rfc7851
Internet Engineering Task Force (IETF) H. Song
Request for Comments: 7851 X. Jiang
Category: Standards Track R. Even
ISSN: 2070-1721 Huawei
D. Bryan
ethernot.org
Y. Sun
ICT
May 2016
Peer-to-Peer (P2P) Overlay Diagnostics
Abstract
This document describes mechanisms for Peer-to-Peer (P2P) overlay
diagnostics. It defines extensions to the REsource LOcation And
Discovery (RELOAD) base protocol to collect diagnostic information
and details the protocol specifications for these extensions. Useful
diagnostic information for connection and node status monitoring is
also defined. The document also describes the usage scenarios and
provides examples of how these methods are used to perform
diagnostics.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7851.
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Diagnostic Scenarios . . . . . . . . . . . . . . . . . . . . 5
4. Data Collection Mechanisms . . . . . . . . . . . . . . . . . 6
4.1. Overview of Operations . . . . . . . . . . . . . . . . . 6
4.2. "Ping-like" Behavior: Extending Ping . . . . . . . . . . 8
4.2.1. RELOAD Request Extension: Ping . . . . . . . . . . . 9
4.3. "Traceroute-like" Behavior: The PathTrack Method . . . . 9
4.3.1. New RELOAD Request: PathTrack . . . . . . . . . . . . 10
4.4. Error Code Extensions . . . . . . . . . . . . . . . . . . 12
5. Diagnostic Data Structures . . . . . . . . . . . . . . . . . 13
5.1. DiagnosticsRequest Data Structure . . . . . . . . . . . . 13
5.2. DiagnosticsResponse Data Structure . . . . . . . . . . . 15
5.3. dMFlags and Diagnostic Kind ID Types . . . . . . . . . . 16
6. Message Processing . . . . . . . . . . . . . . . . . . . . . 19
6.1. Message Creation and Transmission . . . . . . . . . . . . 19
6.2. Message Processing: Intermediate Peers . . . . . . . . . 20
6.3. Message Response Creation . . . . . . . . . . . . . . . . 21
6.4. Interpreting Results . . . . . . . . . . . . . . . . . . 22
7. Authorization through Overlay Configuration . . . . . . . . . 23
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9.1. Diagnostics Flag . . . . . . . . . . . . . . . . . . . . 24
9.2. Diagnostic Kind ID . . . . . . . . . . . . . . . . . . . 25
9.3. Message Codes . . . . . . . . . . . . . . . . . . . . . . 26
9.4. Error Code . . . . . . . . . . . . . . . . . . . . . . . 26
9.5. Message Extension . . . . . . . . . . . . . . . . . . . . 26
9.6. XML Name Space Registration . . . . . . . . . . . . . . . 27
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1. Normative References . . . . . . . . . . . . . . . . . . 27
10.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 29
A.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 29
A.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 29
A.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 29
Appendix B. Problems with Generating Multiple Responses on Path 29
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
In the last few years, overlay networks have rapidly evolved and
emerged as a promising platform for deployment of new applications
and services in the Internet. One of the reasons overlay networks
are seen as an excellent platform for large-scale distributed systems
is their resilience in the presence of failures. This resilience has
three aspects: data replication, routing recovery, and static
resilience. Routing recovery algorithms are used to repopulate the
routing table with live nodes when failures are detected. Static
resilience measures the extent to which an overlay can route around
failures even before the recovery algorithm repairs the routing
table. Both routing recovery and static resilience rely on accurate
and timely detection of failures.
There are a number of situations in which some nodes in a Peer-to-
Peer (P2P) overlay may malfunction or behave badly. For example,
these nodes may be disabled, congested, or may be misrouting
messages. The impact of these malfunctions on the overlay network
may be a degradation of quality of service provided collectively by
the peers in the overlay network or an interruption of the overlay
services. It is desirable to identify malfunctioning or badly
behaving peers through diagnostic tools and exclude or reject them
from the P2P system. Node failures may also be caused by failures of
underlying layers. For example, recovery from an incorrect overlay
topology may be slow when the speed at which IP routing recovers
after link failures is very slow. Moreover, if a backbone link fails
and the failover is slow, the network may be partitioned, leading to
partitions of overlay topologies and inconsistent routing results
between different partitioned components.
Some keep-alive algorithms based on periodic probe and acknowledge
mechanisms enable accurate and timely detection of failures of one
node's neighbors [Overlay-Failure-Detection], but these algorithms by
themselves can only detect the disabled neighbors using the periodic
method. This may not be sufficient for the service provider
operating the overlay network.
A P2P overlay diagnostic framework supporting periodic and on-demand
methods for detecting node failures and network failures is
desirable. This document describes a general P2P overlay diagnostic
extension to the base protocol RELOAD [RFC6940] and is intended as a
complement to keep-alive algorithms in the P2P overlay itself.
Readers are advised to consult [P2PSIP-CONCEPTS] for further
background on the problem domain.
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2. Terminology
This document uses the concepts defined in RELOAD [RFC6940]. In
addition, the following terms are used in the document:
overlay hop:
One overlay hop is one portion of path between the initiator
node and the destination peer in a RELOAD overlay. Each time
packets are passed to the next node in the RELOAD overlay, one
overlay hop occurs.
underlay hop:
An underlay hop is one portion of the path between source and
destination in the IP layer. Each time packets are passed to
the next IP-layer device, an underlay hop occurs.
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 [RFC2119].
3. Diagnostic Scenarios
P2P systems are self-organizing, and ideally the setup and
configuration of individual P2P nodes requires no network management
in the traditional sense. However, users of an overlay as well as
P2P service providers may contemplate usage scenarios where some
monitoring and diagnostics are required. We present a simple
connectivity test and some useful diagnostic information that may be
used in such diagnostics.
The common usage scenarios for P2P diagnostics can be broadly
categorized in three classes:
a. Automatic diagnostics built into the P2P overlay routing
protocol. Nodes perform periodic checks of known neighbors and
remove those nodes from the routing tables that fail to respond
to connectivity checks [Handling_Churn_in_a_DHT]. Unresponsive
nodes may only be temporarily disabled, for example, due to a
local cryptographic processing overload, disk processing
overload, or link overload. It is therefore useful to repeat the
connectivity checks to see nodes have recovered and can be again
placed in the routing tables. This process is known as 'failed
node recovery' and can be optimized as described in the paper
"Handling Churn in a DHT" [Handling_Churn_in_a_DHT].
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b. Diagnostics used by a particular node to follow up on an
individual user complaint or failure. For example, a technical
support staff member may use a desktop sharing application (with
the permission of the user) to remotely determine the health of,
and possible problems with, the malfunctioning node. Part of the
remote diagnostics may consist of simple connectivity tests with
other nodes in the P2P overlay and retrieval of statistics from
nodes in the overlay. The simple connectivity tests are not
dependent on the type of P2P overlay. Note that other tests may
be required as well, including checking the health and
performance of the user's computer or mobile device and checking
the bandwidth of the link connecting the user to the Internet.
c. P2P system-wide diagnostics used to check the overall health of
the P2P overlay network. These include checking the consumption
of network bandwidth, checking for the presence of problem links,
and checking for abusive or malicious nodes. This is not a
trivial problem and has been studied in detail for content and
streaming P2P overlays [Diagnostic_Framework] and has not been
addressed in earlier documents. While this is a difficult
problem, a great deal of information that can help in diagnosing
these problems can be obtained by obtaining basic diagnostic
information for peers and the network. This document provides a
framework for obtaining this information.
4. Data Collection Mechanisms
4.1. Overview of Operations
The diagnostic mechanisms described in this document are primarily
intended to detect and locate failures or monitor performance in P2P
overlay networks. It provides mechanisms to detect and locate
malfunctioning or badly behaving nodes including disabled nodes,
congested nodes, and misrouting peers. It provides a mechanism to
detect direct connectivity or connectivity to a specified node, a
mechanism to detect the availability of specified resource records,
and a mechanism to discover P2P overlay topology and the underlay
topology failures.
The RELOAD diagnostics extensions define two mechanisms to collect
data. The first is an extension to the RELOAD Ping mechanism that
allows diagnostic data to be queried from a node as well as to
diagnose the path to that node. The second is a new method,
PathTrack, for collecting diagnostic information iteratively.
Payloads for these mechanisms allowing diagnostic data to be
collected and represented are presented, and additional error codes
are introduced. Essentially, this document reuses the RELOAD
specification [RFC6940] and extends it to introduce the new
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diagnostics methods. The extensions strictly follow how RELOAD
specifies message routing, transport, NAT traversal, and other RELOAD
protocol features.
This document primarily describes how to detect and locate failures
including disabled nodes, congested nodes, misrouting behaviors, and
underlying network faults in P2P overlay networks through a simple
and efficient mechanism. This mechanism is modeled after the ping/
traceroute paradigm: ping [RFC792] is used for connectivity checks,
and traceroute is used for hop-by-hop fault localization as well as
path tracing. This document specifies a "ping-like" mode (by
extending the RELOAD Ping method to gather diagnostics) and a
"traceroute-like" mode (by defining the new PathTrack method) for
diagnosing P2P overlay networks.
One way these tools can be used is to detect the connectivity to the
specified node or the availability of the specified resource record
through the extended Ping operation. Once the overlay network
receives some alarms about overlay service degradation or
interruption, a Ping is sent. If the Ping fails, one can then send a
PathTrack to determine where the fault lies.
The diagnostic information can only be provided to authorized nodes.
Some diagnostic information can be provided to all the participants
in the P2P overlay, and some other diagnostic information can only be
provided to the nodes authorized by the local or overlay policy. The
authorization depends on the type of the diagnostic information and
the administrative considerations and is application specific.
This document considers the general administrative scenario based on
diagnostic Kind, where a whole overlay can authorize a certain kind
of diagnostic information to a small list of particular nodes (e.g.,
administrative nodes). That means if a node gets the authorization
to access a diagnostic Kind, it can access that information from all
nodes in the overlay network. It leaves the scenario where a
particular node authorizes its diagnostic information to a particular
list of nodes out of scope. This could be achieved by extension of
this document if there is a requirement in the near future. The
default policy or access rule for a type of diagnostic information is
"deny" unless specified in the diagnostics extension document. As
the RELOAD protocol already requires that each message carries the
message signature of the sender, the receiver of the diagnostics
requests can use the signature to identify the sender. It can then
use the overlay configuration file with this signature to determine
which types of diagnostic information that node is authorized for.
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In the remainder of this section we define mechanisms for collecting
data, as well as the specific protocol extensions (message
extensions, new methods, and error codes) required to collect this
information. In Section 5 we discuss the format of the data
collected, and in Section 6 we discuss detailed message processing.
It is important to note that the mechanisms described in this
document do not guarantee that the information collected is in fact
related to the previous failures. However, using the information
from previous traversed nodes, the user (or management system) may be
able to infer the problem. Symmetric routing can be achieved by
using the Via List [RFC6940] (or an alternate DHT routing algorithm),
but the response path is not guaranteed to be the same.
4.2. "Ping-like" Behavior: Extending Ping
To provide "ping-like" behavior, the RELOAD Ping method is extended
to collect diagnostic data along the path. The request message is
forwarded by the intermediate peers along the path and then
terminated by the responsible peer. After optional local
diagnostics, the responsible peer returns a response message. If an
error is found when routing, an error response is sent to the
initiator node by the intermediate peer.
The message flow of a Ping message (with diagnostic extensions) is as
follows:
Peer A Peer B Peer C Peer D
| | | |
|(1). PingReq | | |
|------------------->|(2). PingReq | |
| |------------------->|(3). PingReq |
| | |------------------->|
| | | |
| | |<-------------------|
| |<-------------------|(4). PingAns |
|<-------------------|(5). PingAns | |
|(6). PingAns | | |
| | | |
Figure 1: Ping Diagnostic Message Flow
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4.2.1. RELOAD Request Extension: Ping
To extend the Ping request for use in diagnostics, a new extension of
RELOAD is defined. The structure for a MessageExtension in RELOAD is
defined as:
struct {
MessageExtensionType type;
Boolean critical;
opaque extension_contents<0..2^32-1>;
} MessageExtension;
For the Ping request extension, we define a new MessageExtensionType,
extension 0x2 named "Diagnostic_Ping", as specified in Table 4. The
extension contents consists of a DiagnosticsRequest structure,
defined in Section 5.1. This extension MAY be used for new requests
of the Ping method and MUST NOT be included in requests using any
other method.
This extension is not critical. If a peer does not support the
extension, they will simply ignore the diagnostic portion of the
message and will treat the message as if it were a normal ping.
Senders MUST accept a response that lacks diagnostic information and
SHOULD NOT resend the message expecting a reply. Receivers who
receive a method other than Ping including this extension MUST ignore
the extension.
4.3. "Traceroute-like" Behavior: The PathTrack Method
We define a simple PathTrack method for retrieving diagnostic
information iteratively.
The operation of this request is shown below in Figure 2. The
initiator node A asks its neighbor B which is the next hop peer to
the destination ID, and B returns a message with the next hop peer C
information, along with optional diagnostic information for B to the
initiator node. Then the initiator node A asks the next hop peer C
(direct response routing [RFC7263] or via symmetric routing) to
return next hop peer D information and diagnostic information of C.
Unless a failure prevents the message from being forwarded, this step
can be repeated until the request reaches responsible peer D for the
destination ID and retrieves the diagnostic information of peer D.
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The message flow of a PathTrack message (with diagnostic extensions)
is as follows:
Peer-A Peer-B Peer-C Peer-D
| | | |
|(1).PathTrackReq | | |
|------------------->| | |
|(2).PathTrackAns | | |
|<-------------------| | |
| |(3).PathTrackReq | |
|--------------------|------------------->| |
| |(4).PathTrackAns | |
|<-------------------|--------------------| |
| | |(5).PathTrackReq |
|--------------------|--------------------|------------------->|
| | |(6).PathTrackAns |
|<-------------------|--------------------|--------------------|
| | | |
Figure 2: PathTrack Diagnostic Message Flow
There have been proposals that RouteQuery and a series of Fetch
requests can be used to replace the PathTrack mechanism; however, in
the presence of high rates of churn, such an operation would not,
strictly speaking, provide identical results, as the path may change
between RouteQuery and Fetch operations. While obviously the path
could change between steps of PathTrack as well, with a single
message rather than two messages for query and fetch, less
inconsistency is likely, and thus the use of a single message is
preferred.
Given that in a typical diagnostic scenario the peer sending the
PathTrack request desires to obtain information about the current
path to the destination, in the event that successive calls to
PathTrack return different paths, the results should be discarded and
the request resent, ensuring that the second request traverses the
appropriate path.
4.3.1. New RELOAD Request: PathTrack
This document defines a new RELOAD method, PathTrack, to retrieve the
diagnostic information from the intermediate peers along the routing
path. At each step of the PathTrack request, the responsible peer
responds to the initiator node with requested status information.
Status information can include a peer's congestion state, processing
power, available bandwidth, the number of entries in its neighbor
table, uptime, identity, network address information, and next hop
peer information.
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A PathTrack request specifies which diagnostic information is
requested using a DiagnosticsRequest data structure, which is defined
and discussed in detail in Section 5.1. Base information is
requested by setting the appropriate flags in the data structure in
the request. If all flags are clear (no bits are set), then the
PathTrack request is only used for requesting the next hop
information. In this case, the iterative mode of PathTrack is
degraded to a RouteQuery method that is only used for checking the
liveness of the peers along the routing path. The PathTrack request
can be routed using direct response routing or other routing methods
chosen by the initiator node.
A response to a successful PathTrackReq is a PathTrackAns message.
The PathTrackAns contains general diagnostic information in the
payload, returned using a DiagnosticResponse data structure. This
data structure is defined and discussed in detail in Section 5.2.
The information returned is determined based on the information
requested in the flags in the corresponding request.
4.3.1.1. PathTrack Request
The structure of the PathTrack request is as follows:
struct{
Destination destination;
DiagnosticsRequest request;
}PathTrackReq;
The fields of the PathTrackReq are as follows:
destination: The destination that the initiator node is interested
in. This may be any valid destination object, including a NodeID,
opaque ids, or ResourceID. One example should be noted that, for
debugging purposes, the initiator will use the destination ID as
it was used when failure happened.
request: A DiagnosticsRequest, as discussed in Section 5.1.
4.3.1.2. PathTrack Response
The structure of the PathTrack response is as follows:
struct{
Destination next_hop;
DiagnosticsResponse response;
}PathTrackAns;
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The fields of the PathTrackAns are as follows:
next_hop: The information of the next hop node from the responding
intermediate peer to the destination. If the responding peer is
the responsible peer for the destination ID, then the next_hop
node ID equals the responding node ID, and after receiving a
PathTrackAns where the next_hop node ID equals the responding node
ID, the initiator MUST stop the iterative process.
response: A DiagnosticsResponse, as discussed in Section 5.2.
4.4. Error Code Extensions
This document extends the error response method defined in the RELOAD
specification to support error cases resulting from diagnostic
queries. When an error is encountered in RELOAD, the Message Code
0xffff is returned. The ErrorResponse structure includes an error
code. We define new error codes to report possible error conditions
detected while performing diagnostics:
Code Value Error Code Name
0x15 Error_Underlay_Destination_Unreachable
0x16 Error_Underlay_Time_Exceeded
0x17 Error_Message_Expired
0x18 Error_Upstream_Misrouting
0x19 Error_Loop_Detected
0x1a Error_TTL_Hops_Exceeded
The error code is returned by the upstream node before the failure
node. The upstream node uses the normal ping to detect the failure
type and return it to the initiator node, which will help the user
(initiator node) to understand where the failure happened and what
kind of error happened, as the failure may happen at the same
location and for the same reason when sending the normal message and
the diagnostics message.
As defined in RELOAD, additional information may be stored (in an
implementation-specific way) in the optional error_info byte string.
While the specifics are obviously left to the implementation, as an
example, in the case of 0x15, the error_field could be used to
provide additional information as to why the underlay destination is
unreachable (net unreachable, host unreachable, fragmentation needed,
etc.).
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5. Diagnostic Data Structures
Both the extended Ping method and PathTrack method use the following
common diagnostics data structures to collect data. Two common
structures are defined: DiagnosticsRequest for requesting data and
DiagnosticsResponse for returning the information.
5.1. DiagnosticsRequest Data Structure
The DiagnosticsRequest data structure is used to request diagnostic
information and has the following form:
enum{ (2^16-1) } DiagnosticKindId;
struct{
DiagnosticKindId kind;
opaque diagnostic_extension_contents<0..2^32-1>;
}DiagnosticExtension;
struct{
uint64 expiration;
uint64 timestamp_initiated;
uint64 dMFlags;
uint32 ext_length;
DiagnosticExtension diagnostic_extensions_list<0..2^32-1>;
}DiagnosticsRequest;
The fields in the DiagnosticsRequest are as follows:
expiration: The time when the request will expire represented as the
number of milliseconds elapsed since midnight Jan 1, 1970 UTC (not
counting leap seconds). This will have the same values for
seconds as standard UNIX time or POSIX time. More information can
be found at "Unix time" in Wikipedia [UnixTime]. This value MUST
have a value between 1 and 600 seconds in the future. This value
is used to prevent replay attacks.
timestamp_initiated: The time when the diagnostics request was
initiated, represented as the number of milliseconds elapsed since
midnight Jan 1, 1970 UTC (not counting leap seconds). This will
have the same values for seconds as standard UNIX time or POSIX
time.
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dMFlags: A mandatory field that is an unsigned 64-bit integer
indicating which base diagnostic information the request initiator
node is interested in. The initiator sets different bits to
retrieve different kinds of diagnostic information. If dMFlags is
set to zero, then no base diagnostic information is conveyed in
the PathTrack response. If dMFlags is set to all "1"s, then all
base diagnostic information values are requested. A request may
set any number of the flags to request the corresponding
diagnostic information.
Note this memo specifies the initial set of flags; the flags can
be extended. The dMflags indicate general diagnostic information.
The mapping between the bits in the dMFlags and the diagnostic
Kind ID presented is as described in Section 9.1.
ext_length: The length of the extended diagnostic request
information in bytes. If the value is greater than or equal to 1,
then some extended diagnostic information is being requested on
the assumption this information will be included in the response
if the recipient understands the extended request and is willing
to provide it. The specific diagnostic information requested is
defined in the diagnostic_extensions_list below. A value of zero
indicates no extended diagnostic information is being requested.
The value of ext_length MUST NOT be negative. Note that it is not
the length of the entire DiagnosticsRequest data structure, but of
the data making up the diagnostic_extensions_list.
diagnostic_extensions_list: Consists of one or more
DiagnosticExtension structures (see below) documenting additional
diagnostic information being requested. Each DiagnosticExtension
consists of the following fields:
kind: A numerical code indicating the type of extension
diagnostic information (see Section 9.2). Note that kinds
0xf000 - 0xfffe are reserved for overlay specific diagnostics
and may be used without IANA registration for local diagnostic
information. Kinds from 0x0000 to 0x003f MUST NOT be indicated
in the diagnostic_extensions_list in the message request, as
they may be represented using the dMFlags in a much simpler
(and more space efficient) way.
diagnostic_extension_contents: The opaque data containing the
request for this particular extension. This data is extension
dependent.
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5.2. DiagnosticsResponse Data Structure
The DiagnosticsResponse data structure is used to return the
diagnostic information and has the following form:
enum { (2^16-1) } DiagnosticKindId;
struct{
DiagnosticKindId kind;
opaque diagnostic_info_contents<0..2^16-1>;
}DiagnosticInfo;
struct{
uint64 expiration;
uint64 timestamp_initiated;
uint64 timestamp_received;
uint8 hop_counter;
uint32 ext_length;
DiagnosticInfo diagnostic_info_list<0..2^32-1>;
}DiagnosticsResponse;
The fields in the DiagnosticsResponse are as follows:
expiration: The time when the response will expire represented as
the number of milliseconds elapsed since midnight Jan 1, 1970 UTC
(not counting leap seconds). This will have the same values for
seconds as standard UNIX time or POSIX time. This value MUST have
a value between 1 and 600 seconds in the future.
timestamp_initiated: This value is copied from the diagnostics
request message. The benefit of containing such a value in the
response message is that the initiator node does not have to
maintain the state.
timestamp_received: The time when the diagnostic request was
received represented as the number of milliseconds elapsed since
midnight Jan 1, 1970 UTC (not counting leap seconds). This will
have the same values for seconds as standard UNIX time or POSIX
time.
hop_counter: This field only appears in diagnostic responses. It
MUST be exactly copied from the TTL field of the forwarding header
in the received request. This information is sent back to the
request initiator, allowing it to compute the number of hops that
the message traversed in the overlay.
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ext_length: The length of the returned DiagnosticInfo information in
bytes. If the value is greater than or equal to 1, then some
extended diagnostic information (as specified in the
DiagnosticsRequest) was available and is being returned. In that
case, this value indicates the length of the returned information.
A value of zero indicates no extended diagnostic information is
included either because none was requested or the request could
not be accommodated. The value of ext_length MUST NOT be
negative. Note that it is not the length of the entire
DiagnosticsRequest data structure but of the data making up the
diagnostic_info_list.
diagnostic_info_list: consists of one or more DiagnosticInfo
structures containing the requested diagnostic_info_contents. The
fields in the DiagnosticInfo structure are as follows:
kind: A numeric code indicating the type of information being
returned. For base data requested using the dMFlags, this code
corresponds to the dMFlag set and is described in Section 5.1.
For diagnostic extensions, this code will be identical to the
value of the DiagnosticKindId set in the "kind" field of the
DiagnosticExtension of the request. See Section 9.2.
diagnostic_info_contents: Data containing the value for the
diagnostic information being reported. Various kinds of
diagnostic information can be retrieved. Please refer to
Section 5.3 for details of the diagnostic Kind ID for the base
diagnostic information that may be reported.
5.3. dMFlags and Diagnostic Kind ID Types
The dMFlags field described above is a 64-bit field that allows
initiator nodes to identify up to 62 items of base information to
request in a request message (the first and last flags being
reserved). The dMFlags also reserves all "0"s, which means nothing
is requested, and all "1"s, which means everything is requested. But
at the same time, the first and last bits cannot be used for other
purposes, and they MUST be set to 0 when other particular diagnostic
Kind IDs are requested. When the requested base information is
returned in the response, the value of the diagnostic Kind ID will
correspond to the numeric field marked in the dMFlags in the request.
The values for the dMFlags are defined in Section 9.1 and the
diagnostic Kind IDs are defined in Section 9.2. The information
contained for each value is described in this section. Access to
each kind of diagnostic information MUST NOT be allowed unless
compliant to the rules defined in Section 7.
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STATUS_INFO (8 bits): A single-value element containing an unsigned
byte representing whether or not the node is in congestion status.
An example usage of STATUS_INFO is for congestion-aware routing.
In this scenario, each peer has to update its congestion status
periodically. An intermediate peer in the Distributed Hash
Table (DHT) network will choose its next hop according to both the
DHT routing algorithm and the status information. This is done to
avoid increasing load on congested peers. The rightmost 4 bits
are used and other bits MUST be cleared to "0"s for future use.
There are 16 levels of congestion status, with 0x00 representing
zero load and 0x0f representing congestion. This document does
not provide a specific method for congestion and leaves this
decision to each overlay implementation. One possible option for
an overlay implementation would be to take node's CPU/memory/
bandwidth usage percentage in the past 600 seconds and normalize
the highest value to the range from 0x00 to 0x0f. An overlay
implementation can also decide to not use all the 16 values from
0x00 to 0x0f. A future document may define an objective measure
or specific algorithm for this.
ROUTING_TABLE_SIZE (32 bits): A single-value element containing an
unsigned 32-bit integer representing the number of peers in the
peer's routing table. The administrator of the overlay may be
interested in statistics of this value for reasons such as routing
efficiency.
PROCESS_POWER (64 bits): A single-value element containing an
unsigned 64-bit integer specifying the processing power of the
node with MIPS as the unit. Fractional values are rounded up.
UPSTREAM_BANDWIDTH (64 bits): A single-value element containing an
unsigned 64-bit integer specifying the upstream network bandwidth
(provisioned or maximum, not available) of the node with units of
kbit/s. Fractional values are rounded up. For multihomed hosts,
this should be the link used to send the response.
DOWNSTREAM_BANDWIDTH (64 bits): A single-value element containing an
unsigned 64-bit integer specifying the downstream network
bandwidth (provisioned or maximum, not available) of the node with
kbit/s as the unit. Fractional values are rounded up. For
multihomed hosts, this should be the link the request was received
from.
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SOFTWARE_VERSION: A single-value element containing a US-ASCII
string that identifies the manufacture, model, operating system
information, and the version of the software. Given that there
are a very large number of peers in some networks, and no peer is
likely to know all other peer's software, this information may be
very useful to help determine if the cause of certain groups of
misbehaving peers is related to specific software versions. While
the format is peer defined, a suggested format is as follows:
"ApplicationProductToken (Platform; OS-or-CPU) VendorProductToken
(VendorComment)", for example, "MyReloadApp/1.0 (Unix; Linux
x86_64) libreload-java/0.7.0 (Stonyfish Inc.)". The string is a
C-style string and MUST be terminated by "\0"."\0" MUST NOT be
included in the string itself to prevent confusion with the
delimiter.
MACHINE_UPTIME (64 bits): A single-value element containing an
unsigned 64-bit integer specifying the time the node's underlying
system has been up (in seconds).
APP_UPTIME (64 bits): A single-value element containing an unsigned
64-bit integer specifying the time the P2P application has been up
(in seconds).
MEMORY_FOOTPRINT (64 bits): A single-value element containing an
unsigned 64-bit integer representing the memory footprint of the
peer program in kilobytes (1024 bytes). Fractional values are
rounded up.
DATASIZE_STORED (64 bits): An unsigned 64-bit integer representing
the number of bytes of data being stored by this node.
INSTANCES_STORED: An array element containing the number of
instances of each kind stored. The array is indexed by Kind-ID.
Each entry is an unsigned 64-bit integer.
MESSAGES_SENT_RCVD: An array element containing the number of
messages sent and received. The array is indexed by method code.
Each entry in the array is a pair of unsigned 64-bit integers
(packed end to end) representing sent and received.
EWMA_BYTES_SENT (32 bits): A single-value element containing an
unsigned 32-bit integer representing an exponential weighted
average of bytes sent per second by this peer:
sent = alpha x sent_present + (1 - alpha) x sent_last
where sent_present represents the bytes sent per second since the
last calculation and sent_last represents the last calculation of
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bytes sent per second. A suitable value for alpha is 0.8 (or
another value as determined by the implementation). This value is
calculated every five seconds (or another time period as
determined by the implementation). The value for the very first
time period should simply be the average of bytes sent in that
time period.
EWMA_BYTES_RCVD (32 bits): A single-value element containing an
unsigned 32-bit integer representing an exponential weighted
average of bytes received per second by this peer:
rcvd = alpha x rcvd_present + (1 - alpha) x rcvd_last
where rcvd_present represents the bytes received per second since
the last calculation and rcvd_last represents the last calculation
of bytes received per second. A suitable value for alpha is 0.8
(or another value as determined by the implementation). This
value is calculated every five seconds (or another time period as
determined by the implementation). The value for the very first
time period should simply be the average of bytes received in that
time period.
UNDERLAY_HOP (8 bits): Indicates the IP-layer hops from the
intermediate peer, which receives the diagnostics message to the
next-hop peer for this message. (Note: RELOAD does not require
the intermediate peers to look into the message body. So, here we
use PathTrack to gather underlay hops for diagnostics purpose).
BATTERY_STATUS (8 bits): The leftmost bit is used to indicate
whether this peer is using a battery or not. If this bit is clear
(set to "0"), then the peer is using a battery for power. The
other 7 bits are to be determined by specific applications.
6. Message Processing
6.1. Message Creation and Transmission
When constructing either a Ping message with diagnostic extensions or
a PathTrack message, the sender first creates and populates a
DiagnosticsRequest data structure. The timestamp_initiated field is
set to the current time, and the expiration field is constructed
based on this time. The sender includes the dMFlags field in the
structure, setting any number (including all) of the flags to request
particular diagnostic information. The sender MAY leave all the bits
unset, thereby requesting no particular diagnostic information.
The sender MAY also include diagnostic extensions in the
DiagnosticsRequest data structure to request additional information.
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If the sender includes any extensions, it MUST calculate the length
of these extensions and set the ext_length field to this value. If
no extensions are included, the sender MUST set ext_length to zero.
The format of the DiagnosticRequest data structure and its fields
MUST follow the restrictions defined in Section 5.1.
When constructing a Ping message with diagnostic extensions, the
sender MUST create a MessageExtension structure as defined in RELOAD
[RFC6940], setting the value of type to 0x2 and the value of critical
to FALSE. The value of extension_contents MUST be a
DiagnosticsRequest structure as defined above. The message MAY be
directed to a particular NodeID or ResourceID but MUST NOT be sent to
the broadcast NodeID.
When constructing a PathTrack message, the sender MUST set the
message_code for the RELOAD MessageContents structure to
path_track_req 0x27. The request field of the PathTrackReq MUST be
set to the DiagnosticsRequest data structure defined above. The
destination field MUST be set to the desired destination, which MAY
be either a NodeID or ResourceID but SHOULD NOT be the broadcast
NodeID.
6.2. Message Processing: Intermediate Peers
When a request arrives at a peer, if the peer's responsible ID space
does not cover the destination ID of the request, then the peer MUST
continue processing this request according to the overlay specified
routing mode from RELOAD protocol.
In P2P overlay, error responses to a message can be generated by
either an intermediate peer or the responsible peer. When a request
is received at a peer, the peer may find connectivity failures or
malfunctioning peers through the predefined rules of the overlay
network, e.g., by analyzing the Via List or underlay error messages.
In this case, the intermediate peer returns an error response to the
initiator node, reporting any malfunction node information available
in the error message payload. All error responses generated MUST
contain the appropriate error code.
Each intermediate peer receiving a Ping message with extensions (and
that understands the extension) or receiving a PathTrack request /
response MUST check the expiration value (Unix time format) to
determine if the message is expired. If the message expired, the
intermediate peer MUST generate a response with error code 0x17
"Error_Message_Expired", return the response to the initiator node,
and discard the message.
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The intermediate peer MUST return an error response with the error
code 0x15 "Error_Underlay_Destination_Unreachable" when it receives
an ICMP message with "Destination Unreachable" information after
forwarding the received request to the destination peer.
The intermediate peer MUST return an error response with the error
code 0x16 "Error_Underlay_Time_Exceeded" when it receives an ICMP
message with "Time Exceeded" information after forwarding the
received request.
The peer MUST return an error response with error code 0x18
"Error_Upstream_Misrouting" when it finds its upstream peer disobeys
the routing rules defined in the overlay. The immediate upstream
peer information MUST also be conveyed to the initiator node.
The peer MUST return an error response with error code 0x19
"Error_Loop_Detected" when it finds a loop through the analysis of
the Via List.
The peer MUST return an error response with error code 0x1a
"Error_TTL_Hops_Exceeded" when it finds that the TTL field value is
no more than 0 when forwarding.
6.3. Message Response Creation
When a diagnostic request message arrives at a peer, it is
responsible for the destination ID specified in the forwarding
header, and assuming it understands the extension (in the case of
Ping) or the new request type PathTrack, it MUST follow the
specifications defined in RELOAD to form the response header, and
perform the following operations:
o When constructing a PathTrack response, the sender MUST set the
message_code for the RELOAD MessageContents structure to
path_track_ans 0x28.
o The receiver MUST check the expiration value (Unix time format) in
the DiagnosticsRequest to determine if the message is expired. If
the message is expired, the peer MUST generate a response with the
error code 0x17 "Error_Message_Expired", return the response to
the initiator node, and discard the message.
o If the message is not expired, the receiver MUST construct a
DiagnosticsResponse structure as follows: 1) the TTL value from
the forwarding header is copied to the hop_counter field of the
DiagnosticsResponse structure (note that the default value for TTL
at the beginning represents 100 hops unless the overlay
configuration has overridden the value), and 2) the receiver
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generates a Unix time format timestamp for the current time of day
and places it in the timestamp_received field and constructs a new
expiration time and places it in the expiration field of the
DiagnosticsResponse.
o The destination peer MUST check if the initiator node has the
authority to request specific types of diagnostic information, and
if appropriate, append the diagnostic information requested in the
dMFlags and diagnostic_extensions (if any) using the
diagnostic_info_list field to the DiagnosticsResponse structure.
If any information is returned, the receiver MUST calculate the
length of the response and set ext_length appropriately. If no
diagnostic information is returned, ext_length MUST be set to
zero.
o The format of the DiagnosticResponse data structure and its fields
MUST follow the restrictions defined in Section 5.2.
o In the event of an error, an error response containing the error
code followed by the description (if they exist) MUST be created
and sent to the sender. If the initiator node asks for diagnostic
information that they are not authorized to query, the receiving
peer MUST return an error response with the error code 2
"Error_Forbidden".
6.4. Interpreting Results
The initiator node, as well as the responding peer, may compute the
overlay One-Way-Delay time through the value in timestamp_received
and the timestamp_initiated field. However, for a single hop
measurement, the traditional measurement methods (IP-layer ping) MUST
be used instead of the overlay layer diagnostics methods.
The P2P overlay network using the diagnostics methods specified in
this document MUST enforce time synchronization with a central time
server. The Network Time Protocol [RFC5905] can usually maintain
time to within tens of milliseconds over the public Internet and can
achieve better than one millisecond accuracy in local area networks
under ideal conditions. However, this document does not specify the
choice for time resolution and synchronization, leaving it to the
implementation.
The initiator node receiving the Ping response may check the
hop_counter field and compute the overlay hops to the destination
peer for the statistics of connectivity quality from the perspective
of overlay hops.
Song, et al. Standards Track [Page 22]
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7. Authorization through Overlay Configuration
Different level of access control can be made for different users/
nodes. For example, diagnostic information A can be accessed by
nodes 1 and 2, but diagnostic information B can only be accessed by
node 2.
The overlay configuration file MUST contain the following XML
elements for authorizing a node to access the relative diagnostic
Kinds.
diagnostic-kind: This has the attribute "kind" with the hexadecimal
number indicating the diagnostic Kind ID. This attribute has the
same value with Section 9.2 and at least one subelement "access-
node".
access-node: This element contains one hexadecimal number indicating
a NodeID, and the node with this NodeID is allowed to access the
diagnostic "kind" under the same diagnostic-kind element.
8. Security Considerations
The authorization for diagnostic information must be designed with
care to prevent it becoming a method to retrieve information for both
attacks. It should also be noted that attackers can use diagnostics
to analyze overlay information to attack certain key peers. For
example, diagnostic information might be used to fingerprint a peer
where the peer will lose its anonymity characteristics, but anonymity
might be very important for some P2P overlay networks, and defenses
against such fingerprinting are probably very hard. As such,
networks where anonymity is of very high importance may find
implementation of diagnostics problematic or even undesirable,
despite the many advantages it offers. As this document is a RELOAD
extension, it follows RELOAD message header and routing
specifications. The common security considerations described in the
base document [RFC6940] are also applicable to this document.
Overlays may define their own requirements on who can collect/share
diagnostic information.
Song, et al. Standards Track [Page 23]
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9. IANA Considerations
9.1. Diagnostics Flag
IANA has created a "RELOAD Diagnostics Flag" registry under protocol
RELOAD. Entries in this registry are 1-bit flags contained in a
64-bit integer dMFlags denoting diagnostic information to be
retrieved as described in Section 4.3.1. New entries SHALL be
defined via Standards Action as per [RFC5226]. The initial contents
of this registry are:
+-------------------------+----------------------------+----------+
| Diagnostic Information |Diagnostic Flag in dMFlags | Reference|
|-------------------------+----------------------------+----------|
|Reserved All 0s value | 0x 0000 0000 0000 0000 | RFC 7851 |
|Reserved First Bit | 0x 0000 0000 0000 0001 | RFC 7851 |
|STATUS_INFO | 0x 0000 0000 0000 0002 | RFC 7851 |
|ROUTING_TABLE_SIZE | 0x 0000 0000 0000 0004 | RFC 7851 |
|PROCESS_POWER | 0x 0000 0000 0000 0008 | RFC 7851 |
|UPSTREAM_BANDWIDTH | 0x 0000 0000 0000 0010 | RFC 7851 |
|DOWNSTREAM_ BANDWIDTH | 0x 0000 0000 0000 0020 | RFC 7851 |
|SOFTWARE_VERSION | 0x 0000 0000 0000 0040 | RFC 7851 |
|MACHINE_UPTIME | 0x 0000 0000 0000 0080 | RFC 7851 |
|APP_UPTIME | 0x 0000 0000 0000 0100 | RFC 7851 |
|MEMORY_FOOTPRINT | 0x 0000 0000 0000 0200 | RFC 7851 |
|DATASIZE_STORED | 0x 0000 0000 0000 0400 | RFC 7851 |
|INSTANCES_STORED | 0x 0000 0000 0000 0800 | RFC 7851 |
|MESSAGES_SENT_RCVD | 0x 0000 0000 0000 1000 | RFC 7851 |
|EWMA_BYTES_SENT | 0x 0000 0000 0000 2000 | RFC 7851 |
|EWMA_BYTES_RCVD | 0x 0000 0000 0000 4000 | RFC 7851 |
|UNDERLAY_HOP | 0x 0000 0000 0000 8000 | RFC 7851 |
|BATTERY_STATUS | 0x 0000 0000 0001 0000 | RFC 7851 |
|Reserved Last Bit | 0x 8000 0000 0000 0000 | RFC 7851 |
|Reserved All 1s value | 0x ffff ffff ffff ffff | RFC 7851 |
+-------------------------+----------------------------+----------+
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9.2. Diagnostic Kind ID
IANA has created a "RELOAD Diagnostic Kind ID" registry under
protocol RELOAD. Entries in this registry are 16-bit integers
denoting diagnostics extension data kinds carried in the diagnostic
request and response messages, as described in Sections and 5.1 and
5.2. Code points from 0x0001 to 0x003e are asked to be assigned
together with flags within the "RELOAD Diagnostics Flag" registry.
The registration procedure for the "RELOAD Diagnostic Kind ID"
registry is Standards Action as defined in RFC 5226.
+----------------------+---------------+---------------+
| Diagnostic Kind | Code | Specification |
+----------------------+---------------+---------------+
| Reserved | 0x0000 | RFC 7851 |
| STATUS_INFO | 0x0001 | RFC 7851 |
| ROUTING_TABLE_SIZE | 0x0002 | RFC 7851 |
| PROCESS_POWER | 0x0003 | RFC 7851 |
| UPSTREAM_BANDWIDTH | 0x0004 | RFC 7851 |
| DOWNSTREAM_BANDWIDTH | 0x0005 | RFC 7851 |
| SOFTWARE_VERSION | 0x0006 | RFC 7851 |
| MACHINE_UPTIME | 0x0007 | RFC 7851 |
| APP_UPTIME | 0x0008 | RFC 7851 |
| MEMORY_FOOTPRINT | 0x0009 | RFC 7851 |
| DATASIZE_STORED | 0x000a | RFC 7851 |
| INSTANCES_STORED | 0x000b | RFC 7851 |
| MESSAGES_SENT_RCVD | 0x000c | RFC 7851 |
| EWMA_BYTES_SENT | 0x000d | RFC 7851 |
| EWMA_BYTES_RCVD | 0x000e | RFC 7851 |
| UNDERLAY_HOP | 0x000f | RFC 7851 |
| BATTERY_STATUS | 0x0010 | RFC 7851 |
| Unassigned | 0x0011-0x003e | RFC 7851 |
| local use (Reserved) | 0xf000-0xfffe | RFC 7851 |
| Reserved | 0xffff | RFC 7851 |
+----------------------+---------------+---------------+
Table 1: Diagnostic Kind
Song, et al. Standards Track [Page 25]
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9.3. Message Codes
This document introduces two new types of messages and their
responses, so the following additions have been made to the "RELOAD
Message Codes" registry defined in RELOAD [RFC6940].
+-------------------+------------+----------+
| Message Code Name | Code Value | RFC |
+-------------------+------------+----------+
| path_track_req | 0x27 | RFC 7851 |
| path_track_ans | 0x28 | RFC 7851 |
+-------------------+------------+----------+
Table 2: Extensions to RELOAD Message Codes
9.4. Error Code
This document introduces the following new error codes, which have
been added to the "RELOAD Error Codes" registry.
+----------------------------------------+------------+-----------+
| Error Code Name | Code Value | Reference |
+----------------------------------------+------------+-----------+
| Error_Underlay_Destination_Unreachable | 0x15 | RFC 7851 |
| Error_Underlay_Time_Exceeded | 0x16 | RFC 7851 |
| Error_Message_Expired | 0x17 | RFC 7851 |
| Error_Upstream_Misrouting | 0x18 | RFC 7851 |
| Error_Loop_Detected | 0x19 | RFC 7851 |
| Error_TTL_Hops_Exceeded | 0x1A | RFC 7851 |
+----------------------------------------+------------+-----------+
Table 3: RELOAD Error Codes
9.5. Message Extension
This document introduces the following new RELOAD extension code:
+-----------------+------+-----------+
| Extension Name | Code | Reference |
+-----------------+------+-----------+
| Diagnostic_Ping | 0x2 | RFC 7851 |
+-----------------+------+-----------+
Table 4: New RELOAD Extension Code
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9.6. XML Name Space Registration
This document registers a URI for the config-diagnostics XML
namespace in the IETF XML registry defined in [RFC3688]. All the
elements defined in this document belong to this namespace.
URI: urn:ietf:params:xml:ns:p2p:config-diagnostics
Registrant Contact: The IESG.
XML: N/A; the requested URIs are XML namespaces
The overlay configuration file MUST contain the following XML
language declaring P2P diagnostics as a mandatory extension to
RELOAD.
<mandatory-extension>
urn:ietf:params:xml:ns:p2p:config-diagnostics
</mandatory-extension>
10. References
10.1. Normative References
[RFC792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<http://www.rfc-editor.org/info/rfc792>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>.
Song, et al. Standards Track [Page 27]
RFC 7851 P2P Overlay Diagnostics May 2016
[RFC6940] Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S.,
and H. Schulzrinne, "REsource LOcation And Discovery
(RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940,
January 2014, <http://www.rfc-editor.org/info/rfc6940>.
[RFC7263] Zong, N., Jiang, X., Even, R., and Y. Zhang, "An Extension
to the REsource LOcation And Discovery (RELOAD) Protocol
to Support Direct Response Routing", RFC 7263,
DOI 10.17487/RFC7263, June 2014,
<http://www.rfc-editor.org/info/rfc7263>.
10.2. Informative References
[UnixTime] Wikipedia, "Unix time", April 2016,
<https://en.wikipedia.org/w/
index.php?title=Unix_time&oldid=715503178>.
[P2PSIP-CONCEPTS]
Bryan, D., Matthews, P., Shim, E., Willis, D., and S.
Dawkins, "Concepts and Terminology for Peer to Peer SIP",
Work in Progress, draft-ietf-p2psip-concepts-09, April
2016.
[Overlay-Failure-Detection]
Zhuang, S., Geels, D., Stoica, I., and R. Katz, "On
failure detection algorithms in overlay networks", In
Proceedings of the IEEE INFOCOM 2005, pp. 2112-2123,
DOI 10.1109/INFCOM.2005.1498487, March 2005.
[Handling_Churn_in_a_DHT]
Rhea, S., Geels, D., Roscoe, T., and J. Kubiatowicz,
"Handling Churn in a DHT", In Proceedings of the
USENIX Annual Technical Conference, June 2004.
[Diagnostic_Framework]
Jin, X., Xiong, Y., Zhang, Q., and S. Chan, "A Diagnostic
Framework for Peer-to-peer Streaming", IEEE ICME 2006,
July 2006.
Song, et al. Standards Track [Page 28]
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Appendix A. Examples
Below, we sketch how these metrics can be used.
A.1. Example 1
A peer may set EWMA_BYTES_SENT and EWMA_BYTES_RCVD flags in the
PathTrackReq to its direct neighbors. A peer can use EWMA_BYTES_SENT
and EWMA_BYTES_RCVD of another peer to infer whether it is acting as
a media relay. It may then choose not to forward any requests for
media relay to this peer. Similarly, among the various candidates
for filling up a routing table, a peer may prefer a peer with a large
UPTIME value, small RTT, and small LAST_CONTACT value.
A.2. Example 2
A peer may set the STATUS_INFO Flag in the PathTrackReq to a remote
destination peer. The overlay has its own threshold definition for
congestion. The peer can obtain knowledge of all the status
information of the intermediate peers along the path, then it can
choose other paths to that node for the subsequent requests.
A.3. Example 3
A peer may use Ping to evaluate the average overlay hops to other
peers by sending PingReq to a set of random resource or node IDs in
the overlay. A peer may adjust its timeout value according to the
change of average overlay hops.
Appendix B. Problems with Generating Multiple Responses on Path
An earlier draft version of this document considered an approach
where a response was generated by each intermediate peer as the
message traversed the overlay. This approach was discarded. One
reason this approach was discarded was that it could provide a DoS
mechanism, whereby an attacker could send an arbitrary message
claiming to be from a spoofed "sender" the real sender wished to
attack. As a result of sending this one message, many messages would
be generated and sent back to the spoofed "sender" -- one from each
intermediate peer on the message path. While authentication
mechanisms could reduce some risk of this attack, it still resulted
in a fundamental break from the request-response nature of the RELOAD
protocol, as multiple responses are generated to a single request.
Although one request with responses from all the peers in the route
will be more efficient, it was determined to be too great a security
risk and a deviation from the RELOAD architecture.
Song, et al. Standards Track [Page 29]
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Acknowledgments
We would like to thank Zheng Hewen for the contribution of the
initial draft version of this document. We would also like to thank
Bruce Lowekamp, Salman Baset, Henning Schulzrinne, Jiang Haifeng, and
Marc Petit-Huguenin for the email discussion and their valued
comments, and special thanks to Henry Sinnreich for contributing to
the usage scenarios text. We would like to thank the authors of the
RELOAD protocol for transferring text about diagnostics to this
document.
Authors' Addresses
Haibin Song
Huawei
Email: haibin.song@huawei.com
Jiang Xingfeng
Huawei
Email: jiangxingfeng@huawei.com
Roni Even
Huawei
14 David Hamelech
Tel Aviv 64953
Israel
Email: ron.even.tlv@gmail.com
David A. Bryan
ethernot.org
Cedar Park, Texas
United States
Email: dbryan@ethernot.org
Yi Sun
ICT
Email: sunyi@ict.ac.cn
Song, et al. Standards Track [Page 30]
ERRATA
