draft-ietf-mmusic-sdp-srcfilter-02.txt   draft-ietf-mmusic-sdp-srcfilter-03.txt 
Internet-Draft Bob Quinn INTERNET-DRAFT Bob Quinn
Celox Networks; Celox Networks;
Ross Finlayson Ross Finlayson
LIVE.COM LIVE.COM
Expires 24 April 2003 24 October 2002 Expires 15 August 2003 15 February 2003
SDP Source-Filters Session Description Protocol (SDP) Source Filters
<draft-ietf-mmusic-sdp-srcfilter-02.txt> <draft-ietf-mmusic-sdp-srcfilter-03.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is subject to
provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
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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].
Abstract Abstract
This document describes how to adapt the Session Description Protocol This document describes how to adapt the Session Description Protocol
(SDP) to express one or more source addresses as a source filter for (SDP) to express one or more source addresses as a source filter for
one or more destination "connection" addresses. It defines the syntax one or more destination "connection" addresses. It defines the syntax
and semantics for an SDP "source-filter" attribute that may reference and semantics for an SDP "source-filter" attribute that may reference
either IPv4 or IPv6 address(es) as either an inclusive or exclusive either IPv4 or IPv6 address(es) as either an inclusive or exclusive
source list for either multicast or unicast destinations. In particular, source list for either multicast or unicast destinations. In particular,
an inclusive source-filter can be used to specify a Source-Specific an inclusive source-filter can be used to specify a Source-Specific
Multicast ("SSM") session. Multicast (SSM) session.
Receiver applications are expected use the SDP source-filter Receiver applications are expected use the SDP source-filter
information to identify traffic from legitimate senders and discard information to identify traffic from legitimate senders and discard
traffic from illegitimate senders. Applications and hosts may also traffic from illegitimate senders. Applications and hosts may also
share the source-filter information with network elements (e.g., with share the source-filter information with network elements (e.g., with
routers using IGMPv3) so they can potentially perform the traffic routers using IGMPv3) so they can potentially perform the traffic
filtering operation further "upstream," closer to the source(s). filtering operation further "upstream," closer to the source(s).
1 Introduction 1 Introduction
skipping to change at line 62 skipping to change at line 66
invitations. SDP uses an entirely textual data format (the US-ASCII invitations. SDP uses an entirely textual data format (the US-ASCII
subset of [UTF-8]) to maximize portability among transports. SDP does subset of [UTF-8]) to maximize portability among transports. SDP does
not define a protocol, but only the syntax to describe a multimedia not define a protocol, but only the syntax to describe a multimedia
session with sufficient information to discover and participate in that session with sufficient information to discover and participate in that
session. Session descriptions may be sent using any number of existing session. Session descriptions may be sent using any number of existing
application protocols for transport (e.g., SAP, SIP, RTSP, email, HTTP, application protocols for transport (e.g., SAP, SIP, RTSP, email, HTTP,
etc.). etc.).
Typically, session descriptions reference an IP multicast address for Typically, session descriptions reference an IP multicast address for
the "connection-address" (destination), though unicast addresses or the "connection-address" (destination), though unicast addresses or
fully qualified domain names (FQDNs) may also be used. The "source- fully qualified domain names (FQDNs) MAY also be used. The "source-
filter" attribute that this document defines qualifies the session filter" attribute defined in this document defines qualifies the session
traffic by identifying the address (or FQDN) of legitimate source(s) traffic by identifying the address (or FQDN) of legitimate source(s)
(senders). The intent is for receivers to use the source and (senders). The intent is for receivers to use the source and
destination address pair(s) to filter traffic, so applications receive destination address pair(s) to filter traffic, so applications receive
only legitimate session traffic. only legitimate session traffic.
1.1 Motivation 1.1 Motivation
The purpose of a source-filter is to help protect receivers from The purpose of a source-filter is to help protect receivers from
traffic sent from illegitimate source addresses. Filtering traffic can traffic sent from illegitimate source addresses. Filtering traffic can
help to preserve content integrity and protect against denial of help to preserve content integrity and protect against denial of
service (DoS) attacks. service (DoS) attacks.
For multicast destination addresses, receiver applications may apply For multicast destination addresses, receiver applications MAY apply
source-filters using the Multicast Source Filter APIs [MSF API]. Hosts source-filters using the Multicast Source Filter APIs [MSF API]. Hosts
are likely to implement these APIs using protocol mechanisms to convey are likely to implement these APIs using protocol mechanisms to convey
the source filters to local multicast routers. Other "upstream" the source filters to local multicast routers. Other "upstream"
multicast routers may apply the filters and thereby provide more multicast routers MAY apply the filters and thereby provide more
explicit multicast group management and efficient utilization of explicit multicast group management and efficient utilization of
network resources. The protocol mechanisms to enable these operations network resources. The protocol mechanisms to enable these operations
are beyond the scope of this document, but their potential provided are beyond the scope of this document, but their potential provided
motivation for SDP source-filters. motivation for SDP source-filters.
2 Source-filter Attribute 2 The "source-filter" Attribute
The SDP source-filter attribute does not change any existing SDP syntax The SDP source-filter attribute does not change any existing SDP syntax
or semantics, but defines a format for additional session description or semantics, but defines a format for additional session description
information. Specifically, source-filter syntax can prescribe one or information. Specifically, source-filter syntax can prescribe one or
more unicast addresses as either legitimate or illegitimate sources for more unicast addresses as either legitimate or illegitimate sources for
any (or all) SDP session description "connection-address" field values. any (or all) SDP session description "connection-address" field values.
The source-filter attribute is comprised of two parts: The source-filter attribute has the following syntax:
a=<filter-mode>:<filter-spec> a=source-filter: <filter-mode> <filter-spec>
The <filter-mode> is either "incl" or "excl" (for inclusion or The <filter-mode> is either "incl" or "excl" (for inclusion or
exclusion, respectively), and the <filter-spec> has four sub- exclusion, respectively). The <filter-spec> has four sub-components:
components:
<nettype> <address-types> <dest-address> <src-list> <nettype> <address-types> <dest-address> <src-list>
A <filter-mode> of "incl" means that an incoming packet is accepted
only if its source address is in the set specified by <src-list>.
A <filter-mode> of "excl" means that an incoming packet is rejected
if its source address is in the set specified by <src-list>.
The first sub-field <nettype> indicates the network type, since SDP is The first sub-field <nettype> indicates the network type, since SDP is
protocol independent. This document is most relevant to the value protocol independent. This document is most relevant to the value
"IN", which designates the Internet Protocol. "IN", which designates the Internet Protocol.
Second sub-field <address-types> identifies the address family and for Second sub-field <address-types> identifies the address family and for
the purpose of this document may be either <addrtype> values "IP4" or the purpose of this document may be either <addrtype> values "IP4" or
"IP6". Alternately, when <dest-address> is an FQDN, the value may be "IP6". Alternately, when <dest-address> is an FQDN, the value MAY be
"*" to apply to both address types, since either address may be "*" to apply to both address types, since either address can be
returned from a DNS lookup. returned from a DNS lookup.
The third sub-field <dest-address> is the destination address, which The third sub-field <dest-address> is the destination address, which
must correspond to one or more of the session's "connection-address" MUST correspond to one or more of the session's "connection-address"
field values. It may be either a unicast or multicast address, an FQDN field values. It may be either a unicast or multicast address, an FQDN
(fully-qualified domain name), or the "*" wildcard to match any/all of (fully-qualified domain name), or the "*" wildcard to match any/all of
the session's "connection-address" values. the session's "connection-address" values.
And the fourth sub-field <src-list> is the list of source The fourth sub-field <src-list> is the list of source
hosts/interfaces in the source-filter, and consists of one or more hosts/interfaces in the source-filter, and consists of one or more
unicast addresses or FQDNs, separated by space characters. unicast addresses or FQDNs, separated by space characters.
The format and content of these semantic elements are derived from and The format and content of these semantic elements are derived from and
compatible with those defined in [SDP]. For more detail, see Appendix compatible with those defined in [SDP]. For more detail, see Appendix
A in this document. A in this document.
2.1 Processing Rules 2.1 Processing Rules
There are a number of details to consider when parsing the SDP source- There are a number of details to consider when parsing the SDP source-
filter syntax. filter syntax.
The <dest-address> value in a <source-filter> attribute must correspond The <dest-address> value in a "source-filter" attribute MUST correspond
to an existing <connection-field> value in the session description. to an existing <connection-field> value in the session description.
The only exception to this is when a "*" wildcard is used to indicate The only exception to this is when a "*" wildcard is used to indicate
that the source-filter applies to all <connection-field> values. that the source-filter applies to all <connection-field> values.
When the <dest-address> value is a multicast address, the field value When the <dest-address> value is a multicast address, the field value
should NOT include the sub-fields <ttl> and <number of addresses> from MUST NOT include the sub-fields <ttl> and <number of addresses> from
the <connection-address> value. The <number of addresses> is implied, the <connection-address> value. The <number of addresses> is implied,
and all unicast addresses in the <src-list> are valid sources for any and all unicast addresses in the <src-list> are valid sources for any
of the multicast addresses in the address series implied by the <number of the multicast addresses in the address series implied by the <number
of addresses>. See section 2.2.4 for an example. of addresses>.
When the <addrtype> value is the "*" wildcard, the <dest-address> must When the <addrtype> value is the "*" wildcard, the <dest-address> MUST
be either an FQDN or "*" (i.e., it cannot be either an IPv4 or IPv6 be either an FQDN or "*" (i.e., it MUST NOT be an IPv4 or IPv6
address). See section 2.2.6 for an example. address). See section 2.2.5 for an example.
As has always been the case, the default behavior when a source-filter As has always been the case, the default behavior when a source-filter
attribute is not provided in a session description is that all traffic attribute is not provided in a session description is that all traffic
sent to the specified <connection-address> value should be accepted sent to the specified <connection-address> value should be accepted
(i.e., from any source address). The source-filter grammar does not (i.e., from any source address). The source-filter grammar does not
include syntax to express either "exclude none" or "include all." include syntax to express either "exclude none" or "include all."
Like the standard <connection-field> described in [SDP], the location Like the standard <connection-field> described in [SDP], the location
of the <source-filter> attribute determines whether it applies to the of the "source-filter" attribute determines whether it applies to the
entire session or only to a specific media (i.e., "session-level" or entire session or only to a specific medium (i.e., "session-level" or
"media-level"). A media-level source-filter will always override a "media-level"). A media-level source-filter will always completely
session-level source-filter. override a session-level source-filter.
A <source-filter> need not be located at the same hierarchy level as A "source-filter" need not be located at the same hierarchy level as
its corresponding <connection-field>. Hence, a media-level <source- its corresponding <connection-field>. So, a media-level <source-
filter> can reference a session-level <connection-field> value, and a filter> can reference a session-level <connection-field> value, and a
session-level <source-filter> may be applied to all matching media- session-level "source-filter" can be applied to all matching media-
level <connection-field> values. See section 2.2.3 for an example. level <connection-field> values. See section 2.2.3 for an example.
Only one source filter attribute entry may be defined for each A SDP description MUST NOT contain more than one session-level
<connection address> value at either session-level or media-level. If "source-filter" attribute, nor more than one media-level
more than one is provided, only the first <source-filter> attribute to "source-filter" attribute for the same medium.
appear is used (and other <source-filter> entries MUST be ignored).
There is no specified limit to the number of entries allowed in the There is no specified limit to the number of entries allowed in the
<src-list>, however there are practical limits that should be <src-list>, however there are practical limits that should be
considered. For example, depending on the transport to be used for the considered. For example, depending on the transport to be used for the
session description, there may be a limit to the total size of the session description, there may be a limit to the total size of the
session description (e.g., as determined by the maximum payload in a session description (e.g., as determined by the maximum payload in a
single datagram). Also, when the source-filter is applied to control single datagram). Also, when the source-filter is applied to control
protocols, there may be a limit to the number of source addresses that protocols, there may be a limit to the number of source addresses that
can be sent. These limits are outside the scope of this document, but can be sent. These limits are outside the scope of this document, but
should be considered when defining source-filter values for SDP. should be considered when defining source-filter values for SDP.
skipping to change at line 192 skipping to change at line 199
2.2 Examples 2.2 Examples
Here are a number of examples that illustrate how to use the source- Here are a number of examples that illustrate how to use the source-
filter attribute in some common scenarios. We use the following filter attribute in some common scenarios. We use the following
session description components as the starting point for the examples session description components as the starting point for the examples
to follow. For each example, we show the source filter with additional to follow. For each example, we show the source filter with additional
relevant information, and provide a brief explanation. relevant information, and provide a brief explanation.
<session-description> = <session-description> =
v=0 v=0
o=The King <Elvis@ipmulticast.com> o=The King <Elvis@example.com>
s=Elvis Impersonation s=Elvis Impersonation
i=All Elvis, all the time i=All Elvis, all the time
u=http://www.ipmulticast.com/ElvisLive/ u=http://www.example.com/ElvisLive/
t=0 0 t=0 0
a=recvonly a=recvonly
<media-description 1> = <media-description 1> =
m=audio 54320 RTP/AVP 0 m=audio 54320 RTP/AVP 0
<media-description 2> = <media-description 2> =
m=video 54322 RTP/AVP 34 m=video 54322 RTP/AVP 34
2.2.1 Source-Specific Multicast Example 2.2.1 Source-Specific Multicast Example
Multicast addresses in the Source-Specific Multicast [SSM] range Multicast addresses in the Source-Specific Multicast [SSM] range
require a single unicast sender address for each multicast destination, require a single unicast sender address for each multicast destination,
so the source-filter specification provides a natural fit. In this so the source-filter specification provides a natural fit. In this
example, a session member should receive only traffic sent from example, a session member should receive only traffic sent from
192.168.9.10 to the multicast session address 232.3.4.5. 192.168.9.10 to the multicast session address 232.3.4.5.
<session-description> <session-description>
c=IN IP4 232.3.4.5/127 c=IN IP4 232.3.4.5/127
a=incl:IN IP4 232.3.4.5 192.168.9.10 a=source-filter: incl IN IP4 232.3.4.5 192.168.9.10
<media-description 1> <media-description 1>
This source filter example uses an inclusion list with a single This source filter example uses an inclusion list with a single
multicast "connection-address" as the destination and single unicast multicast "connection-address" as the destination and single unicast
address as the source. Note that the value of the connection-address address as the source. Note that the value of the connection-address
matches the value specified in the connection-field. matches the value specified in the connection-field.
Also note that since the connection-field is located in the session- Also note that since the connection-field is located in the session-
description section, the source-filter applies to all media. description section, the source-filter applies to all media.
Furthermore, if the SDP description specifies a RTP session Furthermore, if the SDP description specifies a RTP session
(e.g., it's "m=" line(s) specify "RTP/AVP" as the transport protocol), (e.g., its "m=" line(s) specify "RTP/AVP" as the transport protocol),
then the "a=incl:" specification will apply not only to RTP packets, then the "incl" specification will apply not only to RTP packets,
but also to any RTCP packets that are sent to the specified multicast but also to any RTCP packets that are sent to the specified multicast
address. This means that, as a side effect of the "a=incl:" address. This means that, as a side effect of the "incl"
specification, the only possible multicast RTCP packets will be specification, the only possible multicast RTCP packets will be
"Sender Report" (SR) packets sent from the specified source address. "Sender Report" (SR) packets sent from the specified source address.
Because of this, a SDP description for a Source-Specific Multicast Because of this, a SDP description for a Source-Specific Multicast
(SSM) session SHOULD also include a (SSM) RTP session SHOULD also include a
a=rtcp:unicast ... a=rtcp:unicast ...
attribute, as described in [RTCP-SSM]. This specifies that RTCP attribute, as described in [RTCP-SSM]. This specifies that RTCP
"Reception Report" (RR) packets are to be sent back via unicast. "Reception Report" (RR) packets are to be sent back via unicast.
2.2.2 Unicast Exclusion Example 2.2.2 Unicast Exclusion Example
Typically, an SDP session <connection-address> value is a multicast Typically, an SDP session <connection-address> value is a multicast
address, although it is also possible to use either a unicast address, although it is also possible to use either a unicast
address or FQDN. This example illustrates a scenario whereby a session address or FQDN. This example illustrates a scenario whereby a session
description indicates the unicast source address 192.168.9.10 in an description indicates the unicast source address 192.168.9.10 in an
exclusion filter. In effect, this sample source-filter says, "host exclusion filter. In effect, this sample source-filter says, "host
192.168.10.11 destination should accept traffic from any sender 192.168.10.11 destination should accept traffic from any sender
*except* 192.168.9.10." *except* 192.168.9.10."
<session-description> <session-description>
c=IN IP4 192.168.10.11 c=IN IP4 192.168.10.11
a=excl:IN IP4 192.168.10.11 192.168.9.10 a=source-filter: excl IN IP4 192.168.10.11 192.168.9.10
<media-description 1> <media-description 1>
2.2.3 Multiple Session Address Example 2.2.3 Multiple Session Address Example
This source-filter example uses the wildcard "*" value for <dest-addr> This source-filter example uses the wildcard "*" value for <dest-addr>
to correspond to any/all <connection-address> values. Hence, the only to correspond to any/all <connection-address> values. Hence, the only
legitimate source for traffic sent to either 232.2.2.2 or 232.4.4.4 legitimate source for traffic sent to either 232.2.2.2 or 232.4.4.4
multicast addresses is 192.168.9.10. Traffic sent from any other multicast addresses is 192.168.9.10. Traffic sent from any other
unicast source address should be discarded by the receiver. unicast source address should be discarded by the receiver.
<session-description> <session-description>
a=incl:IN IP4 * 192.168.9.10 a=source-filter: incl IN IP4 * 192.168.9.10
<media-description 1> <media-description 1>
c=IN IP4 232.2.2.2/127 c=IN IP4 232.2.2.2/127
<media-description 2> <media-description 2>
c=IN IP4 232.4.4.4/63 c=IN IP4 232.4.4.4/63
2.2.4 Multiple Source and Destination Example 2.2.4 IPv6 Multicast Source-Filter Example
The source-filter in this example specifies a legitimate source address
for each of three multicast addresses in a series. Specifically,
1.1.1.1 is the legitimate source for 232.3.4.5, 2.2.2.2 is the
legitimate source for 232.3.4.6, and 3.3.3.3 is the legitimate source
for 232.3.4.7. Traffic sent from any other source addresses should be
discarded.
<session-description>
c=IN IP4 232.3.4.5/127/3
a=incl:IN IP4 232.3.4.5 1.1.1.1 2.2.2.2 3.3.3.3
<media-description 1>
2.2.5 IPv6 Multicast Source-Filter Example
This simple example defines a single session-level source-filter that This simple example defines a single session-level source-filter that
references a single IPv6 multicast destination and source pair. The IP references a single IPv6 multicast destination and source pair. The IP
multicast traffic sent to FFOE::11A is only valid from the unicast multicast traffic sent to FFOE::11A is valid only from the unicast
source address 2001:210:1:2:240:96FF:FE25:8EC9 source address 2001:210:1:2:240:96FF:FE25:8EC9
<session-description> <session-description>
c=IN IP6 FF0E::11A/127 c=IN IP6 FF0E::11A/127
a=incl:IN IP6 FF0E::11A 2001:210:1:2:240:96FF:FE25:8EC9 a=source-filter incl IN IP6 FF0E::11A 2001:210:1:2:240:96FF:FE25:8EC9
<media-description 1> <media-description 1>
2.2.6 IPv4 and IPv6 FQDN Example 2.2.5 IPv4 and IPv6 FQDN Example
This example illustrates use of the <addrtype> wildcard along with This example illustrates use of the <addrtype> "*" wildcard, along with
multicast and source FQDNs that may resolve to either an IPv6 or IPv4 multicast and source FQDNs that may resolve to either an IPv6 or IPv4
address, or both. Although typically both the multicast and source address, or both. Although typically both the multicast and source
addresses will be the same (either both IPv4 or IPv6), using the addresses will be the same (either both IPv4 or IPv6), using the
wildcard for addrtype in the source filter allows asymmetry between the wildcard for addrtype in the source filter allows asymmetry between the
two addresses (so an IPv4 source address may be used with an IPv6 two addresses (so an IPv4 source address may be used with an IPv6
multicast address). multicast address).
<session-description> <session-description>
c=IN IP4 Channel-1.ipmulticast.com/127 c=IN IP4 channel-1.example.com/127
c=IN IP6 Channel-1.ipmulticast.com/127 c=IN IP6 channel-1.example.com/127
a=incl:IN * Channel-1.ipmulticast.com Src-1.ipmulticast.com a=source-filter: incl IN * channel-1.example.com src-1.example.com
<media-description 1> <media-description 1>
3 Interoperability Issues 3 Interoperability Issues
Defining a list of legitimate sources for a multicast destination Defining a list of legitimate sources for a multicast destination
address represents a departure from the Any-Source Multicast address represents a departure from the Any-Source Multicast
(ASM) model, as originally described in [IGMPv1]. The ASM model (ASM) model, as originally described in [IGMPv1]. The ASM model
supports anonymous senders, and all types of multicast applications supports anonymous senders, and all types of multicast applications
(e.g., many-to-many). Use of a source-filter excludes some (unknown or (e.g., many-to-many). Use of a source-filter excludes some (unknown or
undesirable) senders, which lends itself more to one-to-many or few-to- undesirable) senders, which lends itself more to one-to-many or few-to-
few type multicast applications. few type multicast applications.
Although these two models have contrasting operational characteristics Although these two models have contrasting operational characteristics
and requirements, they can coexist on the same network using the same and requirements, they can coexist on the same network using the same
protocols. Use of source-filters do not corrupt the ASM semantics but protocols. Use of source-filters do not corrupt the ASM semantics but
provide more control for receivers, at their discretion. provide more control for receivers, at their discretion.
4 Security Considerations 4 Normative References
See [SDP] for security other considerations specific to the Session [ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax
Specifications: ABNF," RFC 2234, November 1997
[REQMNT] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," BCP 14, RFC 2119, March 1997.
[RTCP-SSM] J. Chesterfield, et al.
"RTCP Extensions for Single-Source Multicast Sessions
with Unicast Feedback," Work in progress, November 2002
[SDP] M. Handley, V. Jacobson, "SDP: Session Description
Protocol," RFC 2327, April 1998
[UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
and ISO 10646," RFC 2044, October 1996
5 Informative References
[CA-96.21] CERT Advisory CA-96.21, "TCP SYN Flooding and IP
Spoofing Attacks," September 1996
[IGMPv1] S. Deering, "Host Extensions for IP Multicasting," RFC
1112 (STD 5), August 1989
[IGMPv3] B. Cain et al. "Internet Group Management Protocol,
Version 3,", Work in progress, May 2002.
[MSF API] D. Thaler, B. Fenner, B. Quinn, "Socket Interface
Extensions for Multicast Source Filters,"
Work in progress, July 2002.
[SSM] Bhattacharyya, S. et al., "An Overview of Source-Specific
Multicast (SSM)", Work in progress, October 2002.
6 Security Considerations
See [SDP] for security considerations specific to the Session
Description Protocol in general. The central issue relevant to using Description Protocol in general. The central issue relevant to using
unicast source address filters is the question of address authenticity. unicast source address filters is the question of address authenticity.
Using the source IP address for authentication is weak, since addresses Using the source IP address for authentication is weak, since addresses
are often dynamically assigned and it is possible for a sender to are often dynamically assigned and it is possible for a sender to
"spoof" its source address (use one other than their own) in datagrams "spoof" its source address (use one other than its own) in datagrams
they send. Proper router configuration can reduce the likelihood of it sends. Proper router configuration can reduce the likelihood of
"spoofed" source addresses being sent to or from a network, however. "spoofed" source addresses being sent to or from a network, however.
Specifically, border routers are encouraged to filter traffic so Specifically, border routers are encouraged to filter traffic so
datagrams with invalid source addresses are not forwarded (e.g., datagrams with invalid source addresses are not forwarded (e.g.,
routers drop datagrams if the source address is non-local) [CA-96.21]. routers drop datagrams if the source address is non-local) [CA-96.21].
Despite the weaknesses of source address-based filtering, this
mechanism provides more security than is currently available with
respect to source authentication of IP Multicast senders.
Use of FQDNs for either <dest-address> or <src-list> values provides a Use of FQDNs for either <dest-address> or <src-list> values provides a
layer of indirection that provides great flexibility. However, it also layer of indirection that provides great flexibility. However, it also
exposes the source-filter to any security inadequacies that the DNS exposes the source-filter to any security inadequacies that the DNS
system may have (if any). If unsecured, it is conceivable that the DNS system may have (if any). If unsecured, it is conceivable that the DNS
server could return illegitimate addresses. server could return illegitimate addresses.
5 IANA Considerations 7 IANA Considerations
As recommended by [SDP] (in Appendix B), the new source-filter As recommended by [SDP] (in Appendix B), the new "source-filter"
attribute described in this document should be registered with IANA. attribute described in this document should be registered with IANA.
Acknowledgements 8 Acknowledgements
The author would like to thank Dave Thaler and Mark Handley, whose The authors would like to thank Dave Thaler and Mark Handley, whose
input provided much of the substance of this document. input provided much of the substance of this document. Also,
Magnus Westerlund provided valuable feedback during editing.
9 Authors' Addresses
Bob Quinn
Celox Networks
2 Park Central Drive
Southborough, MA 01772
phone: 508-305-7000
email: bquinn (at) celoxnetworks.com
Ross Finlayson
Live Networks, Inc. (LIVE.COM)
650 Castro St., suite 120-196
Mountain View, CA 94041
email: finlayson (at) live.com
Appendix A: Source-Filter Attribute Syntax Appendix A: Source-Filter Attribute Syntax
This appendix provides an Augmented BNF [ABNF] grammar for expressing This appendix provides an Augmented BNF [ABNF] grammar for expressing
an exclusion or inclusion list of one or more (IPv4 or IPv6) unicast an exclusion or inclusion list of one or more (IPv4 or IPv6) unicast
source addresses. It is intended as an extension to the grammar for source addresses. It is intended as an extension to the grammar for
the Session Description Protocol, as defined in [SDP]. Specifically, the Session Description Protocol, as defined in [SDP]. Specifically,
it describes the syntax for the new "source-filter" attribute field, it describes the syntax for the new "source-filter" attribute field,
which MAY be either a session-level or media-level attribute. which MAY be either a session-level or media-level attribute.
The "connection-address" value in each source filter field MUST match The "connection-address" value in each source filter field MUST match
an existing connection-field value, unless the wildcard connection- an existing connection-field value, unless the wildcard connection-
address value "*" is specified. address value "*" is specified.
source-filter = filter-mode ":" filter-spec source-filter = "source-filter" ":" filter-mode filter-spec
filter-mode = "excl" | "incl" filter-mode = "excl" | "incl"
; either exclusion or inclusion mode ; either exclusion or inclusion mode
filter-spec = nettype address-types dest-address src-list filter-spec = nettype address-types dest-address src-list
; nettype is as defined in [SDP].
address-types = "*" | addrtype address-types = "*" | addrtype
; "*" for all address types (both IP4 and IP6), ; "*" for all address types (both IP4 and IP6),
; but only when <dest-address> and <src-list> ; but only when <dest-address> and <src-list>
; reference FQDNs ; reference FQDNs.
; addrtype is as defined in [SDP].
dest-address = "*" | IP4-address | IP6-address | FQDN dest-address = "*" | IP4-address | IP6-address | FQDN
; "*" applies to all connection-address values ; "*" applies to all connection-address values.
; IP4-address, IP6-address, FQDN are as defined
; in [SDP].
src-list = *(addr SP) addr src-list = *(addr SP) addr
; one or more unicast source addresses (in standard ; one or more unicast source addresses (in standard
; IPv4 or IPv6 ASCII-notation form) or FQDNs ; IPv4 or IPv6 ASCII-notation form) or FQDNs.
; SP is the ASCII 'space' character (0x20) ; SP is the ASCII 'space' character (0x20).
; addr is as defined in [SDP].
References
[CA-96.21] CERT Advisory CA-96.21, "TCP SYN Flooding and IP
Spoofing Attacks," September 1996
[ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax
Specifications: ABNF," RFC 2234, November 1997
[IGMPv1] S. Deering, "Host Extensions for IP Multicasting," RFC
1112 (STD 5), August 1989
[MSF API] D. Thaler, B. Fenner, B. Quinn, "Socket Interface
Extensions for Multicast Source Filters,"
Work in progress
[RTCP-SSM] J. Chesterfield, E. Schooler, J. Ott
RTCP Extensions for Single-Source Multicast Sessions
with Unicast Feedback, Work in progress, February 2002
[SDP] M. Handley, V. Jacobson, "SDP: Session Description
Protocol," RFC 2327, April 1998
[SSM] Bhattacharyya, S. et al., "An Overview of Source-Specific
Multicast (SSM)", Work in progress, March 2002.
[UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
and ISO 10646," RFC 2044, October 1996
Authors' Addresses
Bob Quinn
Celox Networks
2 Park Central Drive
Southborough, MA 01772
phone: 508-305-7000
email: bquinn (at) celoxnetworks.com
Ross Finlayson Expires 15 August 2003 15 February 2003
Live Networks, Inc. (LIVE.COM)
650 Castro St., suite 120-196
Mountain View, CA 94041
email: finlayson (at) live.com
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