wdiff rfc7263.alt-original rfc7263.txt

P2PSIP
Internet Engineering Task Force (IETF) N. Zong, Ed.
Internet-Draft Zong
Request for Comments: 7263 X. Jiang
Intended status:
Category: Standards Track R. Even
Expires: April 24, 2014
ISSN: 2070-1721 Huawei Technologies
Y. Zhang
CoolPad
October 21, 2013 / China Mobile
June 2014

An Extension to the REsource LOcation And Discovery (RELOAD) Protocol
to Support Direct Response Routing
draft-ietf-p2psip-drr-11

Abstract

This document proposes defines an optional extension to the REsource LOcation
And Discovery (RELOAD) protocol to support the direct response
routing mode. RELOAD recommends symmetric recursive routing for
routing messages. The new optional extension provides a shorter
route for responses responses, thereby reducing the overhead on intermediate peers and peers.
This document also 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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
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material or to cite them other than as "work in progress."

This Internet-Draft will expire on April 24, 2014.
http://www.rfc-editor.org/info/rfc7263.

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Provisions Relating to IETF Documents
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 ....................................................4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 .....................................................4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ........................................................5
3.1. SRR and DRR . . . . . . . . . . . . . . . . . . . . . . . 4 ................................................5
3.1.1. Symmetric Recursive Routing (SRR) . . . . . . . . . . 4 ...................6
3.1.2. Direct Response Routing (DRR) . . . . . . . . . . . . 5 .......................6
3.2. Scenarios where Where DRR can be used . . . . . . . . . . . . . 6 Can Be Used ............................7
3.2.1. Managed or closed Closed P2P systems . . . . . . . . . . . . 6 Systems .......................7
3.2.2. Wireless scenarios . . . . . . . . . . . . . . . . . 6 Scenarios ..................................8
4. Relationship between SRR and DRR . . . . . . . . . . . . . . 6 ................................8
4.1. How DRR works . . . . . . . . . . . . . . . . . . . . . . 7 Works ..............................................8
4.2. How SRR and DRR work together . . . . . . . . . . . . . . 7 Work Together ..............................8
5. DRR extensions Extensions to RELOAD . . . . . . . . . . . . . . . . . . 9 ........................................9
5.1. Basic requirements . . . . . . . . . . . . . . . . . . . 9 Requirements .........................................9
5.2. Modification to RELOAD message structure . . . . . . . . 10 Message Structure ...................9
5.2.1. State-keeping flag . . . . . . . . . . . . . . . . . 10 State-Keeping Flag ..................................9
5.2.2. Extensive routing mode . . . . . . . . . . . . . . . 10 Routing Mode .............................10
5.3. Creating a request . . . . . . . . . . . . . . . . . . . 11 Request ........................................11
5.3.1. Creating a request Request for DRR . . . . . . . . . . . . . 11 .........................11
5.4. Request and response processing . . . . . . . . . . . . . 12 Response Processing ...........................11
5.4.1. Destination peer: receiving Peer: Receiving a request Request and sending
Sending a
response . . . . . . . . . . . . . . . . . . . . . . 12 Response .................................11
5.4.2. Sending peer: receiving Peer: Receiving a response . . . . . . . . . 12 Response .................12
6. Overlay configuration extension . . . . . . . . . . . . . . . 12 Configuration Extension ................................12
7. Security considerations . . . . . . . . . . . . . . . . . . . 13 Considerations ........................................12
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 13 Considerations ............................................13
8.1. A new New RELOAD forwarding option . . . . . . . . . . . . . 13 Forwarding Option ............................13
8.2. A new New IETF XML registry . . . . . . . . . . . . . . . . . 13 Registry ...................................13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 ................................................13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 ....................................................13
10.1. Normative references . . . . . . . . . . . . . . . . . . 14 References .....................................13
10.2. Informative references . . . . . . . . . . . . . . . . . 14 References ...................................14
Appendix A. Optional methods Methods to investigate peer connectivity . 14 Investigate Peer Connectivity .....15
A.1. Getting addresses Addresses to be used Be Used as candidates Candidates for DRR . . . 15 .........15
A.2. Public reachability test . . . . . . . . . . . . . . . . 16 Reachability Test ...................................16
Appendix B. Comparison on cost of Cost of SRR and DRR . . . . . . . . . 15 .....................17
B.1. Closed or managed networks . . . . . . . . . . . . . . . 15 Managed Networks .................................17
B.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Networks ..............................................19

1. Introduction

The REsource LOcation And Discovery (RELOAD) protocol [I-D.ietf-p2psip-
base] [RFC6940]
recommends symmetric recursive routing (SRR) for routing messages and
describes the extensions that would be required to support additional
routing algorithms. Other than In addition to SRR, two other routing options: options --
direct response routing (DRR) and relay peer routing (RPR) -- are
also discussed in Appendix A of [I-D.ietf-p2psip-base]. [RFC6940]. As we show in section Section 3,
DRR is advantageous over SRR in some scenarios
by reducing in that DRR can reduce
load (CPU and link bandwidth) on intermediate peers. For example, in
a closed network where every peer 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 provide benefits than if SRR
is used alone.

Note that in this document, document we focus on the DRR routing mode and its
extensions to RELOAD to produce a standalone solution. Please refer
to RPR draft [I-D.ietf-p2psip-rpr] [RFC7264] for details on the RPR routing mode.

We first discuss the problem statement in Section 3, then how 3. 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 defined in Section 6. 5. Some optional methods to check
peer connectivity are introduced in Appendix A. In Appendix B, we
give a comparison of the cost of SRR and DRR in both managed and open
networks.

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 RELOAD base draft
[I-D.ietf-p2psip-base] RELOAD specification
[RFC6940] extensively in this document. We also use terms defined in
the NAT behavior discovery document [RFC5780]. Other terms used in
this document are defined inline when used and are also defined below
for reference.

Publicly Reachable: A peer is publicly reachable if it can receive
unsolicited messages from any other peer in the same overlay.
Note: "publicly" "Publicly" does not mean that the peers must be on the
public Internet, because the RELOAD protocol may be used in a
closed network.

Direct Response Routing (DRR): "DRR" refers to a routing mode in
which responses to P2PSIP Peer-to-Peer SIP (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 "DRR" is used instead in the rest of the this
document.

Symmetric Recursive Routing (SRR): "SRR" refers to a routing mode
in which responses follow the reverse path of the request to get
to the sending peer. For simplicity, the abbreviation SRR "SRR" is
used
instead in the rest of this document.

Relay Peer Routing (RPR): "RPR" refers to a routing mode in which
responses to P2PSIP requests are sent by the destination peer to
the transport address of a relay peer that will forward the
responses towards the sending peer. For simplicity, the
abbreviation "RPR" is used in the rest of this document.

3. Overview

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
Skype-like system intended to provide public service, while others
run in small-scale closed networks of small scale. networks. SRR works in any situation, but
DRR may work better in some specific scenarios.

3.1. SRR and DRR

RELOAD is a simple request-response protocol. After sending a
request, a peer waits for a response from a destination peer. There
are several ways for the destination peer to send a response back to
the source peer. In this section, we will provide detailed
information on two routing modes: SRR and DRR.

Some assumptions are made in the following illustrations. illustrations that follow:

1) Peer A sends a request destined to a peer who is the responsible
peer for a Resource-ID k; k.

2) Peer X is the root peer being responsible for resource k; Resource-ID k.

3) The intermediate peers for the path from A to X are peer peers B, C,
and 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 C, or D, each intermediate peer will insert
information on the peer from whom they got the request in the via-
list
Via List, as described in RELOAD. RELOAD [RFC6940]. As a result, the
destination peer X will know the exact path which that the request has
traversed. Peer X will then send back the response in the reverse
path by constructing a destination list Destination List based on the via-list Via List in the
request. Figure 1 illustrates SRR.

A B C D X
| Request | | | |
|----------->| | | |
| | Request | | |
| |----------->| | |
| | | Request | |
| | |----------->| |
| | | | Request |
| | | |----------->|
| | | | |
| | | | Response |
| | | |<-----------|
| | | Response | |
| | |<-----------| |
| | Response | | |
| |<-----------| | |
| Response | | | |
|<-----------| | | |
| | | | |

Figure 1. 1: SRR routing mode Mode

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 peer, increasing the bandwidth usage
and CPU/battery load of multiple peers.

3.1.2. Direct Response Routing (DRR)

In DRR, peer X receives the request sent by peer A through
intermediate peer peers B, C 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 is not routed through
intermediate peers. Figure 2 illustrates DRR. Using a shorter route
means less overhead on intermediate peers, especially in the case of
wireless networks where the CPU and uplink bandwidth is are limited.
For example, in the absence of NATs, or if the NAT implements endpoint-
independent
endpoint-independent filtering, this is the optimal routing
technique. Note that establishing a secure connection requires
multiple round trips. Please refer to Section 5 Appendix B for a cost
comparison between SRR and DRR.

A B C D X
| Request | | | |
|----------->| | | |
| | Request | | |
| |----------->| | |
| | | Request | |
| | |----------->| |
| | | | Request |
| | | |----------->|
| | | | |
| | | | Response |
|<-----------+------------+------------+------------|
| | | | |

Figure 2. 2: DRR routing mode Mode

3.2. Scenarios where Where DRR can be used Can Be Used

This section lists several scenarios where using DRR would work, work and
identifies when the increased efficiency would be advantageous.

3.2.1. Managed or closed Closed P2P systems Systems

The properties that make P2P technology attractive, such as the lack
of need for centralized servers, self-organization, etc. etc., are
attractive for managed systems as well as unmanaged systems. Many of
these systems are deployed on private networks where peers 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 During the process of establishing a direct connection with
the sending peer, if the responding peer receives a request with SRR
as the preferred routing mode (or it fails to establish the direct
connection), the responding peer SHOULD NOT use DRR but instead
switch to SRR. The simple policy is to try DRR and and, if fails this fails,
switch to SRR for all connections. A finer grained policy is when In a finer-grained policy, a peer keeps
would keep a list of unreachable peers based on trying DRR and then
would use only SRR for
these those peers. The advantage in of using DRR is on the
network stability stability, since it puts less overhead on the intermediate
peers that will not route the responses. The intermediate peers will
need to route less fewer messages and will save CPU resources as well as the
link bandwidth usage.

3.2.2. Wireless scenarios Scenarios

In some mobile deployments, using DRR may help with reducing reduce radio battery
usage and bandwidth by the intermediate peers. The service provider
may recommend using DRR based on his/her his knowledge of the topology.

4. Relationship between SRR and DRR

4.1. How DRR works Works

DRR is very simple. The only requirement is for the source peers to
provide their potential (publically (publicly 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 Work Together

DRR is not intended to replace SRR. 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 for how to transition
between the routing modes in RELOAD.

According to base draft [I-D.ietf-p2psip-base], [RFC6940], SRR MUST be supported. An overlay MAY be
configured to use alternative routing algorithms, and alternative
routing algorithms MAY be selected on a per-message basis. I.e., That is,
a node in an overlay which that supports SRR and some other routing algorithm,
algorithm -- for example DRR, example, DRR -- might use SRR some of the time and
DRR some of the time. A node joining the overlay should get from the configuration file the
preferred routing mode. mode from the configuration file. If an overlay
runs within a private network and all peers in the system can reach
each other directly, peers MAY send most of the transactions with
DRR. On the contrary, using However, DRR SHOULD NOT be discouraged used in the open Internet or if the
administrator does not feel he have has enough information about the
overlay network topology. A new overlay configuration element
specifying the usage of DRR is defined in Section 7. 6.

Alternatively, 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 this data, the peer will
have a clearer view about of the success rate of different routing modes. Other than
In addition to data on the success rate, the peer can also get data
of finer granularity, granularity -- for example, the number of retransmission retransmissions
the peer needs to achieve a desirable success rate.

A typical strategy for the peer is as follows. A peer chooses to
start with DRR based on the configuration. Based on the success rate
seen from the lost message
as indicated by statistics on lost messages or by responses that used
DRR, the peer can either continue to offer DRR first or switch to
SRR. Note that a peer should use the DRR success statistic statistics to
decide if whether to continue using DRR or fall back to SRR. It is not recommended to
make Making
such a decision per specific connection but this is not recommended; this
should be an application decision.

5. DRR extensions Extensions to RELOAD

Adding support for DRR requires extensions to the current RELOAD
protocol. In this section, we define the extensions required to the
protocol, extensions,
including extensions to message structure and to message processing.

5.1. Basic requirements Requirements

All peers MUST be able to process requests for routing in SRR, SRR and MAY
support DRR routing requests.

5.2. Modification to RELOAD message structure Message Structure

RELOAD provides an extensible framework to accommodate future
extensions. In this section, we define a ForwardingOption structure
to support DRR mode. Additionally Additionally, we present a state-keeping flag
to inform intermediate peers if they are allowed to not maintain
state for a transaction.

5.2.1. State-keeping flag State-Keeping Flag

RELOAD allows intermediate peers to maintain state in order to
implement SRR, SRR -- for example 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 will not be
cleared until such state expires. In order to address this issue, we
propose
define a new flag, state-keeping flag, in the message header ForwardingOption
structure to indicate whether the state keeping state-keeping is required in the
intermediate peers.

flag :

Flag: 0x08 IGNORE-STATE-KEEPING

If IGNORE-STATE-KEEPING is set, any peer receiving this message and
which but
who is not the destination of the message SHOULD forward the message
with the full via_list Via List and SHOULD NOT maintain any internal state.

5.2.2. Extensive routing mode Routing Mode

This draft document introduces a new forwarding option for an extensive
routing mode. This option conforms to the description in section
Section 6.3.2.3 of [I-D.ietf-p2psip-base]. [RFC6940].

We first define a new type to define the new option,
extensive_routing_mode:

The option value is illustrated as below, defining that defines the ExtensiveRoutingModeOption structure:
structure is illustrated below:

enum {(0),DRR(1),(255)} RouteMode;
struct {
RouteMode routemode;
OverlayLinkType transport;
IpAddressPort ipaddressport;
Destination destinations<1..2^8-1>;
} ExtensiveRoutingModeOption;

The above structure reuses the OverlayLinkType, Destination Destination, and
IpAddressPort structure structures as defined in section Sections 6.5.1.1, 6.3.2.2 6.3.2.2, and
6.3.1.1 of [I-D.ietf-p2psip-base]. [RFC6940], respectively.

RouteMode: refers to which type of routing mode is indicated to the
destination peer.

OverlayLinkType: refers to the transport type which that is used to deliver
responses from the destination peer to the sending peer.

IpAddressPort: refers to the transport address that the destination
peer will use to send the response to. for sending responses. This will be a sending peer
address for DRR.

Destination: refers to the sending peer itself. If the routing mode
is DRR, then the destination only contains the sending peer's Node-
ID.
Node-ID.

5.3. Creating a request Request

5.3.1. Creating a request 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 ForwardingOption 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.

2) The ExtensiveRoutingModeOption structure MUST be used for the
option field within the ForwardingOptions ForwardingOption 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 node "node" and set with the sending peer's own values.

5.4. Request and response processing 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] [RFC6940] for RELOAD base
procedures.

5.4.1. Destination peer: receiving Peer: Receiving a request Request and sending Sending a response Response

When the destination peer receives a request, it will check the
options in the forwarding header. If the destination peer can not cannot
understand the extensive_routing_mode option in the request, it MUST
attempt to use SRR to return an "Error_Unknown_Extension" response
(defined in Section Sections 6.3.3.1 and Section 14.9 of [I-D.ietf-p2psip-
base]) [RFC6940]) to the sending
peer.

If the routing mode is DRR, the destination peer MUST construct the
Destination
list List for the response with only one entry, using the sending
requesting peer's Node-ID from the option Via List 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 Sections 6.3.3.1 and
Section
14.9 of [I-D.ietf-p2psip-base]) [RFC6940]) to the sending peer using SRR.

After the peer constructs the destination list Destination List for the response, it
sends the response to the transport address address, which is indicated in
the ipaddressport field in the option using the specific transport
mode in the Forwardingoption. ForwardingOption. If the destination peer receives a
retransmit with SRR preference on the message it is trying to respond
to now, the responding peer SHOULD abort the DRR response and
use SRR.

5.4.2. Sending peer: receiving Peer: Receiving a response Response

Upon receiving a response, the peer follows the rules in [I-D.ietf-
p2psip-base]. [RFC6940].
The peer SHOULD note if DRR worked worked, in order to decide
if whether to
offer DRR again. If the peer does not receive a response until the timeout
timeout, it SHOULD resend the request using SRR.

6. Overlay configuration extension Configuration Extension

This document extends the RELOAD overlay configuration (see
Section 11.1 of [I-D.ietf-p2psip-base]) [RFC6940]) by adding one new element, "route-mode",
inside each "configuration" element.

The Compact Relax NG Grammar Regular Language for XML Next Generation (RELAX NG)
grammar for this element is:

namespace route-mode = "urn:ietf:params:xml:ns:p2p:route-mode"

parameter &= element route-mode:mode { xsd:string }?

This namespace is added into the <mandatory-extension> element in the
overlay configuration file. The defined routing modes include DRR
and RPR.

Mode

The mode can be DRR or RPR and and, if specified in the configuration configuration,
should be the preferred routing mode used by the application.

7. Security considerations Considerations

The normative security recommendations of Section 13 of base draft
[I-D.ietf-p2psip-base] [RFC6940] are
applicable to this document. As a routing alternative, the security
part of DRR conforms to Section 13.6 of the
base draft [RFC6940], which describes
routing security. For example, the DRR routing option provides the
information about the route back to the source. According to
Section 13.6 of [RFC6940], the base draft the enter entire DRR routing message MUST be
digitally signed and sent over by via a protected channel to protect the
DRR routing information.

8. IANA considerations Considerations

8.1. A new New RELOAD forwarding option Forwarding Option

A new RELOAD Forwarding Option type is has been added to the "RELOAD
Forwarding Option
Registry Option" registry defined in [I-D.ietf-p2psip-base].

Type: 0x02 - [RFC6940].

Code: 2
Forwarding Option: extensive_routing_mode

8.2. A new New IETF XML registry

This section requests Registry

IANA to register has registered the following URN in the "XML Namespaces" class
of the "IETF XML Registry" in accordance with [RFC3688].

URI: urn:ietf:params:xml:ns:p2p:route-mode

Registrant Contact: The IESG

XML: This specification

9. Acknowledgments

David Bryan has helped extensively with this document, 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, Stephane Bryant, Marc Petit-Huguenin Petit-Huguenin, and Carlos
Jesus Bernardos Cano for their constructive comments.

10. References

10.1. Normative references References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, RFC 2119, March 1997.

[I-D.ietf-p2psip-base]

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.

[RFC6940] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-26 (work in
progress), February 2013.

[RFC3688] Mealling, M., "The IETF XML Registry ", BCP 81, RFC3688, RFC 6940, January 2004. 2014.

10.2. Informative references References

[Chord] Stoica, I., Morris, R., Liben-Nowell, D., Karger, D.,
Kaashoek, M., Dabek, F., and H. Balakrishnan, "Chord: A
Scalable Peer-to-Peer Lookup Protocol for Internet
Applications", IEEE/ACM Transactions on Networking
Volume 11, Issue 1, 17-32, February 2003.

[DTLS] Modadugu, N., N. and E. Rescorla, E., "The Design and
Implementation of Datagram TLS", Proc. 11th Network and
Distributed System Security Symposium (NDSS),
February 2004.

[IGD2] UPnP Forum, "WANIPConnection:2 Service", September 2010,
<http://upnp.org/specs/gw/
UPnP-gw-WANIPConnection-v2-Service.pdf>.

[RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral
Self-Address Fixing (UNSAF) Across Network Address
Translation", RFC 3424, November 2002.

[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using STUN", RFC5780, Session Traversal Utilities for NAT (STUN)",
RFC 5780, May 2010.

[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-11 (work in progress), October 2013.

[IGD2] UPnP Forum, "WANIPConnection:2 Service (http://upnp.org/specs/
gw/UPnP-gw-WANIPConnection-v2-Service.pdf)", September 2010.

[RFC6886] Cheshire, S., Krochmal M., S. and K. Sekar, M. Krochmal, "NAT Port Mapping Protocol
(NAT-PMP)", RFC6886, RFC 6886, April 2013.

[RFC3424] Daigle, L., "IAB Considerations for UNilateral Self-Address
Fixing (UNSAF) Across Network Address Translation", RFC3424, November
2002.

12. References

[RFC7264] Zong, N., Jiang, X., Even, R., and Y. Zhang, "An Extension
to the REsource LOcation And Discovery (RELOAD) Protocol
to Support Relay Peer Routing", RFC 7264, June 2014.

[wikiChord]
Wikipedia, "Chord (peer-to-peer)", 2013,
<http://en.wikipedia.org/w/
index.php?title=Chord_%28peer-to-peer%29&oldid=549516287>.

Appendix A. Optional methods Methods to investigate peer connectivity Investigate Peer Connectivity

This section is for informational purposes only for providing and provides some
mechanisms that can be used when the configuration information does
not specify if DRR can be used. It summarizes some methods which that can
be used for by a peer to determine its own network location compared 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
if
whether a peer is publically publicly reachable, other than via out-of-band
mechanisms. This document addresses the UNSAF UNilateral Self-Address Fixing
(UNSAF) [RFC3424] concerns considerations by specifying a fallback plan to SRR [p2psip-base-draft].
[RFC6940]. SRR is not an UNSAF mechanism. The This document does not
define any new UNSAF mechanisms.

For DRR to function correctly, a peer may attempt to determine
whether it is publicly reachable. If it is not, the peers peer should fall
back to SRR. If the peer believes it is publically publicly reachable, DRR may
be attempted. NATs and firewalls are two major contributors to
preventing DRR from functioning properly. There are a 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
peer can perform further tests to learn whether the reflexive address
is publicly reachable. If the address appears to be publicly
reachable, the peers peer to which the address belongs can use DRR for
responses.

Some conditions that are unique in P2PSIP architecture which could be
leveraged to facilitate the tests. In a P2P overlay network, each
peer
only has partial only a partial view of the whole network, network and knows of a few
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
no direct connection. This makes it easy for a peer to ask other
peers to send unsolicited messages back to the requester.

In the following sections, we first introduce several ways for a peer
to get the addresses needed for further tests. Then Then, a test for
learning whether a peer may be publicly reachable is proposed.

A.1. Getting addresses Addresses to be used Be Used as candidates Candidates for DRR

In order to test whether a peer may be publicly reachable, the peer
should first get one or more addresses which that will be used by other
peers to send him messages directly. This address is either a local
address of a peer or a translated address which that is assigned by a NAT
to the peer.

STUN

Session Traversal Utilities for NAT (STUN) is used to get a reflexive
address on the public side of a NAT with the help of STUN servers. Discovery of
NAT behavior discovery using STUN is specified in [RFC5780]. Under
the RELOAD architecture, a few infrastructure servers can be
leveraged for discovering NAT behavior, such as enrollment servers,
diagnostic servers, bootstrap servers, etc.

The peer can use a STUN Binding request to one of the STUN servers to
trigger a STUN Binding response 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 peer can
determine that there likely is likely no NAT between it and the chosen
infrastructure server 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.). end.) Usually, these
infrastructure severs servers are publicly reachable in the overlay, so the
peer can be considered publicly reachable. On the other hand, with using
the techniques in [RFC5780], a peer can also decide whether it is
behind a NAT with endpoint-independent mapping behavior. If the peer
is behind a NAT with endpoint- independent endpoint-independent mapping behavior, the
reflexive address should also be a candidate for further tests.

UPnP-IGD

The Universal Plug and Play Internet Gateway Device (UPnP-IGD) [IGD2]
is a mechanism that a peer can use to get the assigned address from
its residential gateway gateway, and after obtaining this address to
communicate it with other peers, the peer can receive unsolicited
messages from outside, even though it is behind a NAT.
So So, the
address obtained through the UPnP mechanism should also be used for
further tests.

Another way that a peer behind NAT can use to learn its assigned address by
NAT is NAT-PMP via the NAT Port Mapping Protocol (NAT-PMP) [RFC6886]. Like in As
with 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.

A.2. Public reachability test Reachability Test

Using the transport addresses obtained by the above techniques, a
peer can start a test to learn whether the candidate transport
address is publicly reachable. The basic idea for of the test is for that a
peer to send sends a request and expect expects another peer in the overlay to send
back a response. If the response is successfully received by the
sending peer
successfully and also the peer giving the response has no direct
connection with the sending peer, the sending peer can determine that
the address is probably publicly reachable and hence the peer may be
publicly reachable at the tested transport address.

In a 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 peer. Especially in
RELOAD architecture, every Every peer
maintains a connection table. So table, particularly in the RELOAD
architecture, so it is easier for a peer to check see whether it has direct
connection with another peer.

If a peer 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 storing or fetching something to/from to or from the overlay overlay,
or for locating a specific peer, instead peer; instead, it is to get a peer who can
deliver to the sending peer an unsolicited response and which who has no
direct connection with him. Each intermediate peer receiving the
request first checks to see whether it has a direct connections connection 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 peer 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 transactions.

Appendix B. Comparison on cost of Cost of SRR and DRR

The major advantages in advantage of using DRR are in going through less is that it reduces the number of
intermediate peers on traversed by the response. By doing that it This reduces the
load on those peers' resources like load,
such as processing and communication
bandwidth. bandwidth, on those peers'
resources.

B.1. Closed or managed networks Managed Networks

As described in Section 3, many P2P systems run in a closed or
managed environment (e.g., carrier networks) networks), so that network
administrators would know that they could safely use DRR.

SRR brings out uses more routing hops than DRR. Assuming that there are N peers
in the P2P system and Chord [Chord] [wikiChord] is applied for
routing, the number of hops for a response in SRR and in DRR are
listed in the following table. Establishing a secure connection
between the sending peer and the responding peer with (D)TLS Transport Layer
Security (TLS) or Datagram TLS (DTLS) requires multiple messages.
Note that establishing (D)TLS secure connections for a P2P overlay is
not optimal in some cases, e.g., direct response routing DRR where (D)TLS is heavy for
temporary connections. Therefore, in the following table, table we show the
cases of: of 1) no (D)TLS in DRR; DRR and 2) still using DTLS in DRR as
sub-optimal. As the worst-cost case, 7 seven (7) messages are used
during
the DTLS handshaking [DTLS]. (TLS Handshake (The TLS handshake is a two round-trip negotiation
protocol that requires two (2) round trips, while the DTLS handshake
is a three round-trip negotiation protocol.) protocol that requires three (3) round trips.)

Mode | Success | No. of Hops | No. of Msgs
----------------------------------------------------
------------------------------------------------
SRR | Yes | log(N) | log(N)
DRR | Yes | 1 | 1
DRR(DTLS)
DRR (DTLS) | Yes | 1 | 7+1

Table 1. 1: Comparison of SRR and DRR in closed networks Closed Networks

From the above comparison, it is clear that:

1) In most cases when N the number of peers (N) > 2 (2^1), DRR 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 DRR in the cases where the resources such resources
as CPU and bandwidth are limited, e.g., the case of mobile,
wireless networks.

2) In the cases when N > 256 (2^8), DRR also uses fewer messages
than SRR.

3) In the cases when N < 256, DRR uses more messages than SRR (but
still uses fewer hops than SRR). So SRR), so the consideration on of whether
using
to use DRR or SRR depends on other factors like such as using less
resources (bandwidth and processing) from the intermediate peers.
Section 4 provides use cases where DRR has a better chance to work of
working or where the considerations of intermediary resources considerations are
important.

B.2. Open networks Networks

In open networks (e.g., the Internet) where DRR is not guaranteed to
work, DRR can fall back to SRR if it fails after trial, as described
in Section 4. Based on the same settings as those listed in Section 5.1,
Appendix B.1, the number of hops, as well as the number of messages
for a response in SRR and DRR DRR, are listed in the following table. table:

Table 2. 2: Comparison of SRR and DRR in open networks Open Networks

From the above comparison, it can be observed that trying to first
use DRR could still provide an overall number of hops lower than
directly using SRR. Suppose that P peers are publicly reachable, reachable; the
number of hops in DRR and SRR is P*1+(N-P)*(1+logN), P*1+(N-P)*(1+logN) and 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 (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 improves as the scale
of the network increases.

Authors' Addresses

Ning Zong (editor)
Huawei Technologies

Email:

EMail: zongning@huawei.com

Xingfeng Jiang
Huawei Technologies

Email:

EMail: jiang.x.f@huawei.com
Roni Even
Huawei Technologies

Email:

EMail: roni.even@mail01.huawei.com

Yunfei Zhang
CoolPad

Email: / China Mobile

EMail: hishigh@gmail.com