Network Working Group David Meyer (Editor)
INTERNET DRAFT Bill Fenner (Editor)
Category Standards Track
September, 2001
Multicast Source Discovery Protocol (MSDP)
<draft-ietf-msdp-spec-12.txt>
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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 draft documents 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 "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
2. Abstract
The Multicast Source Discovery Protocol, MSDP, describes a mechanism
to connect multiple PIM-SM domains together. Each PIM-SM domain uses
its own independent RP(s) and does not have to depend on RPs in other
domains.
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3. Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
4. Introduction
The Multicast Source Discovery Protocol, MSDP, describes a mechanism
to connect multiple PIM-SM domains together. Each PIM-SM domain uses
its own independent RP(s) and does not have to depend on RPs in other
domains. Advantages of this approach include:
o No Third-party resource dependencies on RP
PIM-SM domains can rely on their own RPs only.
o Receiver only Domains
Domains with only receivers get data without globally
advertising group membership.
Note that MSDP may be used with protocols other than PIM-SM, but such
usage is not specified in this memo.
The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED,
SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined
in RFC 2119 [RFC2119].
5. Overview
MSDP-speaking routers in a PIM-SM [RFC2362] domain have a MSDP
peering relationship with MSDP peers in another domain. The peering
relationship is made up of a TCP connection in which control
information is exchanged. Each domain has one or more connections to
this virtual topology.
The purpose of this topology is to allow domains to discover
multicast sources from other domains. If the multicast sources are of
interest to a domain which has receivers, the normal source-tree
building mechanism in PIM-SM will be used to deliver multicast data
over an inter-domain distribution tree.
We envision this virtual topology will essentially be congruent to
the existing BGP topology used in the unicast-based Internet today.
That is, the TCP connections between MSDP peers are likely to be
congruent to the connections in the BGP routing system.
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6. Procedure
When an RP in a PIM-SM domain first learns of a new sender, e.g. via
PIM register messages, it constructs a "Source-Active" (SA) message
and sends it to its MSDP peers. The SA message contains the following
fields:
o Source address of the data source.
o Group address the data source sends to.
o IP address of the RP.
Note that an RP that isn't a DR on a shared network SHOULD NOT
originate SA's for directly connected sources on that shared network.
Each MSDP peer receives and forwards the message away from the RP
address in a "peer-RPF flooding" fashion. The notion of peer-RPF
flooding is with respect to forwarding SA messages. The Multicast RPF
Routing Information Base (MRIB) is examined to determine which peer
towards the originating RP of the SA message is selected. Such a peer
is called an "RPF peer". See section 14 for the details of peer-RPF
forwarding.
If the MSDP peer receives the SA from a non-RPF peer towards the
originating RP, it will drop the message. Otherwise, it forwards the
message to all its MSDP peers (except the one from which it received
the SA message).
When an MSDP peer which is also an RP for its own domain receives a
new SA message, it determines if it has any group members interested
in the group which the SA message describes. That is, the RP checks
for a (*,G) entry with a non-empty outgoing interface list; this
implies that the domain is interested in the group. In this case, the
RP triggers a (S,G) join event towards the data source as if a
Join/Prune message was received addressed to the RP itself. This sets
up a branch of the source-tree to this domain. Subsequent data
packets arrive at the RP which are forwarded down the shared-tree
inside the domain. If leaf routers choose to join the source-tree
they have the option to do so according to existing PIM-SM
conventions. Finally, if an RP in a domain receives a PIM Join
message for a new group G, the RP SHOULD trigger a (S,G) join event
for each SA for that group in its cache.
This procedure has been affectionately named flood-and-join because
if any RP is not interested in the group, they can ignore the SA
message. Otherwise, they join a distribution tree.
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7. Caching
A MSDP speaker MUST cache SA messages. Caching allows pacing of MSDP
messages as well as reducing join latency for new receivers of a
group G at an originating RP which has existing MSDP (S,G) state. In
addition, caching greatly aids in diagnosis and debugging of various
problems.
8. Timers
The main timers for MSDP are: SA-Advertisement-Timer, SA-Hold-Down-
Timer, SA Cache Entry timer, KeepAlive timer, ConnectRetry and Peer
Hold Timer. Each is considered below.
8.1. SA-Advertisement-Timer
RPs which originate SA messages do so periodically as long as there
is data being sent by the source. There is one SA-Advertisement-Timer
covering the sources that an RP may advertise. [SA-Advertisement-
Period] MUST be 180 seconds. An RP MUST not send more than one
periodic SA message for a given (S,G) within an SA Advertisement
interval. Originating periodic SA messages is required to keep
announcements alive in caches. Finally, an originating RP SHOULD
trigger the transmission of an SA message as soon as it receives data
from an internal source for the first time.
8.2. SA-Advertisement-Timer Processing
An RP MUST spread the generation of periodic SA messages over its
reporting interval (i.e. SA-Advertisement-Period). An RP starts the
SA-Advertisement-Timer when the MSDP process is configured. When the
timer expires, an RP resets the timer to [SA-Advertisement-Period]
seconds, and begins the advertisement of its active sources. Active
sources are advertised in the following manner: An RP packs its
active sources into an SA message until the largest MSDP packet that
can be sent is built or there are no more sources, and then sends the
message. This process is repeated periodically within the SA-
Advertisement-Period in such a way that all of the RP's sources are
advertised. Note that since MSDP is a periodic protocol, an
implemenation SHOULD send all cached SA messages when a connection is
established. Finally, the timer is deleted when the MSDP process is
deconfigured.
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8.3. SA Cache Timeout (SA-State Timer)
Each entry in an SA Cache has an associated SA-State Timer. A
(S,G)-SA-State-Timer is started when an (S,G)-SA message is initially
received by a MSDP peer. The timer is reset to [SA-State-Period] if
another (S,G)-SA message is received before the (S,G)-SA-State Timer
expires. [SA-State-Period] MUST NOT be less than [SA-Advertisement-
Period] + [SA-Hold-Down-Period].
8.4. SA-Hold-Down Timer
When an SA message is received which creates (S,G) state, the
(S,G)-SA message will be forwarded if the peer-RPF check succeeds. If
the peer-RPF check succeeds and the (S,G)-SA message is not already
in the SA cache, then the (S,G)-SA-Hold-Down timer is set to [SA-
Hold-Down-Period] seconds. When an (S,G)-SA message is received and
an (S,G) entry already exists, the message is forwarded only if the
(S,G)-SA-Hold-Down timer is not running. [SA-Hold-Down-Period] SHOULD
be set to 30 seconds.
8.5. Peer Hold Timer
If a system has not received any MSDP message within the period
specified by the Hold Timer, then a Notification message with Hold
Timer Expired Error Code MUST be sent and the MSDP connection MUST be
closed. [HoldTime-Period] MUST be at least three seconds. The
recommended value for [HoldTime-Period] is 90 seconds.
The Hold Timer is initialized to [HoldTime-Period] when the peer's
transport connection is established, and is reset to [HoldTime-
Period] when any MSDP message is received. Finally, the timer is
deleted when the peer's transport connection is closed.
8.6. KeepAlive Timer
Once an MSDP transport connection is established, each side of the
connection sends a KeepAlive message and sets a KeepAlive timer. If
the KeepAlive timer expires, the local system sends a KeepAlive
message and restarts its KeepAlive timer.
The KeepAlive timer is set to [KeepAlive-Period] when the peer comes
up. The timer is reset to [KeepAlive-Period] each time an MSDP
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message is sent to the peer, and reset when the timer expires.
Finally, the KeepAlive timer is deleted when the peer's transport
connection is closed.
[KeepAlive-Period] MUST be less than [HoldTime-Period], and MUST be
at least one second. The recommended value for [KeepAlive-Period] is
75 seconds.
8.7. ConnectRetry Timer
The ConnectRetry timer is used by an MSDP peer to transition from
INACTIVE to CONNECTING states. There is one timer per peer, and the
[ConnectRetry-Period] SHOULD be set to 30 seconds. The timer is
initialized to [ConnectRetry-Period] when an MSDP speaker attempts to
actively open a TCP connection to its peer (see section 15, event E2,
action A2 ). When the timer expires, the peer retries the connection
and the timer is reset to [ConnectRetry-Period]. It is deleted if
either the connection transitions into ESTABLISHED state or the peer
is deconfigured.
9. Intermediate MSDP Peers
Intermediate MSDP speakers do not originate periodic SA messages on
behalf of sources in other domains. In general, an RP MUST only
originate an SA for a source which would register to it, and ONLY RPs
may originate SA messages.
10. SA Filtering and Policy
As the number of (S,G) pairs increases in the Internet, an RP may
want to filter which sources it describes in SA messages. Also,
filtering may be used as a matter of policy which at the same time
can reduce state. Only the RP co-located in the same domain as the
source can restrict SA messages. Note, however, that MSDP peers in
transit domains should not filter SA messages or the flood-and-join
model can not guarantee that sources will be known throughout the
Internet (i.e., SA filtering by transit domains can cause undesired
lack of connectivity). In general, policy should be expressed using
MBGP [RFC2283]. This will cause MSDP messages to flow in the desired
direction and peer-RPF fail otherwise. An exception occurs at an
administrative scope [RFC2365] boundary. In particular, a SA message
for a (S,G) MUST NOT be sent to peers which are on the other side of
an administrative scope boundary for G.
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11. SA Requests
A MSDP speaker MAY accept SA-Requests from other MSDP peers. When an
MSDP speaker receives an SA-Request for a group range, it will
respond to the peer with a set of SA entries, in an SA-Response
message, for all active sources in its SA cache sending to the group
requested in the SA-Request message. The peer that sends the request
will not flood the responding SA-Response message to other peers. See
section 17 for discussion of error handling relating to SA requests
and responses.
12. Encapsulated Data Packets
The RP may encapsulate multicast data from the source. An interested
RP may decapsulate the packet, which SHOULD be forwarded as if a PIM
register encapsulated packet was received. That is, if packets are
already arriving over the interface toward the source, then the
packet is dropped. Otherwise, if the outgoing interface list is non-
null, the packet is forwarded appropriately. Note that when doing
data encapsulation, an implementation MUST bound the time during
which packets are encapsulated.
This allows for small bursts to be received before the multicast tree
is built back toward the source's domain. For example, an
implementation SHOULD encapsulate at least the first packet to
provide service to bursty sources.
13. Other Scenarios
MSDP is not limited to deployment across different routing domains.
It can be used within a routing domain when it is desired to deploy
multiple RPs for the same group ranges. As long as all RPs have a
interconnected MSDP topology, each can learn about active sources as
well as RPs in other domains.
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14. MSDP Peer-RPF Forwarding
The MSDP Peer-RPF Forwarding rules are used for forwarding SA
messages throughout an MSDP enabled internet. Unlike the RPF check
used when forwarding data packets, the Peer-RPF check is against the
RP address carried in the SA message.
14.1. Definitions
The following definitions are used in the description of the Peer-RPF
Forwarding Rules:
14.1.1. Multicast RPF Routing Information Base (MRIB)
The MRIB is the multicast topology table. It is typically derived
from the unicast routing table or from other routing protocols such
as multi-protocol BGP [RFC2283].
14.1.2. RPF Route
The RPF route is the route that the MRIB chooses for a given address.
The RPF route for a SA's originating RP is used to select the peer
from which the SA is accepted.
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14.2. Peer-RPF Forwarding Rules
An SA message originated by R and received by X from N is
accepted if N is the peer-RPF neighbor for X, and is discarded
otherwise.
MPP(R,N) MP(N,X)
R ---------....-------> N ------------------> X
SA(S,G,R) SA(S,G,R)
Where MPP(R,N) is an MSDP peering path (zero or more MSDP
peers) between R and N. SA(S,G,R) is an SA message for source
S on group G originated by an RP R. MP(N,X) is an MSDP
peering between N and X.
The peer-RPF neighbor is chosen deterministically, using the
first of the following rules that matches. In particular,
N is the RPF neighbor of X with respect to R if
(i). N == R (X has an MSDP peering with R).
(ii). N is the BGP NEXT_HOP of the active RPF route
for R.
(iii). The active RPF route for R is learned through a
distance-vector or path-vector routing protocol
(e.g. BGP, RIP, DVMRP) and N is the neighbor that
advertised the active RPF route for R if the
route was learned via a distance-vector or
path-vector protocol, or N is the IGP next hop
for if R was learned via a link-state protocol.
(iv). N resides in an AS that is in the AS_PATH of the active
RPF route for R, and N has the highest IP address among
the MSDP peers that reside in ASs in that AS_PATH.
(v). N is configured as the static RPF-peer for R.
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14.3. MSDP static RPF-peer semantics
If none of the rules (i) - (iv) are able to determine an RPF peer for
R, a longest-match lookup is performed in the static RPF peer table.
This table MUST be able to contain a default entry, and SHOULD be
able to contain prefix or per-host (RP) entries. This table
statically maps RP addresses to peers, and allows configuration of
topology that is e.g. unknown to the MRIB.
The result of the longest-match lookup of an RP address R in the
static RPF peer table is an MSDP peer, which is the RPF neighbor for
R.
14.4. MSDP mesh-group semantics
A MSDP mesh-group is a operational mechanism for reducing SA
flooding, typically in an intra-domain setting. In particular, when
some subset of a domain's MSDP speakers are fully meshed, then can be
configured into a mesh-group.
Note that mesh-groups assume that a member doesn't have to forward an
SA to other members of the mesh-group because the originator will
forward to all members. To be able for the originator to forward to
all members (and to have each member also be a potential originator),
the mesh-group must be a full mesh of MSDP peering among all members.
The semantics of the mesh-group are as follows:
(i). If a member R of a mesh-group M receives a SA message from an
MSDP peer that is also a member of mesh-group M, R accepts the
SA message and forwards it to all of its peers that are not
part of any mesh-group. R MUST NOT forward the SA message to
other members of mesh-group M.
(ii). If a member R of a mesh-group M receives a SA message from an
MSDP peer that is not a member of mesh-group M, and the SA
message passes the peer-RPF check, then R forwards the SA
message to all members of mesh-group M.
(iii). Cross mesh-group forwarding
If a member R of a mesh-groups M and N receives an SA
message from an MSDP peer in mesh-group M, R forwards the SA
to its MSDP peers in mesh-group N if it receives that SA
message from a peer that is in the same mesh-group as its
peer-RPF neighbor for that SA.
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For example, consider the case in which three routers (R1, R2,
and R3) and three mesh-groups (A, B, and C) are arranged in a
triangle, e.g.,
[R2] {A,B}
/ \
/ \
/ \
/ \
{A,C} [R1]--------[R3] {B,C}
Now, when R1 receives an SA message from R2 and R1's
peer-RPF neighbor for this SA lies in mesh-group A, R1
forwards the SA message its peers in other mesh-groups
(in particular, R3 in mesh-group C). Similarly, if R3's
peer-RPF neighbor lies in mesh-group B, R3 will forward an
SA message from R2. In this case, both R1 and R3 will send
SA messages to each other (because they share common mesh-group
C), but neither of them will forward any further the SA messages
received from each other (as their peer-RPF neighbors do
not lie in mesh-group C).
Note that since mesh-groups suspend peer-RPF checking of SAs received
from a mesh-group member ((i). above), they allow for mis-
configuration to cause SA looping.
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15. MSDP Connection State Machine
MSDP uses TCP as its transport protocol. In a peering relationship,
one MSDP peer listens for new TCP connections on the well-known port
639. The other side makes an active connect to this port. The peer
with the higher IP address will listen. This connection establishment
algorithm avoids call collision. Therefore, there is no need for a
call collision procedure. It should be noted, however, that the
disadvantage of this approach is that it may result in longer startup
times at the passive side.
An MSDP peer starts in the DISABLED state. MSDP peers establish
peering sessions according to the following state machine:
--------------->+----------+
/ | DISABLED |<----------
| ------>+----------+ \
| / |E1->A1 |
| | | |
| | V |E7->A7
| | +----------+ E3->A3 +--------+
| | | INACTIVE |------->| LISTEN |
| | +----------+ +--------+
| | E2->A2| ^ |E5->A5
| | | | |
| |E7->A6 V |E6 |
| \ +------------+ |
E7->A8 | ------| CONNECTING | |
E8->A9 | +------------+ |
E9->A10| |E4->A4 |
E10->A11| | |
E11->A12| V |
\ +-------------+ /
--------------| ESTABLISHED |<---------
+-------------+
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15.1. Events
E1) Enable MSDP peering with P
E2) Own IP address < P's IP address
E3) Own IP address > P's IP address
E4) TCP established (active side)
E5) TCP established (passive side)
E6) ConnectRetry timer expired
E7) Disable MSDP peering with P
An example of when to do this is when one's own address is
changed)
E8) Hold Timer expired
E9) Authorization failure
E10) Notification TLV received
E11) Error detected
15.2. Actions
A1) Allocate resources for peering with P
Compare one's own and peer's IP addresses
A2) TCP active OPEN
Set ConnectRetry timer to [ConnectRetry-Period]
A3) TCP passive OPEN (listen)
A4) Delete ConnectRetry timer
Send KeepAlive TLV
Set KeepAlive timer to [KeepAlive-Period]
Set Hold Timer to [HoldTime-Period]
A5) Send KeepAlive TLV
Set KeepAlive timer to [KeepAlive-Period]
Set Hold Timer to [HoldTime-Period]
A6) Abort TCP active OPEN attempt
Release resources allocated for peering with P
A7) Abort TCP passive OPEN attempt
Release resources allocated for peering with P
In action sets 8)-12), the action "Close peering session" includes
the following steps:
Close TCP connection
Delete KeepAlive timer
Delete Hold Timer
Release resources allocated for peering with P
A8) Send Notification TLV with Error Code "Cease"
Close peering session
A9) Send Notification TLV with Error Code "Hold Timer Expired"
Close peering session
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A10) Notify management system unless this has already been done by
the security mechanism
Close peering session
A11) Notify management system
If the received Notification TLV's O-bit was cleared, close
peering session. Otherwise, remain in ESTABLISHED state.
A12) Send Notification TLV with appropriate Error Code
Notify management system
If the sent Notification TLV's O-bit was cleared, close peering
session. Otherwise, remain in ESTABLISHED state.
15.3. Peer-specific Events
The following peer-specific events can occur in the ESTABLISHED
state, they do not cause a state transition. Appropriate actions are
listed for each event.
*) KeepAlive timer expired:
-> Send KeepAlive TLV
-> Set KeepAlive timer to [KeepAlive-Period]
*) KeepAlive TLV received:
-> Set Hold Timer to [HoldTime-Period]
*) Source-Active TLV received:
-> Set Hold Timer to [HoldTime-Period]
-> Run Peer-RPF Forwarding algorithm (consider SA-Hold-Down
Timer and SA-State Timer)
-> Set KeepAlive timer to [KeepAlive-Period] for those peers
the Source-Active TLV is forwarded to
-> Send information to PIM-SM
-> Store information in cache
*) Source-Active Request TLV received:
-> Set Hold Timer to [HoldTime-Period]
-> If SA-Requests are accepted, send Source-Active Response
TLV and set KeepAlive timer to [KeepAlive-Period]
*) Source-Active Response TLV received:
-> Set Hold Timer to [HoldTime-Period]
-> If a corresponding SA-Request were previously sent, send
information to PIM-SM. If not, an error has occured
(event 11 above)
-> Store information in cache
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15.4. Peer-independent Events
There are also a number of events that affect more than one peering
session, but still require actions to be performed on a per-peer
basis.
*) SA-Advertisement-Timer expired:
-> Start periodic transmission of Source-Active TLV(s)
-> Set KeepAlive timer to [KeepAlive-Period] each time a
Source-Active TLV is sent
*) MSDP learns of a new active internal source (e.g. PIM-SM
register received for a new source):
-> Send Source-Active TLV
-> Set KeepAlive timer to [KeepAlive-Period]
*) Source-Active Request triggered (event not specified here):
-> Send Source-Active Request TLV
-> Set KeepAlive timer to [KeepAlive-Period]
*) SA-State-Timer expired (one timer per cache entry):
-> Implementation specific, typically mark the cache entry for
deletion
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16. Packet Formats
MSDP messages will be encoded in TLV format. If an implementation
receives a TLV that has length that is longer than expected, the TLV
SHOULD be accepted. Any additional data SHOULD be ignored.
16.1. MSDP TLV format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (8 bits)
Describes the format of the Value field.
Length (16 bits)
Length of Type, Length, and Value fields in octets.
minimum length required is 4 octets, except for
Keepalive messages. The maximum TLV length is 1400.
Value (variable length)
Format is based on the Type value. See below. The length of
the value field is Length field minus 3. All reserved fields
in the Value field MUST be transmitted as zeros and ignored on
receipt.
16.2. Defined TLVs
The following TLV Types are defined:
Code Type
===========================================================
1 IPv4 Source-Active
2 IPv4 Source-Active Request
3 IPv4 Source-Active Response
4 KeepAlive
5 Notification
Each TLV is described below.
In addition, the following TLV Types are assigned but not described
in this memo:
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Code Type
===========================================================
6 MSDP traceroute in progress
7 MSDP traceroute reply
16.2.1. IPv4 Source-Active TLV
The maximum size SA message that can be sent is 9192 octets. The 9192
octet size does not include the TCP, IP, layer-2 headers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | x + y | Entry Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Sprefix Len | \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \
| Group Address | ) z
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
| Source Address | /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
IPv4 Source-Active TLV is type 1.
Length x
Is the length of the control information in the message. x is
8 octets (for the first two 32-bit quantities) plus 12 times
Entry Count octets.
Length y
If 0, then there is no data encapsulated. Otherwise an IPv4
packet follows and y is the length of the total length field
of the IPv4 header encapsulated. If there are multiple SA TLVs
in a message, and data is also included, y must be 0 in all SA
TLVs except the last one and the last SA TLV must reflect the
source and destination addresses in the IP header of the
encapsulated data.
Entry Count
Is the count of z entries (note above) which follow the RP
address field. This is so multiple (S,G)s from the same domain
can be encoded efficiently for the same RP address.
RP Address
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The address of the RP in the domain the source has become
active in.
Reserved
The Reserved field MUST be transmitted as zeros and MUST be
ignored by a receiver.
Sprefix Len
The route prefix length associated with source address.
This field MUST be transmitted as 32 (/32). An Invalid
Sprefix Len Notification SHOULD be sent upon receipt
of any other value.
Group Address
The group address the active source has sent data to.
Source Address
The IP address of the active source.
Multiple SA TLVs MAY appear in the same message and can be batched
for efficiency at the expense of data latency. This would typically
occur on intermediate forwarding of SA messages.
16.2.2. IPv4 Source-Active Request TLV
The Source-Active Request is used to request SA-state from a MSDP
peer. If an RP in a domain receives a PIM Join message for a group,
creates (*,G) state and wants to know all active sources for group G,
it may send an SA-Request message for the group.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 8 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
IPv4 Source-Active Request TLV is type 2.
Reserved
Must be transmitted as zero and ignored on receipt.
Group Address
The group address the MSDP peer is requesting.
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
16.2.3. IPv4 Source-Active Response TLV
The Source-Active Response is sent in response to a Source-Active
Request message. The Source-Active Response message has the same
format as a Source-Active message but does not allow encapsulation of
multicast data.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | x | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
IPv4 Source-Active Response TLV is type 3.
Length x
Is the length of the control information in the message. x is 8
octets (for the first two 32-bit quantities) plus 12 times Entry
Count octets.
16.2.4. KeepAlive TLV
A KeepAlive TLV is sent to an MSDP peer if and only if there were no
MSDP messages sent to the peer within [KeepAlive-Period] seconds.
This message is necessary to keep the MSDP connection alive.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length of the message is 3 octets which encompasses the one octet
Type field and the two octet Length field.
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
16.2.5. Notification TLV
A Notification message is sent when an error condition is detected,
and has the following form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | x + 5 |O| Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error subcode | ... |
+-+-+-+-+-+-+-+-+ |
| Data |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The Notification TLV is type 5.
Length
Length is a two octet field with value x + 5, where x is
the length of the notification data field.
O-bit
Open-bit. If clear, the connection will be closed.
Error code
This 7-bit unsigned integer indicates the type of Notification.
The following Error Codes have been defined:
Error Code Symbolic Name Reference
1 Message Header Error Section 17.1
2 SA-Request Error Section 17.2
3 SA-Message/SA-Response Error Section 17.3
4 Hold Timer Expired Section 17.4
5 Finite State Machine Error Section 17.5
6 Notification Section 17.6
7 Cease Section 17.7
Error subcode:
This one-octet unsigned integer provides more specific information
about the reported error. Each Error Code may have one or more Error
Subcodes associated with it. If no appropriate Error Subcode is
defined, then a zero (Unspecific) value is used for the Error Subcode
field, and the O-bit must be cleared (i.e. the connection will be
closed). The used notation in the error description below is: MC =
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
Must Close connection = O-bit clear; CC = Can Close connection =
O-bit MAY be cleared.
Message Header Error subcodes:
0 - Unspecific (MC)
2 - Bad Message Length (MC)
3 - Bad Message Type (CC)
SA-Request Error subcodes (the O-bit is always clear):
0 - Unspecific (MC)
1 - Invalid Group (MC)
SA-Message/SA-Response Error subcodes
0 - Unspecific (MC)
1 - Invalid Entry Count (CC)
2 - Invalid RP Address (MC)
3 - Invalid Group Address (MC)
4 - Invalid Source Address (MC)
5 - Invalid Sprefix Length (MC)
6 - Looping SA (Self is RP) (MC)
7 - Unknown Encapsulation (MC)
8 - Administrative Scope Boundary Violated (MC)
Hold Timer Expired subcodes (the O-bit is always clear):
0 - Unspecific (MC)
Finite State Machine Error subcodes (the O-bit is always clear):
0 - Unspecific (MC)
1 - Unexpected Message Type FSM Error (MC)
Notification subcodes (the O-bit is always clear):
0 - Unspecific (MC)
Cease subcodes (the O-bit is always clear):
0 - Unspecific (MC)
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
17. MSDP Error Handling
This section describes actions to be taken when errors are detected
while processing MSDP messages. MSDP Error Handling is similar to
that of BGP [RFC1771].
When any of the conditions described here are detected, a
Notification message with the indicated Error Code, Error Subcode,
and Data fields is sent. In addition, the MSDP connection MAY be
closed. If no Error Subcode is specified, then a zero (Unspecific)
must be used.
The phrase "the MSDP connection is closed" means that the transport
protocol connection has been closed and that all resources for that
MSDP connection have been deallocated.
17.1. Message Header Error Handling
All errors detected while processing the Message Header are indicated
by sending the Notification message with Error Code Message Header
Error. The Error Subcode describes the specific nature of the error.
The Data field contains the erroneous Message (including the message
header).
If the Length field of the message header is less than 4 or greater
than 1400, or the length of a KeepAlive message is not equal to 3,
then the Error Subcode is set to Bad Message Length.
If the Type field of the message header is not recognized, then the
Error Subcode is set to Bad Message Type.
17.2. SA-Request Error Handling
The SA-Request Error code is used to signal the receipt of a SA
request at a MSDP peer when an invalid group address requested.
When a MSDP peer receives a request for an invalid group, it returns
the following notification:
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 12 |O| 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17.3. SA-Message/SA-Response Error Handling
The SA-Message/SA-Response Error code is used to signal the receipt
of a erroneous SA Message at an MSDP peer, or the receipt of an SA-
Response Message by a peer that did not issue a SA-Request. It has
the following form:
17.3.1. Invalid Entry Count (IEC)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 6 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Entry Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17.3.2. Invalid RP Address
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 12 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
17.3.3. Invalid Group Address
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 12 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17.3.4. Invalid Source Address
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 12 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17.3.5. Invalid Sprefix Length (ISL)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 6 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | Sprefix Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17.3.6. Looping SAs (Self is RP in received SA)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | x + 5 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | SA Message ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length x
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
x is the length of the looping SA message contained in the data
field of the Notification message.
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
17.3.7. Unknown Encapsulation
This notification is sent on receipt of SA data that is encapsulated
in an unknown encapsulation type. See section 18 for known
encapsulations.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | x + 5 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 | SA Message ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length x
x is the length of the SA message (which contained data which
was encapsulated in some unknown way) that is contained in the
data field of the Notification message.
17.3.8. Administrative Scope Boundary Violated
This notification is used when an SA message is received for a group
G from a peer which is across an administrative scope boundary for G.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 12 |O| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
17.4. Hold Time Expired
If a system has not received any MSDP message within the period
specified in the Hold Timer, the notification message with Hold Timer
Expired Error Code and no additional data MUST be sent and the MSDP
connection closed.
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
17.5. Finite State Machine Error Handling
Any error detected by the MSDP Finite State Machine (e.g., receipt of
an unexpected event) is indicated by sending the Notification message
with Error Code Finite State Machine Error.
17.6. Notification Message Error Handling
If a node sends a Notification message, and there is an error in that
message, and the O-bit of that message is not clear, a Notification
with O-bit clear, Error Code of Notification Error, and subcode
Unspecific must be sent. In addition, the Data field must include
the Notification message that triggered the error. However, if the
erroneous Notification message had the O-bit clear, then any error,
such as an unrecognized Error Code or Error Subcode, should be
noticed, logged locally, and brought to the attention of the
administrator of the remote node.
17.7. Cease
In absence of any fatal errors (that are indicated in this section),
an MSDP node may choose at any given time to close its MSDP
connection by sending the Notification message with Error Code Cease.
However, the Cease Notification message MUST NOT be used when a fatal
error indicated by this section does exist.
18. SA Data Encapsulation
This section describes UDP, GRE, and TCP encapsulation of data
packets to be included with SA messages. Encapsulation type is a
configuration option.
18.1. UDP Data Encapsulation
Data packets MAY be encapsulated in UDP. In this case, the UDP
pseudo-header has the following form:
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Origin RP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Source port, Destination Port, Length, and Checksum are used
according to RFC 768. Source and Destination ports are known via
an implementation-specific method (e.g. per-peer configuration).
Checksum
The checksum is computed according to RFC 768 [RFC768].
Originating RP Address
The Originating RP Address is the address of the RP sending
the encapsulated data.
18.2. GRE Encapsulation
MSDP SA-data MAY be encapsulated in GRE using protocol type [MSDP-
GRE-ProtocolType]. The GRE header and payload packet have the
following form:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Reserved0 | Ver | [MSDP-GRE-ProtocolType] |\
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GRE Header
| Checksum (optional) | Reserved1 |/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating RP IPv4 Address |\
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Payload
| (S,G) Data Packet .... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
18.2.1. Encapsulation and Path MTU Discovery [RFC1191]
Existing implementations of GRE, when using IPv4 as the Delivery
Header, do not implement Path MTU discovery and do not set the Don't
Fragment bit in the Delivery Header. This can cause large packets to
become fragmented within the tunnel and reassembled at the tunnel
exit (independent of whether the payload packet is using PMTU). If a
tunnel entry point were to use Path MTU discovery, however, that
tunnel entry point would also need to relay ICMP unreachable error
messages (in particular the "fragmentation needed and DF set" code)
back to the originator of the packet, which is not required by the
GRE specification [RFC2784]. Failure to properly relay Path MTU
information to an originator can result in the following behavior:
the originator sets the don't fragment bit, the packet gets dropped
within the tunnel, but since the originator doesn't receive proper
feedback, it retransmits with the same PMTU, causing subsequently
transmitted packets to be dropped.
18.3. TCP Data Encapsulation
As discussed earlier, encapsulation of data in SA messages MAY be
supported for backwards compatibility with legacy MSDP peers.
19. IANA Considerations
The IANA should assign 0x0009 from the IANA SNAP Protocol IDs [IANA]
to MSDP-GRE-ProtocolType.
20. Security Considerations
An MSDP implementation MUST use IPsec [RFC2401] to secure control
messages. In particular, the TCP connection between MSDP peers MUST
be secured using IPsec. When encapsulating data packets in GRE,
security should be relatively similar to security in a normal IPv4
network, as routing using GRE follows the same routing that IPv4 uses
natively. Route filtering will remain unchanged. However packet
filtering at a firewall requires either that a firewall look inside
the GRE packet or that the filtering is done on the GRE tunnel
endpoints. In those environments in which this is considered to be a
security issue it may be desirable to terminate the tunnel at the
firewall.
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
21. Acknowledgments
The editors would like to thank the original authors, Dino Farinacci,
Yakov Rehkter, Peter Lothberg, Hank Kilmer, and Jermey Hall for their
orginal contribution to the MSDP specification. In addition, Bill
Nickless, John Meylor, Liming Wei, Manoj Leelanivas, Mark Turner,
John Zwiebel, Cristina Radulescu-Banu, Brian Edwards, Selina
Priestley and IJsbrand Wijnands provided useful and productive design
feedback and comments. In addition to many other contributions, Tom
Pusateri, Kristofer Warell, Henning Eriksson, and Thomas Eriksson
helped to clarify the connection state machine, Dave Thaler helped to
clarify the Notification message types. Ravi Shekhar helped clarify
the semantics of mesh-groups, and countless others helped to clarify
the Peer-RPF rules.
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
22. Editors' Address:
David Meyer
Sprint
12502 Sunrise Valley Drive
Reston VA, 20191
Email: dmm@sprint.net
Bill Fenner
AT&T Labs -- Research
75 Willow Road
Menlo Park, CA 94025
Email: fenner@research.att.com
[Page 31]
Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
23. REFERENCES
[IANA] http://www.iana.org
[RFC768] Postel, J. "User Datagram Protocol", RFC 768, August,
1980.
[RFC1191] Mogul, J., and S. Deering, "Path MTU Discovery",
RFC 1191, November 1990.
[RFC1771] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
(BGP-4)", RFC 1771, March 1995.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March, 1997.
[RFC2283] Bates, T., Chandra, R., Katz, D., and Y. Rekhter.,
"Multiprotocol Extensions for BGP-4", RFC 2283,
February 1998.
[RFC2362] Estrin D., et al., "Protocol Independent Multicast -
Sparse Mode (PIM-SM): Protocol Specification", RFC
2362, June 1998.
[RFC2365] Meyer, D. "Administratively Scoped IP Multicast", RFC
2365, July, 1998.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC 2401, November 1998.
[RFC2784] Farinacci, D., et al., "Generic Routing Encapsulation
(GRE)", RFC 2784, March 2000.
24. Full Copyright Statement
Copyright (C) The Internet Society (2001). 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
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Internet Draft draft-ietf-msdp-spec-12.txt September, 2001
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into 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.
[Page 33]
