Extension to REsource LOcation And Discovery (RELOAD) Protocol to		An Extension to REsource LOcation And Discovery (RELOAD) Protocol to
	Support Relay Peer Routing		Support Relay Peer Routing
	draft-ietf-p2psip-rpr-11		draft-ietf-p2psip-rpr-12
	Abstract		Abstract
	This document proposes an optional extension to REsource LOcation And		This document proposes an optional extension to REsource LOcation And
	Discovery (RELOAD) protocol to support relay peer routing mode.		Discovery (RELOAD) protocol to support relay peer routing mode.
	RELOAD recommends symmetric recursive routing for routing messages.		RELOAD recommends symmetric recursive routing for routing messages.
	The new optional extension provides a shorter route for responses		The new optional extension provides a shorter route for responses
	reducing the overhead on intermediate peers and describes the		reducing the overhead on intermediate peers and describes the
	potential use cases where this extension can be used.		potential use cases where this extension can be used.
	skipping to change at page 1, line 39		skipping to change at page 1, line 39
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on April 24, 2014.		This Internet-Draft will expire on August 29, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2013 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
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	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
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	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3.1. RPR . . . . . . . . . . . . . . . . . . . . . . . . . . . 4		3.1. RPR . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3.2. Scenarios where RPR can be used . . . . . . . . . . . . . 5		3.2. Scenarios where RPR can be used . . . . . . . . . . . . . 5
	3.2.1. Managed or closed P2P systems . . . . . . . . . . . . 5		3.2.1. Managed or closed P2P systems . . . . . . . . . . . . 5
	3.2.2. Using bootstrap nodes as relay peers . . . . . . . . 5		3.2.2. Using bootstrap nodes as relay peers . . . . . . . . 6
	3.2.3. Wireless scenarios . . . . . . . . . . . . . . . . . 6		3.2.3. Wireless scenarios . . . . . . . . . . . . . . . . . 6
	4. Relationship between SRR and RPR . . . . . . . . . . . . . . 6		4. Relationship between SRR and RPR . . . . . . . . . . . . . . 6
	4.1. How RPR works . . . . . . . . . . . . . . . . . . . . . . 6		4.1. How RPR works . . . . . . . . . . . . . . . . . . . . . . 6
	4.2. How SRR and RPR work together . . . . . . . . . . . . . . 6		4.2. How SRR and RPR work together . . . . . . . . . . . . . . 6
	5. Comparison on cost of SRR and RPR . . . . . . . . . . . . . . 7		5. RPR extensions to RELOAD . . . . . . . . . . . . . . . . . . 7
	5.1. Closed or managed networks . . . . . . . . . . . . . . . 7		5.1. Basic requirements . . . . . . . . . . . . . . . . . . . 7
	5.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 7		5.2. Modification to RELOAD message structure . . . . . . . . 7
	6. RPR extensions to RELOAD . . . . . . . . . . . . . . . . . . 8		5.2.1. Extensive routing mode . . . . . . . . . . . . . . . 7
	6.1. Basic requirements . . . . . . . . . . . . . . . . . . . 8		5.3. Creating a request . . . . . . . . . . . . . . . . . . . 8
	6.2. Modification to RELOAD message structure . . . . . . . . 8		5.3.1. Creating a request for RPR . . . . . . . . . . . . . 8
	6.2.1. State-keeping flag . . . . . . . . . . . . . . . . . 8		5.4. Request and response processing . . . . . . . . . . . . . 8
	6.2.2. Extensive routing mode . . . . . . . . . . . . . . . 9		5.4.1. Destination peer: receiving a request and sending a
	6.3. Creating a request . . . . . . . . . . . . . . . . . . . 9		response . . . . . . . . . . . . . . . . . . . . . . 8
	6.3.1. Creating a request for RPR . . . . . . . . . . . . . 9		5.4.2. Sending peer: receiving a response . . . . . . . . . 9
	6.4. Request and response processing . . . . . . . . . . . . . 10		5.4.3. Relay peer processing . . . . . . . . . . . . . . . . 9
	6.4.1. Destination peer: receiving a request and sending a		6. Overlay configuration extension . . . . . . . . . . . . . . . 9
	response . . . . . . . . . . . . . . . . . . . . . . 10		7. Discovery of relay peers . . . . . . . . . . . . . . . . . . 10
	6.4.2. Sending peer: receiving a response . . . . . . . . . 11		8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
	6.4.3. Relay peer processing . . . . . . . . . . . . . . . . 11		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
	7. Overlay configuration extension . . . . . . . . . . . . . . . 11		10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
	8. Discovery of relay peers . . . . . . . . . . . . . . . . . . 11		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 11		11.1. Normative References . . . . . . . . . . . . . . . . . . 10
	10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12		11.2. Informative References . . . . . . . . . . . . . . . . . 11
	10.1. A new RELOAD Forwarding Option . . . . . . . . . . . . . 12		Appendix A. Optional methods to investigate peer connectivity . 11
	11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12		Appendix B. Comparison on cost of SRR and RPR . . . . . . . . . 12
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12		B.1. Closed or managed networks . . . . . . . . . . . . . . . 12
	12.1. Normative References . . . . . . . . . . . . . . . . . . 12		B.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 13
	12.2. Informative References . . . . . . . . . . . . . . . . . 12		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
	13. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
	Appendix A. Optional methods to investigate peer connectivity . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
	1. Introduction		1. Introduction
	REsource LOcation And Discovery (RELOAD) protocol [I-D.ietf-p2psip-		REsource LOcation And Discovery (RELOAD) protocol [RFC6940]
	base] recommends symmetric recursive routing (SRR) for routing		recommends symmetric recursive routing (SRR) for routing messages and
	messages and describes the extensions that would be required to		describes the extensions that would be required to support additional
	support additional routing algorithms. Other than SRR, two other		routing algorithms. Other than SRR, two other routing options:
	routing options: direct response routing (DRR) and relay peer routing		direct response routing (DRR) and relay peer routing (RPR) are also
	(RPR) are also discussed in Appendix A of [I-D.ietf-p2psip-base]. As		discussed in Appendix A of [RFC6940]. As we show in Section 3, RPR
	we show in section 3, RPR is advantageous over SRR in some scenarios		is advantageous over SRR in some scenarios reducing load (CPU and
	reducing load (CPU and link bandwidth) on intermediate peers. RPR		link bandwidth) on intermediate peers. RPR works better in a network
	works better in a network where relay peers are provisioned in		where relay peers are provisioned in advance so that relay peers are
	advance so that relay peers are publicly reachable in the P2P system.		publicly reachable in the P2P system. In other scenarios, using a
	In other scenarios, using a combination of RPR and SRR together is		combination of RPR and SRR together is more likely to bring benefits
	more likely to bring benefits than if SRR is used alone.		than if SRR is used alone.
	Note that in this document, we focus on RPR routing mode and its		Note that in this document, we focus on RPR routing mode and its
	extensions to RELOAD to produce a standalone solution. Please refer		extensions to RELOAD to produce a standalone solution. Please refer
	to DRR document [I-D.ietf-p2psip-drr] for DRR routing mode.		to DRR document [I-D.ietf-p2psip-drr] for DRR routing mode.
	We first discuss the problem statement in Section 3, then how to		We first discuss the problem statement in Section 3, then how to
	combine RPR and SRR is presented in Section 4. In Section 5, we give		combine RPR and SRR is presented in Section 4. An extension to
	comparison on the cost of SRR and RPR in both managed and open		RELOAD to support RPR is defined in Section 5. Discovery of relay
	networks. An extension to RELOAD to support RPR is proposed in		peers is introduced in Section 6. Some optional methods to check
	Section 6. Discovery of relay peers is introduced in Section 7.		peer connectivity are introduced in Appendix A. In Appendix B, we
	Some optional methods to check peer connectivity are introduced in		give comparison on the cost of SRR and RPR in both managed and open
	Appendix A.		networks.
	2. Terminology		2. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	We use the terminology and definitions from the RELOAD base draft		We use the terminology and definitions from the RELOAD base draft
	[I-D.ietf-p2psip-base] extensively in this document. We also use		[RFC6940] extensively in this document. We also use terms defined in
	terms defined in NAT behavior discovery [RFC5780]. Other terms used		NAT behavior discovery [RFC5780]. Other terms used in this document
	in this document are defined inline when used and are also defined		are defined inline when used and are also defined below for
	below for reference.		reference.
	Publicly Reachable: A peer is publicly reachable if it can receive		Publicly Reachable: A peer is publicly reachable if it can receive
	unsolicited messages from any other peer in the same overlay.		unsolicited messages from any other peer in the same overlay.
	Note: "publicly" does not mean that the peers must be on the		Note: "publicly" does not mean that the peers must be on the
	public Internet, because the RELOAD protocol may be used in a		public Internet, because the RELOAD protocol may be used in a
	closed network.		closed network.
	Relay Peer: A type of publicly reachable peer that can receive		Relay Peer: A type of publicly reachable peer that can receive
	unsolicited messages from all other peers in the overlay and		unsolicited messages from all other peers in the overlay and
	forward the responses from destination peers towards the sender of		forward the responses from destination peers towards the sender of
	skipping to change at page 4, line 21		skipping to change at page 4, line 18
	responses to P2PSIP requests are sent by the destination peer to a		responses to P2PSIP requests are sent by the destination peer to a
	relay peer transport address who will forward the responses		relay peer transport address who will forward the responses
	towards the sending peer. For simplicity, the abbreviation RPR is		towards the sending peer. For simplicity, the abbreviation RPR is
	used instead in the rest of the document.		used instead in the rest of the document.
	Symmetric Recursive Routing (SRR): refers to a routing mode in		Symmetric Recursive Routing (SRR): refers to a routing mode in
	which responses follow the reverse path of the request to get to		which responses follow the reverse path of the request to get to
	the sending peer. For simplicity, the abbreviation SRR is used		the sending peer. For simplicity, the abbreviation SRR is used
	instead in the rest of the document.		instead in the rest of the document.
			Direct Response Routing (DRR): refers to a routing mode in which
			responses to P2PSIP requests are returned to the sending peer
			directly from the destination peer based on the sending peer's own
			local transport address(es). For simplicity, the abbreviation DRR
			is used instead in the rest of the document.
	3. Overview		3. Overview
	RELOAD is expected to work under a great number of application		RELOAD is expected to work under a great number of application
	scenarios. The situations where RELOAD is to be deployed differ		scenarios. The situations where RELOAD is to be deployed differ
	greatly. For instance, some deployments are global, such as a Skype-		greatly. For instance, some deployments are global, such as a Skype-
	like system intended to provide public service, while others run in		like system intended to provide public service, while others run in
	closed networks of small scale. SRR works in any situation, but RPR		closed networks of small scale. SRR works in any situation, but RPR
	may work better in some specific scenarios.		may work better in some specific scenarios.
	3.1. RPR		3.1. RPR
	skipping to change at page 4, line 49		skipping to change at page 5, line 5
	If peer A knows it is behind a NAT or NATs, and knows one or more		If peer A knows it is behind a NAT or NATs, and knows one or more
	relay peers with whom they have a prior connections, peer A can try		relay peers with whom they have a prior connections, peer A can try
	RPR. Assume A is associated with relay peer R. When sending the		RPR. Assume A is associated with relay peer R. When sending the
	request, peer A includes information describing peer R transport		request, peer A includes information describing peer R transport
	address in the request. When peer X receives the request, peer X		address in the request. When peer X receives the request, peer X
	sends the response to peer R, which forwards it directly to Peer A on		sends the response to peer R, which forwards it directly to Peer A on
	the existing connection. Figure 1 illustrates RPR. Note that RPR		the existing connection. Figure 1 illustrates RPR. Note that RPR
	also allows a shorter route for responses compared to SRR, which		also allows a shorter route for responses compared to SRR, which
	means less overhead on intermediate peers. Establishing a connection		means less overhead on intermediate peers. Establishing a connection
	to the relay with TLS requires multiple round trips. Please refer to		to the relay with TLS requires multiple round trips. Please refer to
	Section 5 for cost comparison between SRR and RPR.		Appendix B for cost comparison between SRR and RPR.
	A B C D X R		A B C D X R
	| Request | | | | |		| Request | | | | |
	|----------->| | | | |		|----------->| | | | |
	| | Request | | | |		| | Request | | | |
	| |----------->| | | |		| |----------->| | | |
	| | | Request | | |		| | | Request | | |
	| | |----------->| | |		| | |----------->| | |
	| | | | Request | |		| | | | Request | |
	| | | |----------->| |		| | | |----------->| |
	skipping to change at page 6, line 28		skipping to change at page 6, line 31
	4.1. How RPR works		4.1. How RPR works
	Peers using RPR MUST maintain a connection with their relay peer(s).		Peers using RPR MUST maintain a connection with their relay peer(s).
	This can be done in the same way as establishing a neighbor		This can be done in the same way as establishing a neighbor
	connection between peers by using the Attach method.		connection between peers by using the Attach method.
	A requirement for RPR is for the source peer to convey their relay		A requirement for RPR is for the source peer to convey their relay
	peer (or peers) transport address in the request, so the destination		peer (or peers) transport address in the request, so the destination
	peer knows where the relay peer are and send the response to a relay		peer knows where the relay peer are and send the response to a relay
	peer first. The request SHOULD include also the requesting peer		peer first. The request MUST include also the requesting peer node
	information enabling the relay peer to route the response back to the		ID or IP address enabling the relay peer to route the response back
	right peer.		to the right peer.
	Note that being a relay peer does not require that the relay peer has		Note that being a relay peer does not require that the relay peer has
	more functionality than an ordinary peer. As discussed later, relay		more functionality than an ordinary peer. As discussed later, relay
	peers comply with the same procedure as an ordinary peer to forward		peers comply with the same procedure as an ordinary peer to forward
	messages. The only difference is that there may be a larger traffic		messages. The only difference is that there may be a larger traffic
	burden on relay peers. Relay peers can decide whether to accept a		burden on relay peers. Relay peers can decide whether to accept a
	new connection based on their current burden.		new connection based on their current burden.
	4.2. How SRR and RPR work together		4.2. How SRR and RPR work together
	RPR is not intended to replace SRR. It is better to use these two		RPR is not intended to replace SRR. It is better to use these two
	modes together to adapt to each peer's specific situation. Note that		modes together to adapt to each peer's specific situation. Note that
	the informative suggestions on how to transition between SRR and RPR		the informative suggestions on how to transition between SRR and RPR
	are the same with that of DRR. Please refer to DRR document [I-D		are the same with that of DRR. Please refer to Section 4.2 of DRR
	.ietf-p2psip-drr] for more details. If a relay peer is provided by		document [I-D.ietf-p2psip-drr] for more details. If a relay peer is
	the service provider, peers MAY prefer RPR over SRR. Otherwise,		provided by the service provider, peers SHOULD prefer RPR over SRR.
	using RPR SHOULD be discouraged in the open Internet or if the		Otherwise, using RPR SHOULD not be used in the open Internet or if
	administrator does not feel he have enough information about the		the administrator does not feel he have enough information about the
	overlay. A new overlay configuration element specifying the usage of		overlay. A new overlay configuration element specifying the usage of
	DRR is defined in Section 7.		DRR is defined in Section 6.
	5. Comparison on cost of SRR and RPR
	The major advantage of the use of RPR is that it reduces the number
	of intermediate peers traversed by the response. By doing that, it
	reduces the load on those peers' resources like processing and
	communication bandwidth.
	5.1. Closed or managed networks
	As described in Section 3, many P2P systems run in a closed or
	managed environment (e.g., carrier networks) so that network
	administrators would know that they could safely use RPR.
	The number of hops for a response in SRR and RPR are listed in the
	following table. Note that the same illustrative settings can be
	found in DRR document [I-D.ietf-p2psip-drr].
	Mode | Success | No. of Hops | No. of Msgs
	----------------------------------------------------
	SRR | Yes | log(N) | log(N)
	RPR | Yes | 2 | 2
	RPR(DTLS) | Yes | 2 | 7+2
	Table 1. Comparison of SRR and RPR in closed networks
	From the above comparison, it is clear that:
	1) In most cases when N > 4 (2^2), RPR uses fewer hops than SRR.
	Using a shorter route means less overhead and resource usage on
	intermediate peers, which is an important consideration for adopting
	RPR in the cases where the resources such as CPU and bandwidth are
	limited, e.g., the case of mobile, wireless networks.
	2) In the cases when N > 512 (2^9), RPR also uses fewer messages than
	SRR.
	3) In the cases when N < 512, RPR uses more messages than SRR (but
	still uses fewer hops than SRR). So the consideration on whether
	using RPR or SRR depends on other factors like using less resources
	(bandwidth and processing) from the intermediate peers. Section 4
	provides use cases where RPR has better chance to work or where the
	intermediary resources considerations are important.
	5.2. Open networks
	In open networks (e.g., Internet) where RPR is not guaranteed to
	work, RPR can fall back to SRR if it fails after trial, as described
	in Section 4. Based on the same settings of Section 5.1, the number
	of hops, number of messages for a response in SRR and RPR are listed
	in the following table.
	Mode | Success | No. of Hops | No. of Msgs
	-----------------------------------------------------------
	SRR | Yes | log(N) | log(N)
	RPR | Yes | 2 | 2
	| Fail&Fall back to SRR | 2+log(N)| 2+log(N)
	RPR(DTLS) | Yes | 2 | 7+2
	| Fail&Fall back to SRR | 2+log(N)| 9+log(N)
	Table 2. Comparison of SRR and RPR in open networks
	From the above comparison, it can be observed that trying to first
	use RPR could still provide an overall number of hops lower than
	directly using SRR. The detailed analysis is same as DRR case and
	can be found in DRR document [I-D.ietf-p2psip-drr].
	6. RPR extensions to RELOAD		5. RPR extensions to RELOAD
	Adding support for RPR requires extensions to the current RELOAD		Adding support for RPR requires extensions to the current RELOAD
	protocol. In this section, we define the extensions required to the		protocol. In this section, we define the extensions required to the
	protocol, including extensions to message structure and to message		protocol, including extensions to message structure and to message
	processing.		processing.
	6.1. Basic requirements		5.1. Basic requirements
	All peers MUST be able to process requests for routing in SRR, and		All peers MUST be able to process requests for routing in SRR, and
	MAY support RPR routing requests.		MAY support RPR routing requests.
	6.2. Modification to RELOAD message structure		5.2. Modification to RELOAD message structure
	RELOAD provides an extensible framework to accommodate future		RELOAD provides an extensible framework to accommodate future
	extensions. In this section, we define a ForwardingOption structure		extensions. In this section, we define an RPR routing option to the
	and present a state-keeping flag to support RPR mode.		extensive routing mode specified in [DRR]. The state-keeping flag
			from [DRR] is needed to support RPR mode.
	6.2.1. State-keeping flag
	flag : 0x08 IGNORE-STATE-KEEPING
	If IGNORE-STATE-KEEPING is set, any peer receiving this message and
	which is not the destination of the message SHOULD forward the
	message with the full via_list and SHOULD NOT maintain any internal
	state.
	6.2.2. Extensive routing mode
	We first define a new type to define the new option,		5.2.1. Extensive routing mode
	extensive_routing_mode:
	The option value is illustrated as below, defining the		The new RouteMode value for RPR is defined below for the
	ExtensiveRoutingModeOption structure:		ExtensiveRoutingModeOption structure:
	enum {(0),DRR(1),RPR(2),(255)} RouteMode;		enum {(0),DRR(1),RPR(2),(255)} RouteMode;
	struct {		struct {
	RouteMode routemode;		RouteMode routemode;
	OverlayLinkType transport;		OverlayLinkType transport;
	IpAddressPort ipaddressport;		IpAddressPort ipaddressport;
	Destination destinations<1..2^8-1>;		Destination destinations<1..2^8-1>;
	} ExtensiveRoutingModeOption;		} ExtensiveRoutingModeOption;
	skipping to change at page 9, line 38		skipping to change at page 8, line 9
	deliver responses from the destination peer to the relay peer.		deliver responses from the destination peer to the relay peer.
	IpAddressPort: refers to the transport address that the destination		IpAddressPort: refers to the transport address that the destination
	peer should use to send the response to. This will be a relay peer		peer should use to send the response to. This will be a relay peer
	address for RPR.		address for RPR.
	Destination: refers to the relay peer itself. If the routing mode is		Destination: refers to the relay peer itself. If the routing mode is
	RPR, then the destination contains two destinations, which are the		RPR, then the destination contains two destinations, which are the
	relay peer's Node-ID and the sending peer's Node-ID.		relay peer's Node-ID and the sending peer's Node-ID.
	6.3. Creating a request		5.3. Creating a request
	6.3.1. Creating a request for RPR		5.3.1. Creating a request for RPR
	When using RPR for a transaction, the sending peer MUST set the		When using RPR for a transaction, the sending peer MUST set the
	IGNORE-STATE-KEEPING flag in the ForwardingHeader. Additionally, the		IGNORE-STATE-KEEPING flag in the ForwardingHeader. Additionally, the
	peer MUST construct and include a ForwardingOptions structure in the		peer MUST construct and include a ForwardingOptions structure in the
	ForwardingHeader. When constructing the ForwardingOption structure,		ForwardingHeader. When constructing the ForwardingOption structure,
	the fields MUST be set as follows:		the fields MUST be set as follows:
	1) The type MUST be set to extensive_routing_mode.		1) The type MUST be set to extensive_routing_mode.
	2) The ExtensiveRoutingModeOption structure MUST be used for the		2) The ExtensiveRoutingModeOption structure MUST be used for the
	skipping to change at page 10, line 21		skipping to change at page 8, line 37
	2.2) transport set as appropriate for the relay peer.		2.2) transport set as appropriate for the relay peer.
	2.3) ipaddressport set to the transport address of the relay peer		2.3) ipaddressport set to the transport address of the relay peer
	that the sender wishes the message to be relayed through.		that the sender wishes the message to be relayed through.
	2.4) destination structure MUST contain two values. The first MUST		2.4) destination structure MUST contain two values. The first MUST
	be defined as type node and set with the values for the relay peer.		be defined as type node and set with the values for the relay peer.
	The second MUST be defined as type node and set with the sending		The second MUST be defined as type node and set with the sending
	peer's own values.		peer's own values.
	6.4. Request and response processing		5.4. Request and response processing
	This section gives normative text for message processing after RPR is		This section gives normative text for message processing after RPR is
	introduced. Here, we only describe the additional procedures for		introduced. Here, we only describe the additional procedures for
	supporting RPR. Please refer to [I-D.ietf-p2psip-base] for RELOAD		supporting RPR. Please refer to [RFC6940] for RELOAD base
	base procedures.		procedures.
	6.4.1. Destination peer: receiving a request and sending a response		5.4.1. Destination peer: receiving a request and sending a response
	When the destination peer receives a request, it will check the		When the destination peer receives a request, it will check the
	options in the forwarding header. If the destination peer can not		options in the forwarding header. If the destination peer can not
	understand extensive_routing_mode option in the request, it MUST		understand extensive_routing_mode option in the request, it MUST
	attempt using SRR to return an "Error_Unknown_Extension" response		attempt using SRR to return an "Error_Unknown_Extension" response
	(defined in Section 6.3.3.1 and Section 14.9 of [I-D.ietf-p2psip-		(defined in Section 6.3.3.1 and Section 14.9 of [RFC6940]) to the
	base]) to the sending peer.		sending peer.
	If the routing mode is RPR, the destination peer MUST construct a		If the routing mode is RPR, the destination peer MUST construct a
	destination_list for the response with two entries. The first MUST		destination_list for the response with two entries as defined in
	be set to the relay peer Node-ID from the option in the request and		[RFC6940]. The first MUST be set to the relay peer Node-ID from the
	the second MUST be the sending peer Node-ID from the option of the		option in the request and the second MUST be the sending peer Node-ID
	request.		from the option of the request.
	In the event that the routing mode is set to RPR and there are not		In the event that the routing mode is set to RPR and there are not
	exactly two destinations, the destination peer MUST try to send an		exactly two destinations, the destination peer MUST try to send an
	"Error_Unknown_Extension" response (defined in Section 6.3.3.1 and		"Error_Unknown_Extension" response (defined in Section 6.3.3.1 and
	Section 14.9 of [I-D.ietf-p2psip-base]) to the sending peer using		Section 14.9 of [RFC6940]) to the sending peer using SRR.
	SRR.
	After the peer constructs the destination_list for the response, it		After the peer constructs the destination_list for the response, it
	sends the response to the transport address which is indicated in the		sends the response to the transport address which is indicated in the
	ipaddressport field in the option using the specific transport mode		ipaddressport field in the option using the specific transport mode
	in the Forwardingoption. If the destination peer receives a		in the Forwardingoption. If the destination peer receives a
	retransmit with SRR preference on the message it is trying to		retransmit with SRR preference on the message it is trying to
	response to now, the responding peer SHOULD abort the RPR response		response to now, the responding peer SHOULD abort the RPR response
	and use SRR.		and use SRR.
	6.4.2. Sending peer: receiving a response		5.4.2. Sending peer: receiving a response
	Upon receiving a response, the peer follows the rules in [I-D.ietf-		Upon receiving a response, the peer follows the rules in [RFC6940].
	p2psip-base]. If the sender used RPR and does not get a response		If the sender used RPR and does not get a response until the timeout,
	until the timeout, it MAY either resend the message using RPR but		it MAY either resend the message using RPR but with a different relay
	with a different relay peer (if available), or resend the message		peer (if available), or resend the message using SRR.
	using SRR.
	6.4.3. Relay peer processing		5.4.3. Relay peer processing
	Relay peers are designed to forward responses to peers who are not		Relay peers are designed to forward responses to peers who are not
	publicly reachable. For the routing of the response, this document		publicly reachable. For the routing of the response, this document
	still uses the destination_list. The only difference from SRR is		still uses the destination_list. The only difference from SRR is
	that the destination_list is not the reverse of the via_list.		that the destination_list is not the reverse of the via_list.
	Instead, it is constructed from the forwarding option as described		Instead, it is constructed from the forwarding option as described
	below.		below.
	When a relay peer receives a response, it MUST follow the rules in		When a relay peer receives a response, it MUST follow the rules in
	[I-D.ietf-p2psip-base]. It receives the response, validates the		[RFC6940]. It receives the response, validates the message, re-
	message, re-adjust the destination_list and forward the response to		adjust the destination_list and forward the response to the next hop
	the next hop in the destination_list based on the connection table.		in the destination_list based on the connection table. There is no
	There is no added requirement for relay peer.		added requirement for relay peer.
	7. Overlay configuration extension		6. Overlay configuration extension
	This document uses the new RELOAD overlay configuration element,		This document uses the new RELOAD overlay configuration element,
	"route-mode", inside each "configuration" element, as defined in		"route-mode", inside each "configuration" element, as defined in
	Section 7 of the DRR document [I-D.ietf-p2psip-drr].		Section 6 of the DRR document [I-D.ietf-p2psip-drr]. The route mode
			MUST be "RPR".
	8. Discovery of relay peers		7. Discovery of relay peers
	There are several ways to distribute the information about relay		There are several ways to distribute the information about relay
	peers throughout the overlay. P2P network providers can deploy some		peers throughout the overlay. P2P network providers can deploy some
	relay peers and advertise them in the configuration file. With the		relay peers and advertise them in the configuration file. With the
	configuration file at hand, peers can get relay peers to try RPR.		configuration file at hand, peers can get relay peers to try RPR.
	Another way is to consider relay peer as a service and then some		Another way is to consider relay peer as a service and then some
	service advertisement and discovery mechanism can also be used for		service advertisement and discovery mechanism can also be used for
	discovering relay peers, for example, using the same mechanism as		discovering relay peers, for example, using the same mechanism as
	used in TURN server discovery in base RELOAD [I-D.ietf-p2psip-base].		used in TURN server discovery in base RELOAD [RFC6940]. Another
	Another option is to let a peer advertise its capability to be a		option is to let a peer advertise its capability to be a relay in the
	relay in the response to ATTACH or JOIN.		response to ATTACH or JOIN.
	9. Security Considerations		8. Security Considerations
	The normative security recommendations of Section 13 of base draft
	[I-D.ietf-p2psip-base] are applicable to this document. As a routing
	alternative, the security part of RPR conforms to Section 13.6 of the
	base draft which describes routing security. RPR behaves like a DRR
	requesting node towards the destination node. The RPR relay node is
	not an arbitrary node but SHOULD be a trusted one (managed network,
	bootstrap nodes or configured relay) which will make it less of a
	risk as outlined in section13 of the based draft.
	10. IANA Considerations		The normative security recommendations of Section 13 of base draft
			[RFC6940] are applicable to this document. As a routing alternative,
			the security part of RPR conforms to Section 13.6 of the base draft
			which describes routing security. RPR behaves like a DRR requesting
			node towards the destination node. The RPR relay node may be not an
			arbitrary node, for example, managed network, bootstrap nodes or
			configured relay which will make it less of a risk as outlined in
			Section 13 of the based draft [RFC6940].
	10.1. A new RELOAD Forwarding Option		In order to address possible DOS attacks, the relay SHOULD also limit
			the number of maximum connections, this is required also to reduce to
			load on the relay as explained in Section 4.1.
	A new RELOAD Forwarding Option type is added to the Forwarding Option		9. IANA Considerations
	Registry defined in [I-D.ietf-p2psip-base].
	Type: 0x02 - extensive_routing_mode		No IANA update.
	11. Acknowledgments		10. Acknowledgments
	David Bryan has helped extensively with this document, and helped		David Bryan has helped extensively with this document, and helped
	provide some of the text, analysis, and ideas contained here. The		provide some of the text, analysis, and ideas contained here. The
	authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti		authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti
	Lakshminath, Bruce Lowekamp, Stephane Bryant, Marc Petit-Huguenin and		Lakshminath, Bruce Lowekamp, Stephane Bryant, Marc Petit-Huguenin and
	Carlos Jesus Bernardos Cano for their constructive comments.		Carlos Jesus Bernardos Cano for their constructive comments.
	12. References		11. References
	12.1. Normative References		11.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC2119, March 1997.		Requirement Levels", BCP 14, RFC2119, March 1997.
	[I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E.,		[RFC6940] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and H.
	Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery		Schulzrinne, "REsource LOcation And Discovery (RELOAD) Base
	(RELOAD) Base Protocol", draft-ietf-p2psip-base-26 (work in		Protocol", RFC6940, January 2014.
	progress), February 2013.
	[I-D.ietf-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y.,		[I-D.ietf-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y.,
	"An extension to RELOAD to support Direct Response Routing", draft-		"An extension to RELOAD to support Direct Response Routing", draft-
	ietf-p2psip-drr-11 (work in progress), October 2013.		ietf-p2psip-drr-12 (work in progress), February 2014.
	12.2. Informative References		11.2. Informative References
	[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery		[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
	Using STUN", RFC5780, May 2010.		Using STUN", RFC5780, May 2010.
	[RFC3424] Daigle, L., "IAB Considerations for UNilateral Self-Address		[RFC3424] Daigle, L., "IAB Considerations for UNilateral Self-Address
	Fixing (UNSAF) Across Network Address Translation", RFC3424, November		Fixing (UNSAF) Across Network Address Translation", RFC3424, November
	2002.		2002.
	13. References
	Appendix A. Optional methods to investigate peer connectivity		Appendix A. Optional methods to investigate peer connectivity
	This section is for informational purposes only for providing some		This section is for informational purposes only for providing some
	mechanisms that can be used when the configuration information does		mechanisms that can be used when the configuration information does
	not specify if RPR can be used. It summarizes some methods which can		not specify if RPR can be used. It summarizes some methods which can
	be used for a peer to determine its own network location compared		be used for a peer to determine its own network location compared
	with NAT. These methods may help a peer to decide which routing mode		with NAT. These methods may help a peer to decide which routing mode
	it may wish to try. Note that there is no foolproof way to determine		it may wish to try. Note that there is no foolproof way to determine
	if a peer is publically reachable, other than via out-of-band		if a peer is publically reachable, other than via out-of-band
	mechanisms. This document addresses the UNSAF [RFC3424] concerns by		mechanisms. This document addresses the UNSAF [RFC3424] concerns by
	specifying a fallback plan to SRR [p2psip-base-draft]. SRR is not an		specifying a fallback plan to SRR [RFC6940]. SRR is not an UNSAF
	UNSAF mechanism. The document does not define any new UNSAF		mechanism. The document does not define any new UNSAF mechanisms.
	mechanisms.
	For RPR to function correctly, a peer may attempt to determine		For RPR to function correctly, a peer may attempt to determine
	whether it is publicly reachable. If it is not, RPR may be chosen to		whether it is publicly reachable. If it is not, RPR may be chosen to
	route the response with the help from relay peers, or the peers		route the response with the help from relay peers, or the peers
	should fall back to SRR. NATs and firewalls are two major		should fall back to SRR. NATs and firewalls are two major
	contributors preventing RPR from functioning properly. There are a		contributors preventing RPR from functioning properly. There are a
	number of techniques by which a peer can get its reflexive address on		number of techniques by which a peer can get its reflexive address on
	the public side of the NAT. After obtaining the reflexive address, a		the public side of the NAT. After obtaining the reflexive address, a
	peer can perform further tests to learn whether the reflexive address		peer can perform further tests to learn whether the reflexive address
	is publicly reachable. If the address appears to be publicly		is publicly reachable. If the address appears to be publicly
	skipping to change at page 14, line 5		skipping to change at page 12, line 13
	peers in the overlay. P2P routing algorithms can easily deliver a		peers in the overlay. P2P routing algorithms can easily deliver a
	request from a sending peer to a peer with whom the sending peer has		request from a sending peer to a peer with whom the sending peer has
	no direct connection. This makes it easy for a peer to ask other		no direct connection. This makes it easy for a peer to ask other
	peers to send unsolicited messages back to the requester.		peers to send unsolicited messages back to the requester.
	The approaches for a peer to get the addresses needed for the further		The approaches for a peer to get the addresses needed for the further
	tests, as well as the test for learning whether a peer may be		tests, as well as the test for learning whether a peer may be
	publicly reachable is same as the DRR case. Please refer to DRR		publicly reachable is same as the DRR case. Please refer to DRR
	document [I-D.ietf-p2psip-drr] for more details.		document [I-D.ietf-p2psip-drr] for more details.
			Appendix B. Comparison on cost of SRR and RPR
			The major advantage of the use of RPR is that it reduces the number
			of intermediate peers traversed by the response. By doing that, it
			reduces the load on those peers' resources like processing and
			communication bandwidth.
			B.1. Closed or managed networks
			As described in Section 3, many P2P systems run in a closed or
			managed environment (e.g., carrier networks) so that network
			administrators would know that they could safely use RPR.
			The number of hops for a response in SRR and RPR are listed in the
			following table. Note that the same illustrative settings can be
			found in DRR document [I-D.ietf-p2psip-drr].
			Mode | Success | No. of Hops | No. of Msgs
			----------------------------------------------------
			SRR | Yes | log(N) | log(N)
			RPR | Yes | 2 | 2
			RPR(DTLS) | Yes | 2 | 7+2
			Table 1. Comparison of SRR and RPR in closed networks
			From the above comparison, it is clear that:
			1) In most cases when the number of peers N > 4 (2^2), RPR uses fewer
			hops than SRR. Using a shorter route means less overhead and
			resource usage on intermediate peers, which is an important
			consideration for adopting RPR in the cases where the resources such
			as CPU and bandwidth are limited, e.g., the case of mobile, wireless
			networks.
			2) In the cases when N > 512 (2^9), RPR also uses fewer messages than
			SRR.
			3) In the cases when N < 512, RPR uses more messages than SRR (but
			still uses fewer hops than SRR). So the consideration on whether
			using RPR or SRR depends on other factors like using less resources
			(bandwidth and processing) from the intermediate peers. Section 4
			provides use cases where RPR has better chance to work or where the
			intermediary resources considerations are important.
			B.2. Open networks
			In open networks (e.g., Internet) where RPR is not guaranteed to
			work, RPR can fall back to SRR if it fails after trial, as described
			in Section 4. Based on the same settings of Section B.1, the number
			of hops, number of messages for a response in SRR and RPR are listed
			in the following table.
			Mode | Success | No. of Hops | No. of Msgs
			-----------------------------------------------------------
			SRR | Yes | log(N) | log(N)
			RPR | Yes | 2 | 2
			| Fail&Fall back to SRR | 2+log(N)| 2+log(N)
			RPR(DTLS) | Yes | 2 | 7+2
			| Fail&Fall back to SRR | 2+log(N)| 9+log(N)
			Table 2. Comparison of SRR and RPR in open networks
			From the above comparison, it can be observed that trying to first
			use RPR could still provide an overall number of hops lower than
			directly using SRR. The detailed analysis is same as DRR case and
			can be found in DRR document [I-D.ietf-p2psip-drr].
	Authors' Addresses		Authors' Addresses
	Ning Zong (editor)		Ning Zong
	Huawei Technologies		Huawei Technologies
	Email: zongning@huawei.com		Email: zongning@huawei.com
	Xingfeng Jiang		Xingfeng Jiang
	Huawei Technologies		Huawei Technologies
	Email: jiang.x.f@huawei.com		Email: jiang.x.f@huawei.com
	Roni Even		Roni Even
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