Session Description Protocol (SDP) Source Filters
RFC 4570

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Network Working Group                                           B. Quinn
Request for Comments: 4570                                 BoxnArrow.com
Category: Standards Track                                   R. Finlayson
                                                     Live Networks, Inc.
                                                               July 2006

           Session Description Protocol (SDP) Source Filters

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes how to adapt the Session Description Protocol
   (SDP) to express one or more source addresses as a source filter for
   one or more destination "connection" addresses.  It defines the
   syntax and semantics for an SDP "source-filter" attribute that may
   reference either IPv4 or IPv6 address(es) as either an inclusive or
   exclusive source list for either multicast or unicast destinations.
   In particular, an inclusive source-filter can be used to specify a
   Source-Specific Multicast (SSM) session.

1.  Introduction

   The Session Description Protocol [SDP] provides a general purpose
   format for describing multimedia sessions in announcements or
   invitations.  SDP uses an entirely textual data format (the US-ASCII
   subset of [UTF-8]) to maximize portability among transports.  SDP
   does not define a protocol, but only the syntax to describe a
   multimedia session with sufficient information to discover and
   participate in that session.  Session descriptions may be sent using
   any number of existing application protocols for transport (e.g.,
   Session Announcement Protocol (SAP), SIP, Real Time Streaming
   Protocol (RTSP), email, and HTTP).

   Typically, session descriptions reference an IP multicast address for
   the "connection-address" (destination), though unicast addresses or
   fully qualified domain names (FQDNs) MAY also be used.  The "source-

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RFC 4570                   SDP Source Filters                  July 2006

   filter" attribute defined in this document qualifies the session
   traffic by identifying the address (or FQDN) of legitimate sources
   (senders).  The intent is for receivers to use the source and
   destination address pair(s) to filter traffic, so that applications
   receive only legitimate session traffic.

   Receiver applications are expected to use the SDP source-filter
   information to identify traffic from legitimate senders, and discard
   traffic from illegitimate senders.  Applications and hosts may also
   share the source-filter information with network elements (e.g., with
   routers using [IGMPv3]) so they can potentially perform the traffic
   filtering operation further "upstream," closer to the source(s).

   The "source-filter" attribute can appear at the session level and/or
   the media level.

1.1.  Motivation

   The purpose of a source-filter is to help protect receivers from
   traffic sent from illegitimate source addresses.  Filtering traffic
   can help to preserve content integrity and protect against Denial of
   Service (DoS) attacks.

   For multicast destination addresses, receiver applications MAY apply
   source-filters using the Multicast Source Filter APIs [MSF-API].
   Hosts are likely to implement these APIs using protocol mechanisms to
   convey the source filters to local multicast routers.  Other
   "upstream" multicast routers MAY apply the filters and thereby
   provide more explicit multicast group management and efficient
   utilization of network resources.  The protocol mechanisms to enable
   these operations are beyond the scope of this document, but their
   potential provided motivation for SDP source-filters.

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 [REQMNT].

3.  The "source-filter" Attribute

   The SDP source-filter attribute does not change any existing SDP
   syntax or semantics, but defines a format for additional session
   description information.  Specifically, source-filter syntax can
   prescribe one or more unicast addresses as either legitimate or
   illegitimate sources for any (or all) SDP session description
   "connection-address" field values.

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RFC 4570                   SDP Source Filters                  July 2006

   Note that the unicast source addresses specified by this attribute