E7->A8 | |E4->A4 |
E8->A8 | | |
E9->A8 | V |
\ +-------------+ /
--------------| ESTABLISHED |<---------
+-------------+
| ^
| |
E10->A9 \______/
11.1. 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 (e.g., when one’s own address is
changed)
E8) Hold Timer expired
E9) MSDP TLV format error detected
E10) Any other error detected
11.2. 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
A8) Close the TCP connection
Release resources allocated for peering with P
A9) Drop the packet
11.3. 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
-> 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
11.4. 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]
*) SG-State-Timer expired (one timer per cache entry):
-> Implementation specific, typically mark the cache entry
for deletion
12. Packet Formats
MSDP messages are encoded in TLV format. If an implementation
receives a TLV whose length exceeds the maximum TLV length specified
below, the TLV SHOULD be accepted. Any additional data, including
possible next TLV’s in the same message, SHOULD be ignored, and the
MSDP session should not be reset.
12.1. 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 9192.
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.
12.2. 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 Reserved (Previously: Notification)
Each TLV is described below.
In addition, the following TLV Types are assigned but not described
in this memo:
Code Type
====================================================
6 MSDP traceroute in progress
7 MSDP traceroute reply
12.2.1. 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 value of the total length field in the header
of the encapsulated IP packet. If there are multiple (S,G) entries
in an SA message, only the last entry may have encapsulated data and
it must reflect the source and destination addresses in the header
of the encapsulated IP packet.
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. An SA message
containing encapsulated data typically has an entry count of 1
(i.e., only contains a single entry, for the (S,G) representing the
encapsulated packet).
RP Address
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).
Group Address
The group address the active source has sent data to.
Source Address
The IP address of the active source.
Multiple (S,G) entries MAY appear in the same SA and can be batched
for efficiency at the expense of data latency. This would typically
occur on intermediate forwarding of SA messages.
12.2.2. 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.
13. MSDP Error Handling
If an MSDP message is received with a TLV format error, the session
SHOULD be reset with that peer. MSDP messages with other errors,
such as unrecognized type code, received from MSDP peers, SHOULD be
silently discarded and the session SHOULD not be reset.
14. SA Data Encapsulation
As discussed earlier, TCP encapsulation of data in SA messages MAY be
supported for backwards compatibility with legacy MSDP peers.
15. Applicability Statement
MSDP is used primarily in two deployment scenarios:
15.1. Between PIM Domains
MSDP can be used between PIM domains to convey information about
active sources available in other domains. MSDP peering used in such
cases is generally one to one peering, and utilizes the deterministic
peer-RPF rules described in this spec (i.e., does not use mesh-
groups). Peerings can be aggregated on a single MSDP peer, typically
from one to hundreds of peerings, similar in scale, although not
necessarily consistent, with BGP peerings.
15.2. Between Anycast-RPs
MSDP is also used between Anycast-RPs [RFC3446] within a PIM domain
to synchronize information about the active sources being served by
each Anycast-RP peer (by virtue of IGP reachability). MSDP peering
used in this scenario is typically based on MSDP mesh groups, where
anywhere from two to tens of peers can comprise a given mesh group,
although more than ten is not typical. One or more of these mesh-
group peers may then also have additional one-to-one peering with
msdp peers outside that PIM domain as described in scenario A, for
discovery of external sources. MSDP for anycast-RP without external
MSDP peering is a valid deployment option and common.
16. Intellectual Property
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF’s procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
17. Acknowledgments
The editors would like to thank the original authors, Dino Farinacci,
Yakov Rehkter, Peter Lothberg, Hank Kilmer, and Jermey Hall for their
original 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, IJsbrand Wijnands, Tom Pusateri, Kristofer Warell, Henning
Eriksson, Thomas Eriksson, Dave Thaler, and Ravi Shekhar provided
useful and productive design feedback and comments. Toerless Eckert,
Leonard Giuliano, Mike McBride, David Meyer, John Meylor, Pekka
Savola, Ishan Wu, and Swapna Yelamanchi contributed to the final
version of the document.
18. Security Considerations
An MSDP implementation MUST implement Keyed MD5 [RFC2385] to secure
control messages, and MUST be capable of interoperating with peers
that do not support it. However, if one side of the connection is
configured with Keyed MD5 and the other side is not, the connection
SHOULD NOT be established.
In addition, to mitigate state explosion during denial of service and
other attacks, SA filters and limits SHOULD be used with MSDP to
limit the sources and groups that will be passed between RPs
[DEPLOY]. These filtering and limiting functions may include, for
example, access lists of source or group addresses which should not
be propagated to other domains using MSDP, the absolute highest
acceptable number of SA-state entries or a rate-limit of for the
creation of new SA-state entries after the connection has been
established.
If follow-on work is done in this area, a more robust integrity
mechanism, such as HMAC-SHA1 [RFC2104, RFC2202] ought to be employed.
19. IANA Considerations
This document creates a new namespace called "MSDP TLV Values" that
the IANA will manage. The initial seven MSDP TLV values are
specified in Section 12.2. The following two sections describe the
rules for allocating new MSDP TLV values.
19.1. IANA Allocated TLV Range
MSDP TLV values in the range [8,200] (inclusive) are to be allocated
using an IESG Approval or Standards Action process [RFC2434].
19.2. Experimental TLV Range
TLV values in the range [201,255] (inclusive) are allocated for
experimental use.
20. References
20.1. Normative References
[RFC1142] Oran, D., Ed., "OSI IS-IS Intra-domain Routing
Protocol", RFC 1142, February 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
1998.
[RFC2858] Bates, T., Rekhter, Y., Chandra, R. and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858, June
2000.
[RFC2362] Estrin, D., Farinacci, D., Helmy, A., Thaler, D.,
Deering, S., Handley, M., Jacobson, V., Lin, C.,
Sharma, P. and L. Wei, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol
Specification", RFC 2362, June 1998.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast",
BCP 23, RFC 2365, July 1998.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the
TCP MD5 Signature Option", RFC 2385, August 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
[RFC3446] Kim, D., Meyer, D., Kilmer, H. and D. Farinacci,
"Anycast Rendezvous Point (RP) Mechanism using
Protocol Independent Multicast (PIM) and Multicast
Source Discovery Protocol (MSDP)", RFC 3446, January
2003.
20.2. Informative References
[DEPLOY] McBride, M., Meylor, J. and D. Meyer, "Multicast
Source Discovery Protocol (MSDP) Deployment
Scenarios", Work in Progress, July 2003.
[RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:
Keyed-Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2202] Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and
HMAC-SHA-1", RFC 2202, September 1997.
21. Editors’ Addresses
Bill Fenner
AT&T Labs -- Research
75 Willow Road
Menlo Park, CA 94025
EMail: fenner@research.att.com
David Meyer
EMail: dmm@1-4-5.net
22. Full Copyright Statement
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.