P2PSIP N. Zong Internet-Draft X. Jiang Intended status: Standards Track R. Even Expires: April 10, 2012 Huawei Technologies Y. Zhang China Mobile October 08, 2011 An extension to RELOAD to support Direct Response Routing draft-ietf-p2psip-drr-00 Abstract This document proposes an optional extension to RELOAD to support direct response routing mode. RELOAD recommends symmetric recursive routing for routing messages. The new optional extension provides a shorter route for responses reducing the overhead on intermediary peers and describes the potential cases where this extension can be used. 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 April 10, 2012. Copyright Notice Copyright (c) 2011 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 Zong, et al. Expires April 10, 2012 [Page 1] Internet-Draft P2PSIP DRR October 2011 to this document. 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Expires April 10, 2012 [Page 2] Internet-Draft P2PSIP DRR October 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Backgrounds . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1.1. Symmetric Recursive Routing (SRR) . . . . . . . . . . 5 3.1.2. Direct Response Routing (DRR) . . . . . . . . . . . . 6 3.2. Scenarios Where DRR can be Used . . . . . . . . . . . . . 7 3.2.1. Managed or Closed P2P System . . . . . . . . . . . . . 7 3.2.2. Wireless Scenarios . . . . . . . . . . . . . . . . . . 7 4. Relationship Between SRR and DRR . . . . . . . . . . . . . . . 8 4.1. How DRR Works . . . . . . . . . . . . . . . . . . . . . . 8 4.2. How SRR and DRR Work Together . . . . . . . . . . . . . . 8 5. Comparison on cost of SRR and DRR . . . . . . . . . . . . . . 8 5.1. Closed or managed networks . . . . . . . . . . . . . . . . 9 5.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 10 6. Extensions to RELOAD . . . . . . . . . . . . . . . . . . . . . 10 6.1. Basic Requirements . . . . . . . . . . . . . . . . . . . . 10 6.2. Modification To RELOAD Message Structure . . . . . . . . . 11 6.2.1. State-keeping Flag . . . . . . . . . . . . . . . . . . 11 6.2.2. Extensive Routing Mode . . . . . . . . . . . . . . . . 11 6.3. Creating a Request . . . . . . . . . . . . . . . . . . . . 12 6.3.1. Creating a Request for DRR . . . . . . . . . . . . . . 12 6.4. Request And Response Processing . . . . . . . . . . . . . 12 6.4.1. Destination Peer: Receiving a Request And Sending a Response . . . . . . . . . . . . . . . . . . . . . . 13 6.4.2. Sending Peer: Receiving a Response . . . . . . . . . . 13 7. Optional Methods to Investigate Node Connectivity . . . . . . 13 7.1. Getting Addresses To Be Used As Candidates for DRR . . . . 14 7.2. Public Reacheability Test . . . . . . . . . . . . . . . . 15 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 9.1. A new RELOAD Forwarding Option . . . . . . . . . . . . . . 16 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 11.1. Normative References . . . . . . . . . . . . . . . . . . . 16 11.2. Informative References . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Zong, et al. Expires April 10, 2012 [Page 3] Internet-Draft P2PSIP DRR October 2011 1. Introduction 1.1. Backgrounds RELOAD [I-D.ietf-p2psip-base] recommends symmetric recursive routing (SRR) for routing messages and describes the extensions that would be required to support additional routing algorithms. Other than SRR, two other routing options: direct response routing (DRR) and relay peer routing (RPR) are also discussed in Appendix D in [I-D.ietf- p2psip-base]. As we show in section 3, DRR is advantageous over SRR in some scenarios by reducing load (CPU and link BW) on intermediary peers . For example, in a closed network where every node is in the same address realm, DRR performs better than SRR. In other scenarios, using a combination of DRR and SRR together is more likely to bring benefits than if SRR is used alone. Some discussion on connectivity is in Non-Transitive Connectivity and DHTs [http://srhea.net/papers/ntr-worlds05.pdf]. Note that in this draft, we focus on DRR routing mode and its extensions to RELOAD to produce a standalone solution. Please refer to RPR draft [I-D.ietf-p2psip-rpr] for RPR routing mode. We first discuss the problem statement in Section 3, then how to combine DRR and SRR is presented in Section 4. In Section 5, we give comparison on the cost of SRR and DRR in both managed and open networks. An extension to RELOAD to support DRR is proposed in Section 6. Some optional methods to check node connectivity is introduced in Section 7, as informational text. 2. Terminology 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]. We use the terminology and definitions from the Concepts and Terminology for Peer to Peer SIP [I-D.ietf-p2psip-concepts] draft extensively in this document. We also use terms defined in NAT behavior discovery [I-D.ietf-behave-nat-behavior-discovery]. Other terms used in this document are defined inline when used and are also defined below for reference. There are two types of roles in the RELOAD architecture: peer and client. Node is used when describing both peer and client. In discussions specific to behavior of a peer or client, the term peer or client is used instead. Zong, et al. Expires April 10, 2012 [Page 4] Internet-Draft P2PSIP DRR October 2011 Publicly Reachable: A node is publicly reachable if it can receive unsolicited messages from any other node in the same overlay. Note: "publicly" does not mean that the nodes must be on the public Internet, because the RELOAD protocol may be used in a closed system. 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 following text. Symmetric Recursive Routing (SRR): refers to a routing mode in which responses follow the request path in the reverse order to get back to the sending peer. For simplicity, the abbreviation SRR is used instead in the following text. 3. Problem Statement RELOAD is expected to work under a great number of application scenarios. The situations where RELOAD is to be deployed differ greatly. For instance, some deployments are global, such as a Skype- like system intended to provide public service. Some run in closed networks of small scale. SRR works in any situation, but DRR may work better in some specific scenarios. 3.1. Overview RELOAD is a simple request-response protocol. After sending a request, a node waits for a response from a destination node. There are several ways for the destination node to send a response back to the source node. In this section, we will provide detailed information on two routing modes: SRR and DRR. Some assumptions are made in the following illustrations. 1) Peer A sends a request destined to a peer who is the responsible peer for Resource-ID k; 2) Peer X is the root peer being responsible for resource k; 3) The intermediate peers for the path from A to X are peer B, C, D. 3.1.1. Symmetric Recursive Routing (SRR) For SRR, when the request sent by peer A is received by an intermediate peer B, C or D, each intermediate peer will insert information on the peer from whom they got the request in the via- Zong, et al. Expires April 10, 2012 [Page 5] Internet-Draft P2PSIP DRR October 2011 list as described in RELOAD. As a result, the destination peer X will know the exact path which the request has traversed. Peer X will then send back the response in the reverse path by constructing a destination list based on the via-list in the request. A B C D X | Request | | | | |----------->| | | | | | Request | | | | |----------->| | | | | | Request | | | | |----------->| | | | | | Request | | | | |----------->| | | | | | | | | | Response | | | | |<-----------| | | | Response | | | | |<-----------| | | | Response | | | | |<-----------| | | | Response | | | | |<-----------| | | | | | | | | SRR works in any situation, especially when there are NATs or firewalls. A downside of this solution is that the message takes several hops to return to the client, increasing the bandwidth usage and CPU/battery load of multiple nodes. 3.1.2. Direct Response Routing (DRR) In DRR, peer X receives the request sent by peer A through intermediate peer B, C and D, as in SRR. However, peer X sends the response back directly to peer A based on peer A's local transport address. In this case, the response won't be routed through intermediate peers. Shorter route means less overhead on intermediary peers, especially in the case of wireless network where the CPU and uplink BW is limited. In the absence of NATs or other connectivity issues, this is the optimal routing technique. Note that establishing a secure connection requires multiple round trips. Please refer to Section 5 for cost comparison between SRR and DRR. Zong, et al. Expires April 10, 2012 [Page 6] Internet-Draft P2PSIP DRR October 2011 A B C D X | Request | | | | |----------->| | | | | | Request | | | | |----------->| | | | | | Request | | | | |----------->| | | | | | Request | | | | |----------->| | | | | | | | | | Response | |<-----------+------------+------------+------------| | | | | | 3.2. Scenarios Where DRR can be Used This section lists several scenarios where using DRR would work, and when the increased efficiency would be advantageous. 3.2.1. Managed or Closed P2P System The properties that make P2P technology attractive, such as the lack of need for centralized severs, self-organization, etc. are attractive for managed systems as well as unmanaged systems. Many of these systems are deployed on private network where nodes are in the same address realm and/or can directly route to each other. In such a scenario, the network administrator can indicate preference for DRR in the peer's configuration file. Peers in such a system would always try DRR first, but peers must also support SRR in case DRR fails. If during the process of establishing a direct connection with the sending peer, the responding peer receives a response with SRR as the preferred routing mode (or it fails to establish the direct connection), the responding peer should not use DRR but switch to SRR. A node can keep a list of unreachable nodes based on trying DRR and use only SRR for these nodes. The advantage in using DRR is on the network stability since it puts less overhead on the intermediary peers that will not route the responses. The intermediary peers will need to route less messages and save CPU resources as well as the link bandwidth usage. 3.2.2. Wireless Scenarios While some mobile deployments may use clients, in mobile networks with full peers, there is an advantage to using DRR in order to reduce the load on intermediary nodes. Using DRR helps with reducing radio battery usage and bandwidth by the intermediary peers. The service provider may recommend in the configuration using DRR based on his knowledge of the topology. Zong, et al. Expires April 10, 2012 [Page 7] Internet-Draft P2PSIP DRR October 2011 4. Relationship Between SRR and DRR 4.1. How DRR Works DRR is very simple. The only requirement is for the source peers to provide their (publically reachable) transport address to the destination peers, so that the destination peer knows where to send the response. Responses are sent directly to the requesting peer. 4.2. How SRR and DRR Work Together DRR is not intended to replace SRR. As seen from Section 3, DRR has better performance in some scenarios, but have limitations as well, see for example section 4.3 in Non-Transitive Connectivity and DHTs [http://srhea.net/papers/ntr-worlds05.pdf]. As a result, it is better to use these two modes together to adapt to each peer's specific situation. In this section, we give some informative suggestions on how to transition between the routing modes in RELOAD. A peer can collect statistical data on the success of the different routing modes based on previous transactions and keep a list of non- reachable addresses. Based on the data, the peer will have a clearer view about the success rate of different routing modes. Other than the success rate, the peer can also get data of fine granularity, for example, the number of retransmission the peer needs to achieve a desirable success rate. A typical strategy for the node is as follows. A node chooses to start with DRR. Based on the success rate as seen from the lost message statistics or responses that used DRR, the node can either continue to offer DRR first or switch to SRR. The node can decide whether to try DRR based on other information such as configuration file information. If an overlay runs within a private network and all nodes in the system can reach each other directly, nodes may send most of the transactions with DRR. 5. Comparison on cost of SRR and DRR The major advantages in using DRR are in going through less intermediary peers on the response. By doing that it reduces the load on those peers' resources like processing and communication bandwidth. Zong, et al. Expires April 10, 2012 [Page 8] Internet-Draft P2PSIP DRR October 2011 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 DRR. SRR brings out more routing hops than DRR. Assuming that there are N nodes in the P2P system and Chord is applied for routing, the number of hops for a response in SRR and DRR are listed in the following table. Establishing a secure connection between sending peer and responding peer with (D)TLS requires multiple messages. Note that establishing (D)TLS secure connections for P2P overlay is not optimal in some cases, e.g. direct response routing where (D)TLS is heavy for temporary connections. Instead, some alternate security techniques, e.g. using public keys of the destination to encrypt the messages, signing timestamps to prevent reply attacks can be adopted. Therefore, in the following table, we show the cases of: 1) no (D)TLS in DRR; 2) still using DTLS in DRR as sub-optimal and, as the worst- cost case, 7 messages are used during the DTLS handshaking [DTLS]. (TLS Handshake is two round-trip negotiation protocol while DTLS handshake is three round-trip negotiation protocol.) Mode | Success | No. of Hops | No. of Msgs ---------------------------------------------------- SRR | Yes | logN | logN DRR | Yes | 1 | 1 DRR(DTLS) | Yes | 1 | 7+1 From the above comparison, it is clear that: 1) In most cases of N > 2 (2^1), DRR has fewer hops than SRR. Shorter route means less overhead and resource usage on intermediary peers, which is an important consideration for adopting DRR in the cases where the resource such as CPU and BW is limited, e.g. the case of mobile, wireless network. 2) In the cases of N > 256 (2^8), DRR also has fewer messages than SRR. 3) In the cases where N < 256, DRR has more messages than SRR (but still has fewer hops than SRR). So the consideration to use DRR or SRR depends on other factors like using less resources (bandwidth and processing) from the intermediaries peers. Section 4 provides use cases where DRR has better chance to work or where the intermediary resources considerations are important. Zong, et al. Expires April 10, 2012 [Page 9] Internet-Draft P2PSIP DRR October 2011 5.2. Open networks In open network where DRR is not guaranteed, DRR can fall back to SRR If it fails after trial, as described in Section 4. Based on the same settings in Section 5.1, the number of hops, number of messages for a response in SRR and DRR are listed in the following table. Mode | Success | No. of Hops | No. of Msgs ----------------------------------------------------------- SRR | Yes | logN | logN DRR | Yes | 1 | 1 | Fail&Fall back to SRR | 1+logN | 1+logN DRR(DTLS) | Yes | 1 | 7+1 | Fail&Fall back to SRR | 1+logN | 8+logN From the above comparison, it can be observed that: 1) Trying DRR would still have a good chance of fewer hops than SRR. Suppose that P peers are publicly reachable, the number of hops in DRR and SRR is P*1+(N-P)*(1+logN), N*logN, respectively. The condition for fewer hops in DRR is P*1+(N-P)*(1+logN) < N*logN, which is P/N > 1/logN. This means that when the number of peers N grows, the required ratio of publicly reachable peers P/N for fewer hops in DRR decreases. Therefore, the chance of trying DRR with fewer hops than SRR becomes better as the scale of the network increases. 2) In the cases of large network and the success rate of DRR is good, it is still possible that DRR has fewer messages than SRR. Otherwise, the consideration to use DRR or SRR depends on other factors like using less resources from the intermediaries peers. 6. Extensions to RELOAD Adding support for DRR requires extensions to the current RELOAD protocol. In this section, we define the changes required to the protocol, including changes to message structure and to message processing. 6.1. Basic Requirements All peers implementing DRR MUST support SRR. All peers MUST be able to process requests for routing in SRR, and MAY support DRR routing requests. Zong, et al. Expires April 10, 2012 [Page 10] Internet-Draft P2PSIP DRR October 2011 6.2. Modification To RELOAD Message Structure RELOAD provides an extensible framework to accommodate future extensions. In this section, we define a ForwardingOption structure to support DRR mode. Additionally we present a state- keeping flag to inform intermediate peers if they are allowed to not maintain state for a transaction. 6.2.1. State-keeping Flag RELOAD allows intermediate peers to maintain state in order to implement SRR, for example for implementing hop-by-hop retransmission. If DRR is used, the response will not follow the reverse path, and the state in the intermediate peers won't be cleared until such state expires. In order to address this issue, we propose a new flag, state-keeping flag, in the message header to indicate whether the state keeping is not required in the intermediate peers. flag : 0x8 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 This draft introduces a new forwarding option for an extensive routing mode. This option conforms to the description in section 5.3.2.3 in [I-D.ietf-p2psip-base]. We first define a new type to define the new option, EXTENSIVE_ROUTING_MODE_TYPE: The option value will be illustrated in the following figure, defining the ExtensiveRoutingModeOption structure: enum { 0x0, 0x01 (DRR), 0x02(RPR), 255} RouteMode; struct { RouteMode routemode; OverlayLink transport; IpAddressPort ipaddressport; Destination destination<1..2^8-1>; } ExtensiveRoutingModeOption; The above structure reuses: Transport, Destination and IpAddressPort structure defined in section 5.3.1.1 and 5.3.2.2 in [I-D.ietf-p2psip- Zong, et al. Expires April 10, 2012 [Page 11] Internet-Draft P2PSIP DRR October 2011 base]. Route mode: refers to which type of routing mode is indicated to the destination peer. Currently, only DRR and RPR (specified in RPR draft [I-D.ietf-p2psip-rpr]) are defined. Transport: refers to the transport type which is used to deliver responses from the destination peer to the sending peer. IpAddressPort: refers to the transport address that the destination peer should use to send the response to. This will be a sending node address for DRR. Destination: refers to the sending node itself. If the routing mode is DRR, then the destination only contains the sending node's node-id. 6.3. Creating a Request 6.3.1. Creating a Request for DRR When using DRR for a transaction, the sending peer MUST set the IGNORE-STATE-KEEPING flag in the ForwardingHeader. Additionally, the peer MUST construct and include a ForwardingOptions structure in the ForwardingHeader. When constructing the ForwardingOption structure, the fields MUST be set as follows: 1) The type MUST be set to EXTENSIVE_ROUTING_MODE_TYPE. 2) The ExtensiveRoutingModeOption structure MUST be used for the option field within the ForwardingOptions structure. The fields MUST be defined as follows: 2.1) RouteMode set to 0x01 (DRR). 2.2) Transport set as appropriate for the sender. 2.3) IPAddressPort set to the peer's associated transport address. 2.4) The destination structure MUST contain one value, defined as type peer and set with the sending peer's own values. 6.4. Request And Response Processing This section gives normative text for message processing after DRR is introduced. Here, we only describe the additional procedures for supporting DRR. Please refer to [I-D.ietf-p2psip-base] for RELOAD base procedures. Zong, et al. Expires April 10, 2012 [Page 12] Internet-Draft P2PSIP DRR October 2011 6.4.1. Destination Peer: Receiving a Request And Sending a Response When the destination peer receives a request, it will check the options in the forwarding header. If the destination peer can not understand extensive_routing_mode option in the request, it MUST attempt to use SRR to return an "Error_Unknown_Extension" response (defined in Section 5.3.3.1 and Section 13.9 in [I-D.ietf-p2psip- base]) to the sending peer. If the routing mode is DRR, the peer MUST construct the Destination list for the response with only one entry, using the sending peer's node-id from the option in the request as the value. In the event that the routing mode is set to DRR and there is not exactly one destination, the destination peer MUST try to return an "Error_Unknown_Extension" response (defined in Section 5.3.3.1 and Section 13.9 in [I-D.ietf-p2psip-base]) to the sending peer using SRR. After the peer constructs the destination list for the response, it sends the response to the transport address which is indicated in the IpAddressPort field in the option using the specific transport mode in the Forwardingoption. If the destination peer receives a retransmit with SRR preference on the message it is trying to response to now, the responding peer should abort the DRR response and use SRR. 6.4.2. Sending Peer: Receiving a Response Upon receiving a response, the peer follows the rules in [I-D.ietf- p2psip-base]. The peer should note if DRR worked in order to decide if to offer DRR again. If the peer does not receive a response until the timeout it SHOULD resend the request using SRR. 7. Optional Methods to Investigate Node Connectivity This section is for informational purposes only for providing some mechanisms that can be used when the configuration information does not specify if DRR can be used. It summarizes some methods which can be used for a node to determine its own network location compared with NAT. These methods may help a node to decide which routing mode it may wish to try. Note that there is no foolproof way to determine if a node is publically reachable, other than via out-of-band mechanisms. As such, peers using these mechanisms may be able to optimize traffic, but must be able to fall back to SRR routing if the other routing mechanisms fail. Zong, et al. Expires April 10, 2012 [Page 13] Internet-Draft P2PSIP DRR October 2011 For DRR to function correctly, a node may attempt to determine whether it is publicly reachable. If it is not, the peers should fall back to SRR. If the peer believes it is publically reachable, DRR may be attempted. NATs and firewalls are two major contributors preventing DRR from functioning properly. There are a number of techniques by which a node can get its reflexive address on the public side of the NAT. After obtaining the reflexive address, a peer can perform further tests to learn whether the reflexive address is publicly reachable. If the address appears to be publicly reachable, the nodes to which the address belongs can use DRR for responses. Some conditions are unique in P2PSIP architecture which could be leveraged to facilitate the tests. In P2P overlay network, each node only has partial a view of the whole network, and knows of a few nodes in the overlay. P2P routing algorithms can easily deliver a request from a sending node to a peer with whom the sending node has no direct connection. This makes it easy for a node to ask other nodes to send unsolicited messages back to the requester. In the following sections, we first introduce several ways for a node to get the addresses needed for the further tests. Then a test for learning whether a peer may be publicly reachable is proposed. 7.1. Getting Addresses To Be Used As Candidates for DRR In order to test whether a peer may be publicly reachable, the node should first get one or more addresses which will be used by other nodes to send him messages directly. This address is either a local address of a node or a translated address which is assigned by a NAT to the node. STUN is used to get a reflexive address on the public side of a NAT with the help of STUN servers. There is also a STUN usage [I-D.ietf- behave-nat-behavior-discovery] to discover NAT behavior. Under RELOAD architecture, a few infrastructure servers can be leveraged for this usage, such as enrollment servers, diagnostic servers, bootstrap servers, etc. The node can use a STUN Binding request to one of STUN servers to trigger a STUN Binding response which returns the reflexive address from the server's perspective. If the reflexive transport address is the same as the source address of the Binding request, the node can determine that there likely is no NAT between him and the chosen infrastructure server. (Certainly, in some rare cases, the allocated address happens to be the same as the source address. Further tests will detect this case and rule it out in the end.). Usually, these infrastructure severs are publicly reachable in the overlay, so the Zong, et al. Expires April 10, 2012 [Page 14] Internet-Draft P2PSIP DRR October 2011 node can be considered publicly reachable. On the other hand, with the techniques in [I-D.ietf-behave-nat-behavior-discovery], a node can also decide whether it is behind NAT with endpoint-independent mapping behavior. If the node is behind a NAT with endpoint- independent mapping behavior, the reflexive address should also be a candidate for further tests. UPnP-IGD is a mechanism that a node can use to get the assigned address from its residential gateway and after obtaining this address to communicate it with other nodes, the node can receive unsolicited messages from outside, even though it is behind a NAT. So the address obtained through the UPnP mechanism should also be used for further tests. Another way that a node behind NAT can use to learn its assigned address by NAT is NAT-PMP. Like in UPnP-IGD, the address obtained using this mechanism should also be tested further. The above techniques are not exhaustive. These techniques can be used to get candidate transport addresses for further tests. 7.2. Public Reacheability Test Using the transport addresses obtained by the above techniques, a node can start a test to learn whether the candidate transport address is publicly reachable. The basic idea for the test is for a node to send a request and expect another node in the overlay to send back a response. If the response is received by the sending node successfully and also the node giving the response has no direct connection with the sending node, the sending node can determine that the address is probably publicly reachable and hence the node may be publicly reachable at the tested transport address. In P2P overlay, a request is routed through the overlay and finally a destination peer will terminate the request and give the response. In a large system, there is a high probability that the destination peer has no direct connection with the sending node. Especially in RELOAD architecture, every node maintains a connection table. So it is easier for a node to check whether it has direct connection with another node. Note: Currently, no existing message in base RELOAD can achieve the test. In our opinion, this kind of test is within diagnostic scope, so authors hope WG can define a new diagnostic message to do that. We don't plan to define the message in this document, for the objective of this draft is to propose an extension to support DRR. The following text is informative. Zong, et al. Expires April 10, 2012 [Page 15] Internet-Draft P2PSIP DRR October 2011 If a node wants to test whether its transport address is publicly reachable, it can send a request to the overlay. The routing for the test message would be different from other kinds of requests because it is not for storing/fetching something to/from the overlay or locating a specific node, instead it is to get a peer who can deliver the sending node an unsolicited response and which has no direct connection with him. Each intermediate peer receiving the request first checks whether it has a direct connections with the sending peer. If there is a direct connection, the request is routed to the next peer. If there is no direct connection, the intermediate peer terminates the request and sends the response back directly to the sending node with the transport address under test. After performing the test, if the peer determines that it may be publicly reachable, it can try DRR in subsequent transaction. 8. Security Considerations TBD 9. IANA Considerations 9.1. A new RELOAD Forwarding Option A new RELOAD Forwarding Option type is add to the Registry. Type: 0x2 - extensive_routing_mode 10. Acknowledgements David Bryan has helped extensively with this document, and helped provide some of the text, analysis, and ideas contained here. The authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti Lakshminath, Bruce Lowekamp and Stephane Bryant for their constructive comments. 11. References 11.1. Normative References [I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) Base Protocol", draft-ietf-p2psip-base-18 (work in progress), August 2011. Zong, et al. Expires April 10, 2012 [Page 16] Internet-Draft P2PSIP DRR October 2011 [I-D.ietf-p2psip-concepts] Bryan, D., Matthews, P., Shim, E., Willis, D., and S. Dawkins, "Concepts and Terminology for Peer to Peer SIP", draft-ietf-p2psip-concepts-03 (work in progress), October 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 11.2. Informative References [ChurnDHT] Rhea, S., "Handling Churn in a DHT", Proceedings of the USENIX Annual Technical Conference. Handling Churn in a DHT, June 2004. [DTLS] Modadugu, N., Rescorla, E., "The Design and Implementation of Datagram TLS", 11th Network and Distributed System Security Symposium (NDSS), 2004. [I-D.ietf-behave-nat-behavior-discovery] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery Using STUN", draft-ietf-behave-nat-behavior-discovery-04 (work in progress), July 2008. [I-D.ietf-behave-tcp] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, "NAT Behavioral Requirements for TCP", draft-ietf-behave-tcp-08 (work in progress), September 2008. [I-D.lowekamp-mmusic-ice-tcp-framework] Lowekamp, B. and A. Roach, "A Proposal to Define Interactive Connectivity Establishment for the Transport Control Protocol (ICE-TCP) as an Extensible Framework", draft-lowekamp-mmusic-ice-tcp-framework-00 (work in progress), October 2008. [RFC4787] Audet, F. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, January 2007. [I-D.ietf-p2psip-rpr] Zong, N., Jiang, X., Even, R. and Zhang, Y., "An extension to RELOAD to support Relay Peer Routing", draft-ietf-p2psip-rpr-00, October 2011. Authors' Addresses Ning Zong Huawei Technologies Email: zongning@huawei.com Zong, et al. Expires April 10, 2012 [Page 17] Internet-Draft P2PSIP DRR October 2011 Xingfeng Jiang Huawei Technologies Email: jiang.x.f@huawei.com Roni Even Huawei Technologies Email: even.roni@huawei.com Yunfei Zhang China Mobile Email: zhangyunfei@chinamobile.com Zong, et al. Expires April 10, 2012 [Page 18]