Internet DRAFT - draft-ietf-p2psip-rpr
draft-ietf-p2psip-rpr
P2PSIP N. Zong, Ed.
Internet-Draft X. Jiang
Intended status: Standards Track R. Even
Expires: April 24, 2014 Huawei Technologies
Y. Zhang
CoolPad
October 21, 2013
An Extension to REsource LOcation And Discovery (RELOAD) Protocol to
Support Relay Peer Routing
draft-ietf-p2psip-rpr-11
Abstract
This document proposes an optional extension to REsource LOcation And
Discovery (RELOAD) protocol to support relay peer routing mode.
RELOAD recommends symmetric recursive routing for routing messages.
The new optional extension provides a shorter route for responses
reducing the overhead on intermediate peers and describes the
potential use cases where this extension can be used.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. RPR . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Scenarios where RPR can be used . . . . . . . . . . . . . 5
3.2.1. Managed or closed P2P systems . . . . . . . . . . . . 5
3.2.2. Using bootstrap nodes as relay peers . . . . . . . . 5
3.2.3. Wireless scenarios . . . . . . . . . . . . . . . . . 6
4. Relationship between SRR and RPR . . . . . . . . . . . . . . 6
4.1. How RPR works . . . . . . . . . . . . . . . . . . . . . . 6
4.2. How SRR and RPR work together . . . . . . . . . . . . . . 6
5. Comparison on cost of SRR and RPR . . . . . . . . . . . . . . 7
5.1. Closed or managed networks . . . . . . . . . . . . . . . 7
5.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 7
6. RPR extensions to RELOAD . . . . . . . . . . . . . . . . . . 8
6.1. Basic requirements . . . . . . . . . . . . . . . . . . . 8
6.2. Modification to RELOAD message structure . . . . . . . . 8
6.2.1. State-keeping flag . . . . . . . . . . . . . . . . . 8
6.2.2. Extensive routing mode . . . . . . . . . . . . . . . 9
6.3. Creating a request . . . . . . . . . . . . . . . . . . . 9
6.3.1. Creating a request for RPR . . . . . . . . . . . . . 9
6.4. Request and response processing . . . . . . . . . . . . . 10
6.4.1. Destination peer: receiving a request and sending a
response . . . . . . . . . . . . . . . . . . . . . . 10
6.4.2. Sending peer: receiving a response . . . . . . . . . 11
6.4.3. Relay peer processing . . . . . . . . . . . . . . . . 11
7. Overlay configuration extension . . . . . . . . . . . . . . . 11
8. Discovery of relay peers . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
10.1. A new RELOAD Forwarding Option . . . . . . . . . . . . . 12
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . 12
12.2. Informative References . . . . . . . . . . . . . . . . . 12
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Optional methods to investigate peer connectivity . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
REsource LOcation And Discovery (RELOAD) protocol [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 A of [I-D.ietf-p2psip-base]. As
we show in section 3, RPR is advantageous over SRR in some scenarios
reducing load (CPU and link bandwidth) on intermediate peers. RPR
works better in a network where relay peers are provisioned in
advance so that relay peers are publicly reachable in the P2P system.
In other scenarios, using a combination of RPR and SRR together is
more likely to bring benefits than if SRR is used alone.
Note that in this document, we focus on RPR routing mode and its
extensions to RELOAD to produce a standalone solution. Please refer
to DRR document [I-D.ietf-p2psip-drr] for DRR routing mode.
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
comparison on the cost of SRR and RPR in both managed and open
networks. An extension to RELOAD to support RPR is proposed in
Section 6. Discovery of relay peers is introduced in Section 7.
Some optional methods to check peer connectivity are introduced in
Appendix A.
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] extensively in this document. We also use
terms defined in NAT behavior discovery [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" does not mean that the peers must be on the
public Internet, because the RELOAD protocol may be used in a
closed network.
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Relay Peer: A type of publicly reachable peer that can receive
unsolicited messages from all other peers in the overlay and
forward the responses from destination peers towards the sender of
the request.
Relay Peer Routing (RPR): refers to a routing mode in which
responses to P2PSIP requests are sent by the destination peer to a
relay peer transport address who will forward the responses
towards the sending peer. For simplicity, the abbreviation RPR is
used instead in the rest of the document.
Symmetric Recursive Routing (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 is used
instead in the rest of the 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 system intended to provide public service, while others run in
closed networks of small scale. SRR works in any situation, but RPR
may work better in some specific scenarios.
3.1. RPR
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 RPR. Note that the same illustrative settings can be
found in DRR document [I-D.ietf-p2psip-drr].
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
RPR. Assume A is associated with relay peer R. When sending the
request, peer A includes information describing peer R transport
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
the existing connection. Figure 1 illustrates RPR. Note that RPR
also allows a shorter route for responses compared to SRR, which
means less overhead on intermediate peers. Establishing a connection
to the relay with TLS requires multiple round trips. Please refer to
Section 5 for cost comparison between SRR and RPR.
A B C D X R
| Request | | | | |
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|----------->| | | | |
| | Request | | | |
| |----------->| | | |
| | | Request | | |
| | |----------->| | |
| | | | Request | |
| | | |----------->| |
| | | | | Response |
| | | | |---------->|
| | | | Response | |
|<-----------+------------+------------+------------+-----------|
| | | | | |
Figure 1. RPR routing mode
This technique relies on the relative population of peers such as A
that require relay peers, and peers such as R that are capable of
serving as a relay peers. It also requires a mechanism to enable
peers to know which peers can be used as their relays. This
mechanism may be based on configuration, for example as part of the
overlay configuration an initial list of relay peers can be supplied.
Another option is in a response message, the responding peer can
announce that it can serve as a relay peer.
3.2. Scenarios where RPR can be used
In this section, we will list several scenarios where using RPR would
provide an improved performance.
3.2.1. Managed or closed P2P systems
As described in Section 3.2.1 of DRR draft [I-D.ietf-p2psip-drr],
many P2P systems run in a closed or managed environment so that
network administrators can better manage their system. For example,
the network administrator can deploy several relay peers which are
publicly reachable in the system and indicate their presence in the
configuration file. After learning where these relay peers are,
peers behind NATs can use RPR with the help from these relay peers.
Peers MUST also support SRR in case RPR fails.
Another usage is to install relay peers on the managed network
boundary allowing external peers to send responses to peers inside
the managed network.
3.2.2. Using bootstrap nodes as relay peers
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Bootstrap nodes are typically publicly reachable in a RELOAD
architecture. As a result, one possible architecture would be to use
the bootstrap nodes as relay peers for use with RPR. A relay peer
SHOULD be publicly accessible and maintain a direct connection with
its client. As such, bootstrap nodes are well suited to play the
role of relay peers.
3.2.3. Wireless scenarios
In some mobile deployments, using RPR may help reducing radio battery
usage and bandwidth by the intermediate peers. The service provider
may recommend using RPR based on his/her knowledge of the topology.
4. Relationship between SRR and RPR
4.1. How RPR works
Peers using RPR MUST maintain a connection with their relay peer(s).
This can be done in the same way as establishing a neighbor
connection between peers by using the Attach method.
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 knows where the relay peer are and send the response to a relay
peer first. The request SHOULD include also the requesting peer
information enabling the relay peer to route the response back to the
right peer.
Note that being a relay peer does not require that the relay peer has
more functionality than an ordinary peer. As discussed later, relay
peers comply with the same procedure as an ordinary peer to forward
messages. The only difference is that there may be a larger traffic
burden on relay peers. Relay peers can decide whether to accept a
new connection based on their current burden.
4.2. How SRR and RPR work together
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
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
.ietf-p2psip-drr] for more details. If a relay peer is provided by
the service provider, peers MAY prefer RPR over SRR. Otherwise,
using RPR SHOULD be discouraged in the open Internet or if the
administrator does not feel he have enough information about the
overlay. A new overlay configuration element specifying the usage of
DRR is defined in Section 7.
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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
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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
Adding support for RPR requires extensions to the current RELOAD
protocol. In this section, we define the extensions required to the
protocol, including extensions to message structure and to message
processing.
6.1. Basic requirements
All peers MUST be able to process requests for routing in SRR, and
MAY support RPR routing requests.
6.2. Modification to RELOAD message structure
RELOAD provides an extensible framework to accommodate future
extensions. In this section, we define a ForwardingOption structure
and present a state-keeping flag 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.
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6.2.2. Extensive routing mode
We first define a new type to define the new option,
extensive_routing_mode:
The option value is illustrated as below, defining the
ExtensiveRoutingModeOption structure:
enum {(0),DRR(1),RPR(2),(255)} RouteMode;
struct {
RouteMode routemode;
OverlayLinkType transport;
IpAddressPort ipaddressport;
Destination destinations<1..2^8-1>;
} ExtensiveRoutingModeOption;
Note that DRR value in RouteMode is defined in DRR document [I-D
.ietf-p2psip-drr].
RouteMode: refers to which type of routing mode is indicated to the
destination peer.
OverlayLinkType: refers to the transport type which is used to
deliver responses from the destination peer to the relay peer.
IpAddressPort: refers to the transport address that the destination
peer should use to send the response to. This will be a relay peer
address for RPR.
Destination: refers to the relay peer itself. If the routing mode is
RPR, then the destination contains two destinations, which are the
relay peer's Node-ID and the sending peer's Node-ID.
6.3. Creating a request
6.3.1. Creating a request for RPR
When using RPR 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.
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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 0x02 (RPR).
2.2) transport set as appropriate for 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.
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.
The second MUST be defined as type node and set with the sending
peer's own values.
6.4. Request and response processing
This section gives normative text for message processing after RPR is
introduced. Here, we only describe the additional procedures for
supporting RPR. Please refer to [I-D.ietf-p2psip-base] for RELOAD
base procedures.
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 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-
base]) to the sending peer.
If the routing mode is RPR, the destination peer MUST construct a
destination_list for the response with two entries. The first MUST
be set to the relay peer Node-ID from the option in the request and
the second MUST be the sending peer Node-ID from the option of the
request.
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
"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
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
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retransmit with SRR preference on the message it is trying to
response to now, the responding peer SHOULD abort the RPR 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]. If the sender used RPR and does not get a response
until the timeout, it MAY either resend the message using RPR but
with a different relay peer (if available), or resend the message
using SRR.
6.4.3. Relay peer processing
Relay peers are designed to forward responses to peers who are not
publicly reachable. For the routing of the response, this document
still uses the destination_list. The only difference from SRR is
that the destination_list is not the reverse of the via_list.
Instead, it is constructed from the forwarding option as described
below.
When a relay peer receives a response, it MUST follow the rules in
[I-D.ietf-p2psip-base]. It receives the response, validates the
message, re-adjust the destination_list and forward the response to
the next hop in the destination_list based on the connection table.
There is no added requirement for relay peer.
7. Overlay configuration extension
This document uses the new RELOAD overlay configuration element,
"route-mode", inside each "configuration" element, as defined in
Section 7 of the DRR document [I-D.ietf-p2psip-drr].
8. Discovery of relay peers
There are several ways to distribute the information about relay
peers throughout the overlay. P2P network providers can deploy some
relay peers and advertise them in the configuration file. With the
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
service advertisement and discovery mechanism can also be used for
discovering relay peers, for example, using the same mechanism as
used in TURN server discovery in base RELOAD [I-D.ietf-p2psip-base].
Another option is to let a peer advertise its capability to be a
relay in the response to ATTACH or JOIN.
9. Security Considerations
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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
10.1. A new RELOAD Forwarding Option
A new RELOAD Forwarding Option type is added to the Forwarding Option
Registry defined in [I-D.ietf-p2psip-base].
Type: 0x02 - extensive_routing_mode
11. Acknowledgments
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, Stephane Bryant, Marc Petit-Huguenin and
Carlos Jesus Bernardos Cano for their constructive comments.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[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-26 (work in
progress), February 2013.
[I-D.ietf-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y.,
"An extension to RELOAD to support Direct Response Routing", draft-
ietf-p2psip-drr-11 (work in progress), October 2013.
12.2. Informative References
[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using STUN", RFC5780, May 2010.
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[RFC3424] Daigle, L., "IAB Considerations for UNilateral Self-Address
Fixing (UNSAF) Across Network Address Translation", RFC3424, November
2002.
13. References
Appendix A. Optional methods to investigate peer connectivity
This section is for informational purposes only for providing some
mechanisms that can be used when the configuration information does
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
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 a peer is publically reachable, other than via out-of-band
mechanisms. This document addresses the UNSAF [RFC3424] concerns by
specifying a fallback plan to SRR [p2psip-base-draft]. SRR is not an
UNSAF mechanism. The document does not define any new UNSAF
mechanisms.
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
route the response with the help from relay peers, or the peers
should fall back to SRR. NATs and firewalls are two major
contributors preventing RPR 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 to which the address belongs can be a candidate
to serve as a relay peer. Peers which are not publicly reachable may
still use RPR to shorten the response path with the help from relay
peers.
Some conditions are unique in P2PSIP architecture which could be
leveraged to facilitate the tests. In P2P overlay network, each peer
only has partial a view of the whole 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.
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
publicly reachable is same as the DRR case. Please refer to DRR
document [I-D.ietf-p2psip-drr] for more details.
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Authors' Addresses
Ning Zong (editor)
Huawei Technologies
Email: zongning@huawei.com
Xingfeng Jiang
Huawei Technologies
Email: jiang.x.f@huawei.com
Roni Even
Huawei Technologies
Email: roni.even@mail01.huawei.com
Yunfei Zhang
CoolPad
Email: hishigh@gmail.com
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