One document matched: draft-jiang-p2psip-relay-02.txt
Differences from draft-jiang-p2psip-relay-01.txt
P2PSIP X. Jiang
Internet-Draft Huawei Tech.
Intended status: Standards Track R. Even
Expires: November 30, 2009 Gesher Erove
D. Bryan
Cogent Force, LLC
May 29, 2009
An extension to RELOAD to support Direct Response and Relay Peer routing
draft-jiang-p2psip-relay-02.txt
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Abstract
This document proposes an extension to RELOAD to support direct
response and relay peer routing modes. RELOAD recommends symmetric
recursive routing for routing messages. The new extensions provide a
shorter route for responses and describes the potential cases where
these extensions can be used.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 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
3.1.3. Relay Peer Routing (RPR) . . . . . . . . . . . . . . . 7
3.2. Scenarios Where DRR can be Used . . . . . . . . . . . . . 8
3.2.1. Managed or Closed P2P System . . . . . . . . . . . . . 8
3.2.2. Wireless Scenarios . . . . . . . . . . . . . . . . . . 8
3.3. Scenarios Where RPR Benefits . . . . . . . . . . . . . . . 9
3.3.1. Managed or Closed P2P System . . . . . . . . . . . . . 9
3.3.2. Using Bootstrap Peers as Relay pPeers . . . . . . . . 9
3.3.3. Wireless Scenarios . . . . . . . . . . . . . . . . . . 9
4. Relationship Between SRR and DRR/RPR . . . . . . . . . . . . . 9
4.1. How DRR Works . . . . . . . . . . . . . . . . . . . . . . 9
4.2. How RPR Works . . . . . . . . . . . . . . . . . . . . . . 9
4.3. How These Three Routing Modes Work Together . . . . . . . 10
5. Extensions to RELOAD . . . . . . . . . . . . . . . . . . . . . 11
5.1. Basic Requirements . . . . . . . . . . . . . . . . . . . . 11
5.2. Modification To RELOAD Message Structure . . . . . . . . . 11
5.2.1. State-keeping Flag . . . . . . . . . . . . . . . . . . 11
5.2.2. Extensive Routing Mode . . . . . . . . . . . . . . . . 12
5.3. Creating a Request . . . . . . . . . . . . . . . . . . . . 13
5.3.1. Creating a Request in DRR . . . . . . . . . . . . . . 13
5.3.2. Procedure For Running RPR . . . . . . . . . . . . . . 13
5.4. Request And Response Processing . . . . . . . . . . . . . 14
5.4.1. Destination Peer: Receiving a Request And Sending
a Response . . . . . . . . . . . . . . . . . . . . . . 14
5.4.2. Sending Peer: Receiving a Response . . . . . . . . . . 14
5.4.3. Relay Peer Processing . . . . . . . . . . . . . . . . 15
6. Discovery Of Relay Peer . . . . . . . . . . . . . . . . . . . 15
7. Optional Methods to Investigate Node Connectivity . . . . . . 15
7.1. Getting Addresses To Be Used As Candidates for DRR . . . . 16
7.2. Public Reachability Test . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9.1. A new RELOAD Forwarding Option . . . . . . . . . . . . . . 18
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
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 B in
[I-D.ietf-p2psip-base]. As we show in section 3, DRR and RPR are
advantageous over RPR in some scenarios. For example, in a closed
network where every node is in the same address realm, DRR performs
better than SRR. On the other hand, 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, uisng
these three routing modes together is more likely to bring benefits
than if SRR is used alone.
In this draft, we first discuss the problem statement, then the
relationship between the three routing modes is presented. An
extension to RELOAD to support DRR and RPR is proposed in Section 5.
Section 7 gives some information on how peers can adaptively choose
the best routing mode among SRR, DRR and RPR based on existing
mechanisms.
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.
o 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.
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o Relay Peer: A type of publicly reachable peer that can receive
unsolicited messages from all other nodes in the overlay and
forward the responses from destination peers towards the request
sender.
o 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.
o 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 who will forward the responses towards the sending
peer. For simplicity, the abbreviation RPR is used instead in the
following text.
o Symmetric Recursive Routing(SRR): refers to a routing mode in
which responses follow the same request path in the reverse order
to get back to the sending peer. For simplicity, the abreviation
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 intendeded to provide public service. Some run in closed
networks of small scale. SRR works in any situation, but DRR and RPR
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 three routing modes: SRR, DRR and RPR.
Some assumptions are made in the following illustrations.
o Peer A sends a request destined to a peer who is the reponsible
peer for Resource-ID k;
o Peer X is the root peer being responsible for resource k;
o 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 for the peer from whom they got the request in the via-
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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.
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, therefore transaction efficiency will be better
than in SRR. Note, however, DRR may not always work in the presence
of NATs or other situations where network connectivity is asymmetric.
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A B C D X
| Request | | | |
|----------->| | | |
| | Request | | |
| |----------->| | |
| | | Request | |
| | |----------->| |
| | | | Request |
| | | |----------->|
| | | | |
| | | | |
| | | | |
| | | | |
| | Response| | |
|<-----------+------------+------------+------------|
| | | | |
3.1.3. Relay Peer Routing (RPR)
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 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.
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A B C D X R
| Request | | | | |
|----------->| | | | |
| | Request | | | |
| |----------->| | | |
| | | Request | | |
| | |----------->| | |
| | | | Request | |
| | | |----------->| |
| | | | | Response |
| | | | |---------->|
| | | | | |
| | | | | |
| | | Response | | |
|<-----------+------------+------------+------------+-----------|
| | | | | |
3.2. Scenarios Where DRR can be Used
This section lists several scenarios where using DRR would work, and
where 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.
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 to reduce radio
battery usage by the intermediary peers. The service provider may
recommend in the configuration using DRR based on his knowledge of
the topology.
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3.3. Scenarios Where RPR Benefits
In this section, we will list several scenarios where using RPR would
provide improved performance. Note that RPR allows a shorter
response path compared to SRR.
3.3.1. Managed or Closed P2P System
As described in Section 3.2.1, 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. As with DRR, peers must also support
SRR in case RPR fails.
3.3.2. Using Bootstrap Peers as Relay pPeers
Bootstrap peers must be publicly reachable in a RELOAD architecture.
As a result, one possible architecture would be to use the bootstrap
peers as relay peers for use with RPR. The requirements for being a
relay peer are publicly reachability and maintaining a direct
connection with its client. As such, bootstrap peers are well suited
to play the role of relay peers.
3.3.3. Wireless Scenarios
While some mobile deployments may use clients, in mobile networks
using peers, RPR, like DRR, may reduce radio battery usage by the
intermediary peers. The service provider may recommend in the
configuration using RPR based on his knowledge of the topology.
4. Relationship Between SRR and DRR/RPR
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 RPR Works
RPR is a bit more complicated than DRR. 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
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using the Attach method.
A requirement for RPR is for the source peer to convey their relay
peer (or peers) information in the request, so the destination peer
knows where the relay peer are and send the response to a relay peer
first.
(Editor's Note: Being a relay peer does not require that the relay
peer have 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.)
4.3. How These Three Routing Modes Work Together
DRR and RPR are not intended to replace SRR. As seen from Section 3,
DRR or RPR have better performance in some scenarios, but have
limitations as well. As a result, it is better to use these three
modes together to adapt to each peer's specific situation. In this
section, we give some suggestions on how to transition between the
routing modes in RELOAD.
Editor's Note: What this draft proposes are extensions to support
DRR/RPR. It is not required that the implementation should use the
strategy described to choose the appropriate mode.
A peer can collect statistical data on the success of the different
routing modes based on previous transactions. 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 or RPR. Based on the success rate as seen from the
lost message statistics, the node can either continue to offer DRR/
RPR first or switch to SRR.
The node can decide whether to try DRR or RPR 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. if a relay peer is provided by the service provider, nodes may
prefer RPR over SRR.
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5. Extensions to RELOAD
Adding support for DRR and RPR requires extensions to the current
RELOAD protocol. In this section, we detail the changes required to
the protocol, including changes to message structure and to message
processing.
5.1. Basic Requirements
All peers implementing DRR or RPR MUST support SRR.
All peers MUST be able to process requests for routing in SRR, and
MAY support DRR or RPR routing requests.
Peers that do not support or do not wish to provide DRR or RPR MAY
reject these messages.
5.2. Modification To RELOAD Message Structure
RELOAD provides an extensible framework to accommodate future
extensions. In this section, we define a ForwardingHeader structure
to support DRR and RPR modes. 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
RELOAD allows intermediate peers to maintain state in order to
implement SRR, for example for implementing hop-by-hop
retransmission. If DRR or RPR 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 should be maintained in the intermediate
peers.
[Editor's note: this flag will be useful for other cases so the
authors suggest adding it in the base draft directly as a flag in the
Forwarding Header (section 5.3.2 of that draft)]
flag : 0x3 IGNORE-STATE-KEEPING
If IGNORE-STATE-KEEPING is set, any peer receiving this message and
which is not the destination of the message MUST forward the message
as usual, but MUST not maintain any internal state. [Editors Note:
This language needs work, but we are leaving it informal here,
expecting it to be included in the base draft. Need to specify how
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this interacts with hop-by-hop reliability, and if not included in
the base, behavior if unsupported]
5.2.2. Extensive Routing Mode
This draft introduces a new forwarding option for an extensive
routing mode. This option conforms to the description in section
5.3.2.4 in [I-D.ietf-p2psip-base].
We first define a new type to define the new option,
EXTENSIVE_ROUTING_MODE_TYPE:
The new routing mode specifies that the message SHOULD be rejected in
the case it is not understood by intermediate peers, and so the
DESTINATION_CRITICAL flag is used. [Editors Note: Is this the right
behavior here?]
flag : 0x02 DESTINATION_CRITICAL
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>;
} 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-base].
Route mode: refers to which type of routing mode is indicated to the
destination peer. Currently, only DRR and RPR are defined.
Transport: refers to the transport type which is used to deliver
responses from the destination peer to the sending peer or the relay
peer;
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IpAddressPort: refers to the transport address the destination peer
is using to send the response to.
Destination: refers to the relay peer or the sending node itself. if
the routing mode is DRR, then the destination only contains the
sending node's node-id; If the routing mode is RPR, then the
destination contains two destinations, which are the relay peer's
node-id and the sending node's node-id;
5.3. Creating a Request
5.3.1. Creating a Request in 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:
o The type MUST be set to EXTENSIVE_ROUTING_MODE_TYPE
o The ExtensiveRoutingModeOption structure MUST be used for the
option field within the ForwardingOptions structure. The fields
MUST be defined as follows:
* RouteMode set to 0x01 (DRR)
* Transport set as appropriate for the sender
* IPAddressPort set to the peer's associated transport address
* The destination structure MUST contain one vaule, defined as
type peer and set with the sending peer's own values
5.3.2. Procedure For Running 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:
o The type MUST be set to EXTENSIVE_ROUTING_MODE_TYPE
o The ExtensiveRoutingModeOption structure MUST be used for the
option field within the ForwardingOptions structure. The fields
MUST be defined as follows:
* RouteMode set to 0x02 (RPR)
* Transport set as appropriate for the relay peer
* IPAddressPort set to the transport address of the relay peer
that the sender wishes the message to be relayed through
* Destination structure MUST contain two values. The first MUST
be defined as type peer and set with the values for the relay
peer. The second MUST be defined as type peer and set with the
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sending peer's own values
5.4. Request And Response Processing
This section gives normative text for message processing after DRR
and RPR are introduced. Here, we only describe the additional
procedures for supporting DRR and RPR. Please refer to
[I-D.ietf-p2psip-base] for RELOAD base procedures.
5.4.1. 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 a error response 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.
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 node node-id from the option of the
request.
In the event that the routing mode is set to DRR and there is not
exactly one destination, or the routing mode is set to RPR and there
are not exactly two destinations the destination peer MUST try to
send a error response 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 option.
5.4.2. 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.
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.
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5.4.3. Relay Peer Processing
Relay peers are designed to forward responses to nodes who are not
publicly reachable. For the routing of the response, this draft
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. However, it MUST use
the second field in the destination of the ExtensiveRoutingModeOption
to determine the destination.
6. Discovery Of Relay Peer
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].
Editor note: This section will be extended if we adopt RPR, but like
other configuration information, there may be many ways to obtain
this.
7. Optional Methods to Investigate Node Connectivity
This section is for informational purposes only for the cases when
the configuration information does not specify if DRR or RPR 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
help a node 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 resort to SRR routing in the event other routing mechanisms
fail or testing falsely indicates a node is public.
For DRR and RPR to function correctly, a node may attempt to
determine whether it is publicly reachable. If it is not, RPR should
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be chosen to route the response with the help from relay peers, or
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 and RPR 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 and also can be a candidate to
serve as a relay peer. Nodes which are not publicly reachable may
still use RPR to shorten the response path with the help from relay
peers.
There are a number of techniques with a node can ues to obtain its
reflexive address which is 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 proves publicly reachable, the nodes to which the address
belongs can use DRR for responses and also can be a candidate for
relay peer. Nodes that are not publicly reachable may still use RPR
to shorten response path with the help of relay peers.
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 get 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
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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
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 Reachability Test
Using the transport addresses obtained by means of 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
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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 and
RPR. The following text is informative.
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, and may
advertise that it is a candidate to serve as a relay peer.
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: 0x1 - extensive_routing_mode
10. Acknowledgements
Authors would like to thank Ted Hardie, Narayanan Vidya and Dondeti
Lakshminath for their comments. Special thanks go to Bruce Lowekamp
for his constructive comments.
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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-02 (work in
progress), March 2009.
[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-02 (work in progress),
July 2008.
[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.
[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.
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Authors' Addresses
XingFeng Jiang
Huawei Tech.
Huihong Mansion,No.91 Baixia Rd.
Nanjing, Jiangsu 210001
P.R.China
Phone: +86(25)84565867
Email: jiang.x.f@huawei.com
Roni Even
Gesher Erove
14 David Hamelech
Tel Aviv 64953
Israel
Email: ron.even.tlv@gmail.com
David A. Bryan
Cogent Force, LLC
Williamsburg, Virginia
United States of America
Email: dbryan@ethernot.org
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