Internet Engineering Task Force (IETF) C. Jennings

Internet Engineering Task Force (IETF) C. Jennings
Request for Comments: 7904 Cisco
Category: Standards Track B. Lowekamp
ISSN: 2070-1721 Skype
E. Rescorla
RTFM, Inc.
S. Baset
IBM
H. Schulzrinne
Columbia University
T. Schmidt, Ed.
HAW Hamburg
October 2016

A SIP Usage for REsource LOcation And Discovery (RELOAD)

Abstract

This document defines a SIP Usage for REsource LOcation And Discovery
(RELOAD). The SIP Usage provides the functionality of a SIP proxy or
registrar in a fully distributed system and includes a lookup service
for Address of Records (AORs) stored in the overlay. It also defines
Globally Routable User Agent URIs (GRUUs) that allow the
registrations to map an AOR to a specific node reachable through the
overlay. After such initial contact of a Peer, the RELOAD AppAttach
method is used to establish a direct connection between nodes through
which SIP messages are exchanged.

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 7841.

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/rfc7904.

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RFC 7904 RELOAD SIP Usage October 2016

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
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publication of this document. Please review these documents
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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.

This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.

Jennings, et al. Standards Track [Page 2]

RFC 7904 RELOAD SIP Usage October 2016

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Registering AORs in the Overlay . . . . . . . . . . . . . . . 6
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Data Structure . . . . . . . . . . . . . . . . . . . . . 7
3.3. Access Control . . . . . . . . . . . . . . . . . . . . . 9
3.4. Overlay Configuration Document Extension . . . . . . . . 10
4. Looking Up an AOR . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Finding a Route to an AOR . . . . . . . . . . . . . . . . 11
4.2. Resolving an AOR . . . . . . . . . . . . . . . . . . . . 12
5. Forming a Direct Connection . . . . . . . . . . . . . . . . . 12
5.1. Setting Up a Connection . . . . . . . . . . . . . . . . . 12
5.2. Keeping a Connection Alive . . . . . . . . . . . . . . . 13
6. Using GRUUs . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. SIP-REGISTRATION Kind Definition . . . . . . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8.1. RELOAD-Specific Issues . . . . . . . . . . . . . . . . . 14
8.2. SIP-Specific Issues . . . . . . . . . . . . . . . . . . . 15
8.2.1. Fork Explosion . . . . . . . . . . . . . . . . . . . 15
8.2.2. Malicious Retargeting . . . . . . . . . . . . . . . . 15
8.2.3. Misuse of AORs . . . . . . . . . . . . . . . . . . . 15
8.2.4. Privacy Issues . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9.1. Data Kind-ID . . . . . . . . . . . . . . . . . . . . . . 16
9.2. XML Namespace Registration . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Third-Party Registration . . . . . . . . . . . . . . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20

Jennings, et al. Standards Track [Page 3]

RFC 7904 RELOAD SIP Usage October 2016

1. Introduction

REsource LOcation And Discovery (RELOAD) [RFC6940] specifies a peer-
to-peer (P2P) signaling protocol for general use on the Internet.
This document defines a SIP Usage of RELOAD that allows SIP [RFC3261]
user agents (UAs) to establish peer-to-peer SIP (or SIPS) sessions
without the requirement for a permanent proxy or registration
servers, e.g., a fully distributed telephony service. This service
transparently supports SIP addressing including telephone numbers.
In such a network, the RELOAD overlay itself performs the
registration and rendezvous functions ordinarily associated with such
servers.

The SIP Usage involves two basic functions:

Registration: SIP UAs can use the RELOAD data storage functionality
to store a mapping from their Address of Record (AOR) to their
Node-ID in the overlay and to retrieve the Node-ID of other UAs.

Rendezvous: Once a SIP UA has identified the Node-ID for an AOR it
wishes to call, it can use the RELOAD message routing system to
set up a direct connection for exchanging SIP messages.

Mappings are stored in the SipRegistration Resource Record defined in
this document. All operations required to perform a SIP registration
or rendezvous are standard RELOAD protocol methods.

For example, Bob registers his AOR, "[email protected]", for his
Node-ID "1234". When Alice wants to call Bob, she queries the
overlay for "[email protected]" and receives Node-ID "1234" in
return. She then uses the overlay routing to establish a direct
connection with Bob and can directly transmit a standard SIP INVITE.
In detail, this works along the following steps:

1. Bob, operating Node-ID "1234", stores a mapping from his AOR to
his Node-ID in the overlay by applying a Store request for
"[email protected] -> 1234".

2. Alice, operating Node-ID "5678", decides to call Bob. She
retrieves Node-ID "1234" by performing a Fetch request on
"[email protected]".

3. Alice uses the overlay to route an AppAttach message to Bob's
Peer (ID "1234"). Bob responds with his own AppAttach and they
set up a direct connection, as shown in Figure 1. Note that
mutual Interactive Connectivity Establishment (ICE) checks are
invoked automatically from the AppAttach message exchange.

Jennings, et al. Standards Track [Page 4]

RFC 7904 RELOAD SIP Usage October 2016

Overlay
Alice Peer1 ... PeerN Bob
(5678) (1234)
-------------------------------------------------
AppAttach ->
AppAttach ->
AppAttach ->
AppAttach ->
<- AppAttach
<- AppAttach
<- AppAttach
<- AppAttach

<------------------ ICE Checks ----------------->
INVITE ----------------------------------------->
<--------------------------------------------- OK
ACK -------------------------------------------->
<------------ ICE Checks for media ------------->
<-------------------- RTP ---------------------->

Figure 1: Connection Setup in P2P SIP Using the RELOAD Overlay

It is important to note that the only role of RELOAD in this example
is to set up the direct SIP connection between Alice and Bob. As
soon as the ICE checks complete and the connection is established,
ordinary SIP or SIPS is used. In particular, the establishment of
the media channel for a phone call happens via the usual SIP
mechanisms, and RELOAD is not involved. Media never traverses the
overlay. After the successful exchange of SIP messages,
communicating Peers run ICE connectivity checks for media.

In addition to mappings from AORs to Node-IDs, the SIP Usage also
allows mappings from AORs to other AORs. This enables an indirection
useful for call forwarding. For instance, if Bob wants his phone
calls temporarily forwarded to Charlie, he can store the mapping
"[email protected] -> [email protected]". When Alice wants
to call Bob, she retrieves this mapping and can then fetch Charlie's
AOR to retrieve his Node-ID. These mechanisms are described in
Section 3.

Alternatively, Globally Routable User Agent URIs (GRUUs) [RFC5627]
can be used for directly accessing Peers. They are handled via a
separate mechanism, as described in Section 6.

Concepts used in this document can be extended to include tel URIs
[RFC3966], but this will require further specifications to ensure
semantic interoperability of implementations.

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RFC 7904 RELOAD SIP Usage October 2016

The SIP Usage for RELOAD addresses a fully distributed deployment of
session-based services among overlay Peers. This RELOAD Usage may be
relevant in a variety of environments, including a tightly controlled
environment of a single provider that admits parties using AORs with
domains from controlled namespace(s) only, or an open, multi-party
infrastructure that liberally allows a registration and rendezvous
for various or any domain namespace. It is noteworthy in this
context that -- in contrast to regular SIP -- domain names play no
role in routing to a proxy server. Once connectivity to an overlay
is given, the technology allows any name registration, possibly
constrained by overlay domain restrictions.

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 "Concepts and Terminology
for Peer-to-Peer SIP (P2PSIP)" [RFC7890] and the RELOAD Base Protocol
[RFC6940] extensively in this document.

In addition, terms defined by SIP [RFC3261] apply to this memo. The
term AOR is the SIP "Address of Record" used to identify a user in
SIP. For example, "[email protected]" could be the AOR for Alice.
For the purposes of this specification, an AOR is considered not to
include the scheme (e.g., sip:), as the AOR needs to match the
rfc822Name in the X.509 v3 certificates [RFC5280]. It is worth
noting that SIP and SIPS are distinguished in P2PSIP by the
Application-ID.

3. Registering AORs in the Overlay

3.1. Overview

In ordinary SIP, a UA registers the user's AOR and its network
location with a registrar. In RELOAD, this registrar function is
provided by the overlay as a whole. To register its location, a
RELOAD peer stores a SipRegistration Resource Record under its own
AOR using the SIP-REGISTRATION Kind, which is formally defined in
Section 7. Note that the registration lifetime known from the
regular SIP REGISTER method is inherited from the lifetime attribute
of the basic RELOAD StoredData structure (see Section 7 in
[RFC6940]).

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RFC 7904 RELOAD SIP Usage October 2016

A RELOAD overlay MAY restrict the storage of AORs. Namespaces (i.e.,
the right-hand side of the AOR) that are supported for registration
and lookup can be configured for each RELOAD deployment as described
in Section 3.4.

As a simple example, consider Alice with an AOR
"[email protected]" at Node-ID "1234". She might store the
mapping "[email protected] -> 1234" telling anyone who wants to
call her to contact node "1234".

RELOAD peers can store two kinds of SIP mappings,

o from an AOR to a destination list (a single Node-ID is just a
trivial destination list), or

o from one AOR to another.

The meaning of the first kind of mapping is "in order to contact me,
form a connection with this Peer." The meaning of the second kind of
mapping is "in order to contact me, dereference this AOR". The
latter allows for forwarding. For instance, if Alice wants her calls
to be forwarded to her secretary, Sam, she might insert the following
mapping, "[email protected] -> [email protected]".

3.2. Data Structure

This section defines the SipRegistration Resource Record as follows:

enum {
sip_registration_uri(1),
sip_registration_route(2),
(255)
} SipRegistrationType;

select (SipRegistration.type) {
case sip_registration_uri:
opaque uri<0..2^16-1>;

case sip_registration_route:
opaque contact_prefs<0..2^16-1>;
Destination destination_list<3..2^16-1>;

/* This type can be extended */

} SipRegistrationData;

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RFC 7904 RELOAD SIP Usage October 2016

struct {
SipRegistrationType type;
uint16 length;
SipRegistrationData data;
} SipRegistration;

The contents of the SipRegistration Resource Record are:

type

the type of the registration

length

the length of the rest of the PDU

data

the registration data

o If the registration is of type "sip_registration_uri", then the
contents are an opaque string containing the AOR.

o If the registration is of type "sip_registration_route", then the
contents are an opaque string containing the registrant's contact
preferences and a destination list for the Peer.

The callee expresses its capabilities within the contact preferences
as specified in [RFC3840]. It encodes a media feature set comprised
of its capabilities as a contact predicate, i.e., a string of feature
parameters that appear as part of the Contact header field. Feature
parameters are derived from the media feature set syntax of [RFC2533]
(see also [RFC2738]) as described in [RFC3840].

This encoding covers all SIP User Agent capabilities, as defined in
[RFC3840] and registered in the SIP feature tag registration tree.
In particular, a callee can indicate that it prefers contact via a
particular SIP scheme -- SIP or SIPS -- by using one of the following
contact_prefs attributes:

(sip.schemes=SIP)
(sip.schemes=SIPS)

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RFC 7904 RELOAD SIP Usage October 2016

RELOAD explicitly supports multiple registrations for a single AOR.
The registrations are stored in a dictionary with Node-IDs as the
dictionary keys. Consider, for instance, the case where Alice has
two Peers:

o her desk phone (1234)

o her cell phone (5678)

Alice might store the following in the overlay at resource
"[email protected]":

o a SipRegistration of type "sip_registration_route" with dictionary
key "1234" and value "1234", both referring to Node-IDs

o a SipRegistration of type "sip_registration_route" with dictionary
key "5678" and value "5678"

Note that this structure explicitly allows one Node-ID to forward to
another Node-ID. For instance, Alice could set calls to her desk
phone to ring at her cell phone by storing a SipRegistration of type
"sip_registration_route" with a dictionary key "1234" and a value
"5678".

3.3. Access Control

In order to prevent hijacking or other misuse, registrations are
subject to access control rules. Two kinds of restrictions apply:

o A Store is permitted only for AORs with domain names that fall
into the namespaces supported by the RELOAD Overlay Instance.

o Storing requests are performed according to the USER-NODE-MATCH
access control policy of RELOAD.

Before issuing a Store request to the overlay, any Peer SHOULD verify
that the AOR of the request is a valid Resource Name with respect to
its domain name and the namespaces defined in the overlay
configuration document (see Section 3.4).

Before a Store is permitted, the Storing Peer MUST check that:

o The AOR of the request is a valid Resource Name with respect to
the namespaces defined in the overlay configuration document.

o The certificate contains a username that is a SIP AOR that hashes
to the Resource-ID it is being stored at.

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RFC 7904 RELOAD SIP Usage October 2016

o The certificate contains a Node-ID that is the same as the
dictionary key it is being stored at.

If any of these checks fail, the request MUST be rejected with an
Error_Forbidden error.

Note that these rules permit Alice to forward calls to Bob without
his permission. However, they do not permit Alice to forward Bob's
calls to her. See Section 8.2.2 for additional details.

3.4. Overlay Configuration Document Extension

The use of a SIP-enabled overlay MAY be restricted to users with AORs
from specific domains. When deploying an overlay service, providers
can implement such restrictions by defining a set of namespaces for
admissible domain names. This section extends the overlay
configuration document by defining new elements for patterns that
describe a corresponding domain name syntax.

A RELOAD overlay can be configured to accept store requests for any
AOR, or to apply domain name restrictions. To apply restrictions,
the overlay configuration document needs to contain a <domain-
restrictions> element. The <domain-restrictions> element serves as a
container for zero to multiple <pattern> sub-elements. A <pattern>
element MAY be present if the "enable" attribute of its parent
element is set to true. Each <pattern> element defines a pattern for
constructing admissible resource names. It is of type xsd:string and
interpreted as a regular expression according to "POSIX Extended
Regular Expression" (see the specifications in [IEEE-Posix]).
Encoding of the domain name adheres to the restricted ASCII character
set without character escaping as defined in Section 19.1 of
[RFC3261].

Inclusion of a <domain-restrictions> element in an overlay
configuration document is OPTIONAL. If the element is not included,
the default behavior is to accept any AOR. If the element is
included and the "enable" attribute is not set or set to false, the
overlay MUST only accept AORs that match the domain name of the
overlay. If the element is included and the "enable" attribute is
set to true, the overlay MUST only accept AORs that match patterns
specified in the <domain-restrictions> element.

Example of Domain Patterns:
dht\.example\.com
.*\.my\.example

In this example, any AOR will be accepted that is either of the form
<user>@dht.example.com, or ends with the domain "my.example".

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RFC 7904 RELOAD SIP Usage October 2016

The RELAX NG grammar for the AOR Domain Restriction reads:

# AOR DOMAIN RESTRICTION URN SUB-NAMESPACE

namespace sip = "urn:ietf:params:xml:ns:p2p:config-base:sip"

# AOR DOMAIN RESTRICTION ELEMENT

Kind-parameter &= element sip:domain-restriction {

attribute enable { xsd:boolean }

# PATTERN ELEMENT

element sip:pattern { xsd:string }*
}?

4. Looking Up an AOR

4.1. Finding a Route to an AOR

A RELOAD user, member of an overlay, who wishes to call another user
with a given AOR SHALL proceed in the following way:

AOR is a GRUU? If the AOR is a GRUU for this overlay, the callee can
be contacted directly as described in Section 6.

AOR domain is hosted in overlay? If the domain part of the AOR
matches a domain pattern configured in the overlay, the user can
continue to resolve the AOR in this overlay. The user MAY choose
to query the DNS service records to search for additional support
of this domain name.

AOR domain not supported by overlay? If the domain part of the AOR
is not supported in the current overlay, the user might query the
DNS (or other discovery services at hand) to search for an
alternative overlay that services the AOR under request.
Alternatively, standard SIP procedures for contacting the callee
might be used.

AOR inaccessible? If all of the above contact attempts fail, the
call fails.

The procedures described above likewise apply when nodes are
simultaneously connected to several overlays.

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RFC 7904 RELOAD SIP Usage October 2016

4.2. Resolving an AOR

A RELOAD user that has discovered a route to an AOR in the current
overlay SHALL execute the following steps:

1. Perform a Fetch for Kind SIP-REGISTRATION at the Resource-ID
corresponding to the AOR. This Fetch SHOULD NOT indicate any
dictionary keys, so that it will fetch all the stored values.

2. If any of the results of the Fetch are non-GRUU AORs, then repeat
step 1 for that AOR.

3. Once only GRUUs and destination lists remain, the Peer removes
duplicate destination lists and GRUUs from the list and initiates
SIP or SIPS connections to the appropriate Peers as described in
the following sections. If there are also external AORs, the
Peer follows the appropriate procedure for contacting them as
well.

5. Forming a Direct Connection

5.1. Setting Up a Connection

Once the Peer has translated the AOR into a set of destination lists,
it then uses the overlay to route AppAttach messages to each of those
Peers. The "application" field MUST be either 5060 to indicate SIP
or 5061 to indicate SIPS. If certificate-based authentication is in
use, the responding Peer MUST present a certificate with a Node-ID
matching the terminal entry in the destination list. Otherwise, the
connection MUST NOT be used and MUST be closed. Note that it is
possible that the Peers already have a RELOAD connection mutually
established. This MUST NOT be used for SIP messages unless it is a
SIP connection. A previously established SIP connection MAY be used
for a new call.

Once the AppAttach succeeds, the Peer sends plain or (D)TLS-encrypted
SIP messages over the connection as in normal SIP. A caller MAY
choose to contact the callee using SIP or SIPS, but SHOULD follow a
preference indicated by the callee in its contact_prefs attribute
(see Section 3.2). A callee MAY choose to listen on both SIP and
SIPS ports and accept calls from either SIP scheme, or select a
single one. However, a callee that decides to accept SIPS calls
only, SHOULD indicate its choice by setting the corresponding
attribute in its contact_prefs. It is noteworthy that, according to
[RFC6940], all overlay links are built on (D)TLS-secured transport.

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RFC 7904 RELOAD SIP Usage October 2016

SIP messages carry the SIP URIs of actual overlay endpoints (e.g.,
"sip:[email protected]") in the Via and Contact headers, while
the communication continues via the RELOAD connection. However, a UA
can redirect its communication path by setting an alternate Contact
header field like in ordinary SIP.

5.2. Keeping a Connection Alive

In many cases, RELOAD connections established from ICE [RFC5245]
negotiations will traverse stateful NATs and firewalls. It is the
responsibility of the Peers to send messages with a frequency
sufficient to maintain the necessary state in these NATs and
firewalls and thus keep the connection alive. Keepalives are a
mandatory component of ICE (see Section 10 of [RFC5245]) and no
further operations are required. Applications that want to assure
maintenance of sessions individually need to follow regular SIP
means. Accordingly, a SIP Peer MAY apply keep-alive techniques in
agreement with its transport binding as defined in Section 3.5 of
[RFC5626].

6. Using GRUUs

Globally Routable User Agent URIs (GRUUs) [RFC5627] have been
designed to allow direct routing to a specific UA instance without
the need for dereferencing by a domain-specific SIP proxy function.
The concept is transferred to RELOAD overlays as follows. GRUUs in
RELOAD are constructed by embedding a base64-encoded destination list
in the "gr" URI parameter of the GRUU. The base64 encoding is done
with the alphabet specified in Table 1 of [RFC4648] with the
exception that "~" is used in place of "=".

Example of a RELOAD GRUU:
[email protected];gr=MDEyMzQ1Njc4OTAxMjM0NTY3ODk~

GRUUs do not require storing data in the Overlay Instance. Rather,
when a Peer needs to route a message to a GRUU in the same P2P
overlay, it simply uses the destination list and connects to that
Peer. Because a GRUU contains a destination list, it can have the
same contents as a destination list stored elsewhere in the resource
dictionary.

Anonymous GRUUs [RFC5767] are constructed analogously, but require
either that the enrollment server issues a different Node-ID for each
anonymous GRUU required, or that a destination list be used that
includes a Peer that compresses the destination list to stop the
Node-ID from being revealed.

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RFC 7904 RELOAD SIP Usage October 2016

7. SIP-REGISTRATION Kind Definition

This section defines the SIP-REGISTRATION Kind.

Name: SIP-REGISTRATION

Kind IDs: The Resource Name for the SIP-REGISTRATION Kind-ID is the
AOR of the user as specified in Section 2. The data stored is a
SipRegistration, which can contain either another URI or a
destination list to the Peer that is acting for the user.

Data Model: The data model for the SIP-REGISTRATION Kind-ID is a
dictionary. The dictionary key is the Node-ID of the Storing
Peer. This allows each Peer (presumably corresponding to a single
device) to store a single route mapping.

Access Control: USER-NODE-MATCH. Note that this matches the SIP AOR
against the rfc822Name in the X.509 v3 certificate. The
rfc822Name does not include the scheme so that the "sip:" prefix
needs to be removed from the SIP AOR before matching. Escaped
characters ('%' encoding) in the SIP AOR also need to be decoded
prior to matching (see [RFC3986]).

Data stored under the SIP-REGISTRATION Kind is of type
SipRegistration, containing one of two data types:

sip_registration_uri

A URI that the user can be reached at.

sip_registration_route

A destination list that can be used to reach the user's Peer.

8. Security Considerations

8.1. RELOAD-Specific Issues

This Usage for RELOAD does not define new protocol elements or
operations. Hence, no new threats arrive from message exchanges in
RELOAD.

This document introduces an AOR domain restriction function that must
be compared against the registration attempt by the Storing Peer. A
misconfigured or malicious Peer could cause frequent rejects of
illegitimate storing requests. However, domain name control relies
on a lightweight pattern matching and can be processed prior to

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RFC 7904 RELOAD SIP Usage October 2016

validating certificates. Hence, no extra burden is introduced for
RELOAD peers beyond loads already present in the base protocol.

8.2. SIP-Specific Issues

8.2.1. Fork Explosion

Because SIP includes a forking capability (the ability to retarget to
multiple recipients), fork bombs (i.e., attacks using SIP forking to
amplify the effect on the intended victims) are a potential DoS
concern. However, in the SIP Usage of RELOAD, fork bombs are a much
lower concern than in a conventional SIP Proxy infrastructure,
because the calling party is involved in each retargeting event. It
can therefore directly measure the number of forks and throttle at
some reasonable number.

8.2.2. Malicious Retargeting

To launch a DoS attack, the owner of a popular AOR could retarget all
calls to the victim. This attack is common to SIP and is difficult
to ameliorate without requiring the target of a SIP registration to
authorize all stores. The overhead of that requirement would be
excessive and, in addition, there are good use cases for retargeting
to a Peer without its explicit cooperation.

8.2.3. Misuse of AORs

A RELOAD overlay and enrollment service that liberally accepts
registrations for AORs of domain names unrelated to the overlay
instance and without further authorization could store presence state
for AORs without the consent of the owner of the AOR. An attacker
could hijack names, register a bogus presence, and attract calls
dedicated to a victim that resides within or outside the Overlay
Instance.

A hijacking of AORs can be mitigated by restricting the name spaces
admissible in the Overlay Instance, or by additional verification
actions of the enrollment service. To prevent an (exclusive) routing
to a bogus registration, a caller can in addition query the DNS (or
other discovery services at hand), search for an alternative presence
of the callee in another overlay or a SIP infrastructure using
[RFC3263] for name resolution.

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RFC 7904 RELOAD SIP Usage October 2016

8.2.4. Privacy Issues

All RELOAD SIP registration data is visible to all nodes in the
overlay. Location privacy can be gained from using anonymous GRUUs.
Methods of providing anonymity or deploying pseudonyms exist, but are
beyond the scope of this document.

9. IANA Considerations

9.1. Data Kind-ID

IANA has registered the following code point in the "RELOAD Data
Kind-ID" Registry (cf., [RFC6940]) to represent the SIP-REGISTRATION
Kind, as described in Section 7.

+---------------------+------------+-----------+
| Kind | Kind-ID | Reference |
+---------------------+------------+-----------+
| SIP-REGISTRATION | 0x1 | RFC 7904 |
+---------------------+------------+-----------+

9.2. XML Namespace Registration

This document registers the following URI for the config XML
namespace in the IETF XML registry defined in [RFC3688]:

URI: urn:ietf:params:xml:ns:p2p:config-base:sip

Registrant Contact: The IESG

XML: N/A; the requested URI is an XML namespace

10. References

10.1. Normative References

[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>.

[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>.

Jennings, et al. Standards Track [Page 16]

RFC 7904 RELOAD SIP Usage October 2016

[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.

[RFC2533] Klyne, G., "A Syntax for Describing Media Feature Sets",
RFC 2533, DOI 10.17487/RFC2533, March 1999,
<http://www.rfc-editor.org/info/rfc2533>.

[RFC2738] Klyne, G., "Corrections to "A Syntax for Describing Media
Feature Sets"", RFC 2738, DOI 10.17487/RFC2738, December
1999, <http://www.rfc-editor.org/info/rfc2738>.

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.

[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840,
DOI 10.17487/RFC3840, August 2004,
<http://www.rfc-editor.org/info/rfc3840>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.

[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>.

[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.

[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.

Jennings, et al. Standards Track [Page 17]

RFC 7904 RELOAD SIP Usage October 2016

[RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
"Managing Client-Initiated Connections in the Session
Initiation Protocol (SIP)", RFC 5626,
DOI 10.17487/RFC5626, October 2009,
<http://www.rfc-editor.org/info/rfc5626>.

[RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent URIs (GRUUs) in the Session Initiation Protocol
(SIP)", RFC 5627, DOI 10.17487/RFC5627, October 2009,
<http://www.rfc-editor.org/info/rfc5627>.

[IEEE-Posix]
IEEE, "International Standard - Information technology
Portable Operating System Interface (POSIX) Base
Specifications, Issue 7", ISO/IEC/IEEE 9945:2009,
DOI 10.1109/IEEESTD.2009.5393893, September 2009.

10.2. Informative References

[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
DOI 10.17487/RFC3263, June 2002,
<http://www.rfc-editor.org/info/rfc3263>.

[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, DOI 10.17487/RFC3966, December 2004,
<http://www.rfc-editor.org/info/rfc3966>.

[RFC7890] Bryan, D., Matthews, P., Shim, E., Willis, D., and S.
Dawkins, "Concepts and Terminology for Peer-to-Peer SIP
(P2PSIP)", RFC 7890, DOI 10.17487/RFC7890, June 2016,
<http://www.rfc-editor.org/info/rfc7890>.

[RFC5767] Munakata, M., Schubert, S., and T. Ohba, "User-Agent-
Driven Privacy Mechanism for SIP", RFC 5767,
DOI 10.17487/RFC5767, April 2010,
<http://www.rfc-editor.org/info/rfc5767>.

[SHARE] Knauf, A., Schmidt, T., Hege, G., and M. Waehlisch, "A
Usage for Shared Resources in RELOAD (ShaRe)", Work in
Progress, draft-ietf-p2psip-share-08, March 2016.

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RFC 7904 RELOAD SIP Usage October 2016

Appendix A. Third-Party Registration

Non-peer-to-peer SIP defines third-party registration (e.g., an
assistant acting for a manager or a changing set of users registering
under a role-based AOR) in Section 10.2 of [RFC3261]. This is a
REGISTER that uses the URI of the third party in its From header and
cannot be translated directly into a P2PSIP registration because only
the owner of the certificate can store a SIP-REGISTRATION in a RELOAD
overlay.

Third-party registration can be implemented by using the extended
access control mechanism USER-CHAIN-ACL defined in [SHARE]. Creating
a new Kind "SIP-3P-REGISTRATION" that is ruled by USER-CHAIN-ACL
allows the owner of the certificate to delegate the right for
registration to individual third parties. This way, the SIP third-
party registration functionality can be regained without weakening
the security controls of RELOAD.

Acknowledgments

This document was generated in parts from initial drafts and
discussions in the early specification phase of the P2PSIP base
protocol. We gratefully acknowledge the significant contributions
made by (in alphabetical order) David A. Bryan, James Deverick,
Marcin Matuszewski, Jonathan Rosenberg, and Marcia Zangrilli.

Additional thanks go to all those who helped with ideas, discussions,
and reviews, in particular (in alphabetical order) Roland Bless,
Michael Chen, Alissa Cooper, Marc Petit-Huguenin, Brian Rosen, Meral
Shirazipour, and Matthias Waehlisch.

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RFC 7904 RELOAD SIP Usage October 2016

Authors' Addresses

Cullen Jennings
Cisco
170 West Tasman Drive
MS: SJC-21/2
San Jose, CA 95134
United States of America
Phone: +1 408 421-9990
Email: [email protected]

Bruce B. Lowekamp
Skype
Palo Alto, CA
United States of America
Email: [email protected]

Eric Rescorla
RTFM, Inc.
2064 Edgewood Drive
Palo Alto, CA 94303
United States of America
Phone: +1 650 678 2350
Email: [email protected]

Salman A. Baset
IBM T. J. Watson Research Center
1101 Kitchawan Road
Yorktown Heights, NY 10598
United States of America
Email: [email protected]

Henning Schulzrinne
Columbia University
1214 Amsterdam Avenue
New York, NY 10027
United States of America
Email: [email protected]

Thomas C. Schmidt (editor)
HAW Hamburg
Berliner Tor 7
Hamburg 20099
Germany
Email: [email protected]

Jennings, et al. Standards Track [Page 20]