Internet DRAFT - draft-kermode-sadp
draft-kermode-sadp
Malloc Working Group Roger Kermode
Internet Engineering Task Force Motorola
INTERNET-DRAFT
8 November 1998
Expires 8 May 1999
Scoped Address Discovery Protocol (SADP)
<draft-kermode-sadp-00.txt>
Status of this Memo
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are valid for a maximum of six months and may be
updated, replaced, or obsoleted by other documents at any time. It
is inappropriate to use Internet Drafts as reference material or to
cite them other than as a "work in progress".
Abstract
This document defines a protocol, the Scoped Address Discovery
Protocol (SADP), for discovering the scoped multicast address(es)
associated with a session at particular scopes within a
hierarchically nested set of multicast zones. SADP is designed to
work within the context of Multicast Address Allocation Architecture
[MAAA] consisting of the MZAP [MZAP], MASC [MASC], and AAP [AAP]
protocols. It is intended that SADP will provide the necessary
general services for reliable multicast and searching applications to
use expanding-zone searches in lieu of the well known, but less
efficient expanding-ring search.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
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Contents
Abstract. . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Introduction. . . . . . . . . . . . . . . . . . . . . 3
2. Overview. . . . . . . . . . . . . . . . . . . . . . . 4
3. Usage . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Session Identifiers . . . . . . . . . . . . . . . . 6
3.2 Session Member Operation. . . . . . . . . . . . . . 6
3.3 SADP Server Operation . . . . . . . . . . . . . . . 7
4. Packet Formats. . . . . . . . . . . . . . . . . . . . 8
4.1 SADP Request. . . . . . . . . . . . . . . . . . . . 10
4.2 SADP Response . . . . . . . . . . . . . . . . . . . 10
5. Constants . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . 12
7. Acknowledgements. . . . . . . . . . . . . . . . . . . 12
8. References. . . . . . . . . . . . . . . . . . . . . . 12
9. Author's Address. . . . . . . . . . . . . . . . . . . 13
10. Full Copyright Statement. . . . . . . . . . . . . . . 13
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1. Introduction
Administrative scoping [RFC2365] provide a useful means for limiting
the spread of IP multicast traffic acros the Internet. Unlike Time-
To-Live (TTL) scoping, administrative scoping provides the means to
ensure that, for a given scope and ignoring packet loss, the same set
of nodes will receive a message, regardless of which node sent the
message. Thus, the use of administrative scoping greatly simplifies
the design of multicast protocols that require localization, since
the non-reception of sent packets is solely due to loss and not
design.
The Multicast Zone Announcement Protocol (MZAP) [MZAP] will provide
applications with the means for discovering the various scopes that
are locally visible at each point in the Internet. In addition, MZAP
will also provide the means for determining and announcing which
scope zones completely encapsulate others. This additional ability
will allow scope zones to be arranged into hierarchies which
applications can then used expanding zone searches instead of less
efficient and more problematic expanding-ring (TTL) searches. One
example of how expanding-zone searches provide increased localization
can be found in the Scoped Hybrid Automatic Repear reQuest with
Forward Error Correction (SHARQFEC) reliable multicast protocol
[SHARQFEC].
While expanding-ring searches use one multicast address and
increasing TTLs, expanding-zone searches involve changing the
multicast addresses for each attempt at a different scope. SADP
builds upon the Multicast Address Allocation Architecture [MAAA] by
adding a new service that allows applications to discover the
relevant multicast address(es) associated with a session at each
level in a hierarchy of scope zones. SADP does not provide the means
to allocate an address should one not be present for a session in a
particular zone. In this case the application should use the Address
Allocation Protocol (AAP) [AAP] to allocate a new address for the
scope, which can then be announced to other application instances
within the scope.
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].
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2. Overview
Administrative scoping affords the ability to create network
partitions or zones in which multicast traffic addressed to one of a
block of addresses assigned to that zone will be limited to that
zone. The boundary of the zone is enforced by Zone Border Routers
(ZBRs) that reside at the edges of the zone. ZBRs must be carefully
configured so that traffic addressed within the zone does not pass
outside the zone. This can be a non trivial task, and hence the
Multicast Zone Announcement Protocol (MZAP) [MZAP], which is used to
announce the existence of zones, also provides the mechanisms to
detect ZBR misconfigurations.
. . . . . . . . . +B+------>
. . /
. *
. <---+A*--------+C+--->
. + .
. / .
. Zone X <--- .
. . . . . . ...
A, B, C - Routers * - border interface + - interface . - border
Figure 1: Admin scope zone border example
Zones may be of different sizes and can also overlap. In addition to
the services of zone announcement and fault detection, MZAP also
provides mechanisms for determining and announcing the existence of
zones that nest inside others as shown in Figure 2.
+-----------+ +-----------+ +-------------+
| zone a | | zone c | | zone e |
| +------+| | +------+ | . . . . .|..
| |zone b|| | |zone d| | : zone f | :
| +------+| | | | | : | :
+-----------+ +----+------+ +-------------+ :
:. . . . ..:
(a) "Contained" (b) "Common Border" (c) "Overlap"
zone b nests zone d nests zones e and f
inside zone a inside zone c do not nest
Figure 2: Zone nesting examples
This feature allows admin scope zones to be arranged in a hierarchy
as shown in Figure 3. The ability to nest admin scope zones in
hierarchies like that shown in Figure 3 is useful since it affords
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localization through expanding-zone searches. For example, consider a
distributed application with session members distributed evenly
through out zone a. A session member in zone e, would perform a
search by multicasting a query within zone e, and if unsuccessful,
expand the scope to search in zone b, and eventually zone a if so
needed.
. . . . . . . . . . . . . . . . ..
. zone a . Zone Boundaries
. . . = zone a
. ______________ ______________ . - = zones b,c
. / zone b \ / zone c \ . # = zones d,e,f, & g
.| | | |.
.| #### #### | | #### #### |.
.| #zone# #zone# | | #zone# #zone# |.
.\ # d # # e # | | # f # # g # /.
.\ ### #### / \ #### #### /.
.\___________/ \____________/.
. . . . . . . . . . . . . . . . ..
Figure 3 : Zone Nesting Hierarchy example
In order for expanding-zone searches to be feasible, session members
must be able to determine two things:
o which zones are involved in the hierarchy for a particular session.
o what address(es) are to be used for communicating with other
session members within the zones involved in the hierarchy.
SADP affords the ability to discover this information by using a
single multicast group at each scope [SADP-RELATIVE-GROUP] for
communication between SADP servers and the members of various
sessions. New members to a session use the channels provided by the
addresses to query existing SADP servers and session members as to
which specific zones are valid and which zones to use. Since there is
only one multicast address used per zone for this purpose, members of
a particular session will ignore traffic intended for members of
another session.
3. Usage
In this section we summarize how session members can use SADP to
determine which admin zones are used by the session's hierarchy and
also the address(es) within these zones that are used by the current
session members should such addresses exist.
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3.1 Session Identifiers
Each session that uses admin scoping will use a Globally Unique
Session Identifier (GUSID) that will distinguish it from all other
sessions. This GUSID will consists of a 128bit integer that is
allocated dynamically using the process described in [UUID]. The
GUSID will be allocated by the session creator and will be used to
associate traffic with a particular session regardless of which
multicast scoped address the traffic is sent to.
3.2 Session Member Operation
Several predefined administrative scopes already exist [RFC2365]:
o Link Local: Traffic is only carried across one physical link.
o Local: Traffic is restricted to a specific network region.
o Global: The entire multicast enabled network.
By definition Link Local zones nest inside Local zone which in turn
nests inside the Global zone. Other zones may exist between the local
and global scopes. These zones are constructed by the union of two or
more local zones and are announced to routers within their confines
using MZAP [MZAP].
The general algorithm that new members to a session should use to
determine which zones and addresses are involved in the hierarchy for
a particular session is as follows:
1) Determine the GUSID, largest zone, and addresses for the largest
zone for the session. (this task is beyond the scope of this
document, but can be assumed to involve some kind of out-of-band
communication.)
2) Starting with the SADP group [SADP-RELATIVE-GROUP] for the
local scope, issue a SADP Request (SADP_REQ) message
containing the GUSID address.
3) Wait for a response on the SADP [SADP-RELATIVE-GROUP] address
for at least [SADP-REQ-TIMEOUT] seconds. If no response is
heard increase the scope to the next largest zone and repeat step
2. In cases where there are two non-nesting zones larger than the
current try one zone and then the other, should the first zone not
result in a reply.
4) Continue steps 2) and 3) until the largest zone has been queried
or a response has been heard.
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In cases where the scope must be increased in order to find a session
member that can reply, the new session member MAY decide to add
levels to the hierarchy in order to increase localization for future
session members. New session members that decide to take this step
will use the existing addresses as discovered using SADP and request
new ones using AAP [AAP].
SADP servers and existing session members, upon hearing an SADP_REQ
message from a new session member will issue an SADP Response
(SADP_RESP) after waiting for a random amount of time (T) that is
calculated as follows:
Choose a random value X from a uniform random interval [0:1]
Let C = 256
Set T = [SADP-SUPPRESSION-INTERVAL] log( C*X + 1) / log(C)
Should a member receive a SADP_RESP before its timer it expires it
SHALL suppress its own response. This method ensures that close to
one session member will respond.
3.2 SADP Server Operation
Were SADP to be deployed in a wide scale session with the members of
various sessions to use SADP between each other it would quickly
cause catastrophic congestion. The reason for this is that whenever a
new node joined a sparsely populated session with a large maximum
scope, it would inevitably end up sending SADP_REQs to every scope up
until the largest scope. Thus the highly likely occurrence of having
a global and continental scope zones combined with numerous sparse
sessions (probably on the order of 10,000 to 100,000) would quickly
cause SADP_REQ flooding at the continental scope.
To address this shortcoming SADP allows, and in fact encourages, the
deployment of SADP servers. These servers subscribe to the [SADP-
RELATIVE-GROUP] for each zone they are in and cache the SADP_RESP
messages they receive at each scope. Having cached and merged the
responses for sessions at various scopes, they can then respond to
SADP_REQs heard at lower scopes using the information heard at the
larger scope(s). Should a SADP server hear a SADP_REQ at some
intermediate scope it MUST NOT announce address information for
scopes smaller than one on which the SADP_REQ was received.
The effect of allowing larger-scoped information to be announced at
lower scopes by SADP servers significantly reduces the number of
scopes a new session will have to query. New session members now need
only expand the scope until a SADP server is found. This is a marked
improvement over the case where no SADP servers exist and the search
must continue until an existing session member is found.
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Scope b Boundary
Scope a : Scope a and Scope b
_________ : ____________ _____________
/ \ : / \ / \
|Source at| _____:___\ |SADP Server | /___________ | New Session |
|Scope a | SADP_RESP/ | Scopes a,b | \ SADP_REQ | Member |
\_________/ : \____________/ ___________\ | Scopes a,b |
: SADP_RESP/ \_____________/
:
Figure 4 : SADP Server acting as proxy session member
4. Packet Formats
All SADP messages are sent over UDP, with a destination port of
[SADP-PORT]. THe common SADP message header (which follows the UDP
header), is shown below,
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | PTYPE |NumScop|AddrFam| NameLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Origin |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (Hi) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (Mid Hi) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (Mid Lo) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (Lo) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Name |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding (if needed) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Authentication Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version: 8 bits
The version defined in this document is version 0.
Packet Type (PTYPE): 8 bits
The packet types defined in this document are:
0: SADP Request
1: SADP Response
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Number of Scope Entries (NumScop) : 4 bits
The number of scope entries present within a SADP_RESP message.
This field should be set to zero for SADP_REQ messages.
Address Family (AddrFam): 4 bits
This indicates the format of the following packet. The following
values are defined by this document:
0: IPv4
1: IPv6
Message Origin: 32 bits (IPv4) or 128 bits (IPv6)
This gives the IP address of the interface that originated the
message.
Session ID Address: 128 bits
This 128 bit number uniquely identifies a session.
Name Len:
The length, in bytes, of the Session Name field.
Session Name: multiple of 8 bits
The Zone Name is an ISO 10646 character string in UTF-8 encoding
[RFC2279] indicating the name given to the session (e.g.:
``42ndIETF-Chicago''). It should be relatively short and MUST be
less than 256 bytes in length. All the session members SHOULD be
configured to give the same Session Name, or a zero length string
MAY be given. A zero length string is taken to mean that another
session member is expected to be configured with the session
name. Having ALL the members of a session announce zero length
names should be considered an error.
Padding (if needed):
The SADP header is padded with null bytes until it is 4-byte
aligned.
Authentication Block:
The Authentication Block provides information which can be used
to confirm that the sender of the SADP message is a valid member
of the session. Session Members that cannot confirm that the
sender of an SADP Request Message MAY ignore it, while new
session members that receiver an SADP Response Message MUST
ignore it. (the format of the authentication block is to be
decided)
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4.1 SADP Request
SADP Request (SADP_REQ) Messages have PTYPE=0, and are sent by new
session members that wish to learn which administrative scopes and
multicast addresses to use within a particular session. SADP_REQ
Messages are sent according to the algorithm described in 3.2.
4.2 SADP Response
The SADP Response (SADP_RESP) Message has PTYPE=1, and is sent in
response to a SADP_REQ Message. It contains the list of address that
are to be used by a session within each scope. Session members that
transmit SADP Response Messages MUST NOT include zone and address
information for scopes known to be smaller that of the address upon
which the triggering SADP Request Message was received.
The format for a SADP Response Message is shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MSADP Header
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| MBZ | SCOP | NumSessAddr | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone Start Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone Stop Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone 1 Session Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . . . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone 1 Session Address K |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| MBZ | SCOP | NumSessAddr | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone Start Address N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone Stop Address N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone N Session Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . . . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zone N Session Address L |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
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SCOP : 4 bits
The SCOP value associated with the zone as defined in RFC 1884
[RFC1884] for IPv6 and RFC 2365 [RFC2365] for IPv4.
NumSessAddr : 8 bits
The number of session address per scope zone that are included.
Addresses will be listed in ascending order. The correspondence
between address and channel function is the responsibility of
the session application.
MBZ :
Must Be Zero, these bits must be set to zero, but may be used
for other functions later revision of the protocol.
Zone X Start Address : 32 bits (IPv4) or 128 bits (IPv6)
The smallest address for the block of multicast addresses
associated with a zone. If a zone X is valid for the range
239.128.0.0 to 239.128.255.255, this field will be set to
239.128.0.0.
Zone X Stop Address : 32 bits (IPv4) or 128 bits (IPv6)
The largest address for the block of multicast addresses
associated with a zone. If a zone X is valid for the range
239.128.0.0 to 239.128.255.255, this field will be set to
239.128.255.255.
Zone X Session Address Y : 32 bits (IPv4) or 128 bits (IPv6)
Up to Y address may be included for a zone address entry, where
Y is equal to the NumSessAddr value for entry X.
5. Constants
[SADP-RELATIVE-GROUP]: The relative group with each scope zone, to
which session members send SADP Requests and Responses. All sessions
that use administratively scoped multicast MUST subscribe to this
address.
[SADP-REQ-TIMEOUT]: The time after which a session member that sends
SADP Request should wait before concluding that no session members
are present at the current scope. Default value is 3 seconds.
[SADP-SUPPRESSION-INTERVAL]: The interval over which a session member
chooses a random delay before responding to SADP Request. Default
value 2 seconds.
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6. Security Considerations
SADP employs distributed mechanisms to allow new session members to
learn of the existence of session-specific admin scoped multicast
address. This fact lay SADP open to attack by malicious hosts that
could potentially mis-inform new session members of incorrect
addresses, thereby affecting a man-in-the-middle attack.
To prevent attacks of this nature by non-session members from
occurring all SADP messages are signed by the sender. However, this
measure does not prevent malicious hosts from joining a session and
then performing the same attack. Hence, SADP's security depends upon
a suitable gating process for new-member admittance combined with (as
yet to be determined) mechanisms that allow spoofed SADP messages to
be identified for removal before processing.
7. Acknowledgments
The Author would like to acknowledge Mark Handley and Dave Thaler for
the helpful discussions and feedback which helped shape and refine
this document.
8. References
[AAP] Handley, M., "The Address Allocation Protocol", Internet
Draft, August 1998.
[MAAA] Handley, M., Thaler, D., and D. Estrin, "The Internet
Multicast Address Allocation Architecture", Internet
Draft, December 1997.
[MZAP] Handley, M., Thaler, D., "Multicast-Scope Zone
Announcement Protocol (MZAP)",
draft-ietf-mboned-mzap-02.txt, Internet-Draft, August,
1998.
[RFC1884] Hinden, R., Deering, S., "IP Version 6 Addressing
Architecture", RFC 1884, December 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP, RFC 2119, March 1997.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP,
RFC 2365, July 1998.
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[SHARQFEC] Kermode, R., "Scoped Hybrid Automatic Repeat reQuest with
Forward Error Correction (SHARQFEC)", ACM SIGCOMM98,
Vancouver Canada, September 1998.
[UUID] Leach, J., Salz, R., "UUIDs and GUIDs",
draft-leach-uuids-guids-01.txt, Internet-Draft, February,
1998.
9. Author's Address
Roger Kermode
Motorola
Chicago Corporate Research Laboratories
1301 East Algonquiin Rd, MS IL02-2712
Schaumburg, IL 60196
Phone: (847) 538 4587
Email: ark008@email.mot.com
10. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights defined
in the Internet languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
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