Network Working Group Dino Farinacci INTERNET DRAFT Procket Networks Yakov Rekhter David Meyer Cisco Systems Peter Lothberg Sprint Hank Kilmer Jeremy Hall UUnet Category Standards Track December, 1999 Multicast Source Discovery Protocol (MSDP) 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. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 1] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 2. Abstract The Multicast Source Discovery Protocol, MSDP, describes a mechanism to connect multiple PIM-SM domains together. Each PIM-SM domain uses it's own independent RP(s) and does not have to depend on RPs in other domains. 3. Copyright Notice Copyright (C) The Internet Society (1999). 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. o Global Source State Global source state is not required, since a router need not cache Source Active (SA) messages (see below). MSDP is a periodic protocol. 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]. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 2] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 5. Overview An RP (or other MSDP SA originator) in a PIM-SM [RFC2362] domain will have a MSDP peering relationship with a MSDP speaker in another domain. The peering relationship will be made up of a TCP connection in which control information exchanged. Each domain will have one or more connections to this virtual topology. The purpose of this topology is to have domains 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 speakers can be realized by the underlying BGP routing system. 6. Procedure A source in a PIM-SM domain originates traffic to a multicast group. The PIM DR which is directly connected to the source sends the data encapsulated in a PIM Register message to the RP in the domain. The RP will construct a "Source-Active" (SA) message and send 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. 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 BGP routing table is examined to determine which peer is the NEXT_HOP towards the originating RP of the SA message. Such a peer is called an "RPF peer". See section 10 below for the details of peer-RPF fowarding. 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 it's MSDP peers. The flooding can be further constrained to children of the peer by interrogating BGP reachability information. That is, if a BGP peer advertises a route (back to you) and you are the next to last AS in the AS_PATH, the peer is using you as the NEXT_HOP. In this case, an Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 3] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 implementation SHOULD forward an SA message (which was originated from the RP address covered by that route) to the peer. This is known in other circles as Split-Horizon with Poison Reverse. When an MSDP peer which is also an RP for its own domain receives an 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 (See [RFC2362] Section 3.2.2). 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, and it is caching SAs, then 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. 7. Controlling State While RPs which receive SA messages are not required to keep MSDP (S,G) state, an RP SHOULD cache SA messages by default. The advantage of caching is that newly formed MSDP peers can get MSDP (S,G) state sooner and therefore reduce join latency for new joiners. In addition, caching greatly aids in diagnosis and debugging of various problems. 7.1. Timers The main timers for MSDP are: SA Advertisement period, SA Hold-down period, the SA Cache timeout period, KeepAlive, HoldTimer, and ConnectRetry. Each is described below. 7.1.1. SA Advertisement Period RPs which originate SA messages do it periodically as long as there is data being sent by the source. The SA Advertisement Period MUST be 60 seconds. An RP will not send more than one SA message for a given (S,G) within an SA Advertisement period. Originating periodic SA Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 4] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 messages is important so that new receivers who join after a source has been active can get data quickly via the receiver's own RP when it is not caching SA state. Finally, if an RP in a domain receives a PIM Join message for a new group G, and it is caching SAs, then the RP should trigger a (S,G) join for each SA for that group in its cache. 7.1.2. SA Hold-down Period A caching MSDP speaker SHOULD NOT forward an SA message it has received in the last SA-Hold-down period. The SA-Hold-down period SHOULD be set to 30 seconds. 7.1.3. SA Cache Timeout A caching MSDP speaker times out it's SA cache at SA-State-Timer. The SA-State-Timer MUST NOT be less than 90 seconds. 7.1.4. KeepAlive, HoldTimer, and ConnectRetry The KeepAlive, HoldTimer, and ConnectRetry timers are defined in RFC 1771 [RFC1771]. 7.2. Intermediate MSDP Speakers Intermediate RPs do not originate periodic SA messages on behalf of sources in other domains. In general, an RP MUST only originate an SA for its own sources. 7.3. 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, hoever, 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 black holes). In general, policy should be expressed using MBGP [RFC2283]. This will cause MSDP messages will 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) Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 5] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 MUST NOT be sent to peers which are on the other side of an administrative scope boundary for G. 7.4. SA Requests If an MSDP peer decides to cache SA state, it may accept SA-Requests from other MSDP peers. When an MSDP peer 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 sending to the group range requested in the SA-Request message. The peer that sends the request will not flood the responding SA-Response message to other peers. If an implementation receives an SA-Request message and is not caching SA messages, it sends a notification with Error code 7 subcode 1, as defined in section 12.2.7. 8. Encapsulated Data Packets For bursty sources, 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 number of packets from the source which 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. Finally, if an implementation supports an encapsulation of SA data other than default TCP encapsulation, then it MUST support GRE encapsulation. In addition, an implementation MUST learn about not TCP encapsulations via capability advertisement (see section 11.2.5). Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 6] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 9. 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 different 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. Another example is the Anycast RP mechanism [ANYCASTRP]. 10. 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. 10.1. Peer-RPF Forwarding Rules An SA message originated by an MSDP originator R and received by a MSDP router from MSDP peer N is accepted if N is the appropriate RPF neighbor for originator R. The RPF neighbor is chosen using the first of the following rules that matches: (i). R is the RPF neighbor if we have an MSDP peering with R. (ii). The external MBGP neighbor towards which we are poison-reversing the MBGP route towards R is the RPF neighbor if we have an MSDP peering with it. (iii). If we have an MSDP peering with a neighbor in the first AS along the AS_PATH (the AS from which we learned this route), but no exeternal MBGP peering with that neighbor, pick a neighbor via a deterministic rule if you have have several, and that is the RPF neighbor. (vi). The internal MBGP advertiser of the router towards R is the RPF neighbor if we have an MSDP peering with it. (v). If none of the above match, and we have an MSDP default-peer configured, the MSDP default-peer is the RPF neighbor. Once an RPF neighbor is chosen (as defined above), an SA message is accepted if it was received from the RPF neighbor, and discarded otherwise. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 7] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 10.2. MSDP default-peer semantics A MSDP default-peer is much like a default route. It is intended to be used in those cases where a stub network isn't running BGP or MBGP. A MSDP speaker configured with a default-peer accepts all SA messages from the default-peer. Note that a router running BGP or MBGP SHOULD NOT allow configuration of default peers, since this allows the possibility for SA looping to occur. 11. MSDP Connection Establishment MSDP speakers establish peering sessions according to the following state machine: Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 8] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 De-configured or disabled +-------------------------------------------+ | | +-----|--------->+----------+ | | | +->| INACTIVE |----------------+ | | | | +----------+ | | Deconf'ed | | | /|\ /|\ | Timer + Higher Address or | | | | | | | disabled | | | | | \|/ | | | | | | | +-------------+ | | | | | +---------------| CONNECTING | | | | | | Timeout or +-------------+ | | | | | Router ID Change | \|/ \|/ | | | | +----------+ | | | | | DISABLED | | | +---------------------+ | TCP Established +----------+ | | | | /|\ /|\ | | Connection Timeout or | | | | | | Router ID change or | | | | | | Authorization Failure | | | | | | | | | | | | | \|/ | | | | +-------------+ | | Router ID | | Timer + | ESTABLISHED | | | Change | | Low Address +-------------+ | | | \|/ /|\ | | | | +--------+ | | | | +--| LISTEN |--------------------+ | | | +--------+ TCP Accept | | | | | | | | | | +---------------+ | | De-configured or | | disabled | | | +------------------------------------------------------+ De-configured or disabled Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 9] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 12. Packet Formats MSDP messages will be encapsulated in a TCP connection using well- known port 639. One side of the MSDP peering relationship will listen on the well-known port and the other side will do an active connect on the well-known port. The side with the higher peer IP address will do the 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 end. Finally, 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. 12.1. MSDP messages will be encoded in TLV format: 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. The minimum length required is 3 octets. Value (variable length) Format is based on the Type value. See below. The length of the value field is Length field minus 3. 12.2. 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 Encapsulation Capability Advertisement 6 Encapsulation Capability Request 7 Notification Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 10] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 8 GRE Encapsulation Each TLV is described below. 12.2.1. IPv4 Source-Active TLV The maximum size SA message that can be sent is 1400 bytes. If an MSDP peer needs to originate a message with information greater than 1400 bytes, it sends successive 1400-byte messages. The 1400 byte size does not include the TCP, IP, layer-2 headers. 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 | Gprefix Len | Sprefix Len | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ | Group Address Prefix | ) z +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / | Source Address Prefix | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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 Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 11] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 The address of the RP in the domain the source has become active in. Reserved The Reserved field MUST be transmitted as zeros and ignored by a receiver. Gprefix Len and Sprefix Len The route prefix length associated with the group address prefix and source address prefix, respectively. Group Address Prefix The group address the active source has sent data to. Source Address Prefix The route prefix associated with 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. 12.2.2. IPv4 Source-Active Request TLV The Source-Active Request is used to request SA-state from a caching 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, and it has been configured to peer with an SA-state caching peer, it may send an SA-Request message for the group. 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 | Gprefix Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type IPv4 Source-Active Request TLV is type 2. Gprefix Len The route prefix length associated with the group address prefix. Group Address Prefix The group address prefix the MSDP peer is requesting. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 12] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 12.2.3. 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 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. 12.2.4. KeepAlive TLV A KeepAlive TLV is sent to an MSDP peer if and only if there were no MSDP messages sent to the peer after a period of time. This message is necessary for the active connect side of the MSDP connection. The passive connect side of the connection knows that the connection will be reestablished when a TCP SYN packet is sent from the active connect side. However, the active connect side will not know when the passive connect side goes down. Therefore, the KeepAlive timeout will be used to reset the TCP connection. 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 bytes which encompasses the 1-byte Type field and the 2-byte Length field. 12.2.5. Encapsulation Capability Advertisement TLV This TLV is sent by an MSDP speaker to advertise its ability to receive data packets encapsulated as described by the TLV (in addition to the default TCP encapsulation). A MSDP speaker receiving this TLV can choose to either default TCP Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 13] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 encapsulation, or may send a IPv4 Encapsulation Request to change to the advertised encapsulation type. 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 | 8 | ENCAP_TYPE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type IPv4 Encapsulation Advertisement TLV is type 5. Length Length is a two byte field with value 8. ENCAP_TYPE The following data encapsulation types are defined for MSDP: Value Meaning --------------------------------------- 0 TCP Encapsulation 1 UDP Encapsulation [RFC768] 2 GRE Encapsulation [GRE] Source Port Port for use by the requester. Reserved The Reserved field MUST be transmitted as zeros and ignored by a receiver. Note that since the TLV does not carry endpoint addresses for the GRE or UDP tunnels, an implementation using these encapsulations MUST use the endpoints that are used for the MSDP peering. 12.2.6. Encapsulation Capability Request TLV The Encapsulation Capability Request is sent to notify a peer that has advertised an encapsulation capability that it will encapsulate SA data according to the advertised ENCAP_TYPE. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 6 | 4 | ENCAP_TYPE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 14] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 Type IPv4 Encapsulation Request TLV is type 6. Length Length is a two byte field with value 4. ENCAP_TYPE ENCAP_TYPE is described above. A requester MAY also provide a source port, in which case the TLV has the following form: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 6 | 8 | ENCAP_TYPE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 12.2.7. NOTIFICATION TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 7 | x + 5 | Error Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error subcode | ... | +-+-+-+-+-+-+-+-+ | | Data | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type The Notification TLV is type 7. Length Length is a two byte field with value x + 5, where x is the length of the notification data field. Error code See [RFC1771]. In addition, Error code 7 indicates an an SA-Request Error. Error subcode See [RFC1771]. In addition, Error code 7 subcode 1 indicates the receipt of an SA-Request message by a non-caching MSDP speaker. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 15] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 Data See [RFC1771]. In addition, for Error code 7 subcode 1 (receipt of an SA-Request message by a non-caching MSDP speaker), the TLV has the following form: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 7 | 20 | 7 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | Reserved | Gprefix Len | Sprefix Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising RP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address Prefix | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ See [RFC1771] for NOTIFICATION error handling. 12.2.8. Encapsulation Capability State Machine The active connect side of an MSDP peering SHALL begin in ADVERTISING state, and the passive side of the TCP connection begins in DEFAULT state. This will cause the state machine to behave deterministically. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 16] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 +-------+ | | Receive TLV which isn't | | understood or | | Receive Request (TLV 6) or | | Receive Advertisement (TLV 5) \|/ | that isn't understood +---------+----+ | DEFAULT |----------------+ +---------+ | | +-------------+ | | ADVERTISING | | +-------------+ | | | Timeout +--------+ | | +-------->| FAILED | | Send Advertisement | Receive Advertisement | +--------+ | (TLV 5) | (TLV 5) | | | | | | | | | | | | | Receive non-matching | | | Request (TLV 6) | | | +----+ | | | | | | | | | | | | | | \|/ | \|/ | | +------+ | +----------+ | +-| SENT |<-------------+ | RECEIVED | +---+------+ +----------+ | \|/ | | | Receive matching | Send matching | Request (TLV 6) | Request (TLV 6) | +--------+ | +------------>| AGREED |<------------------+ +--------+ Note that if an advertiser transitions into the FAILED state, it SHOULD assume that it has an old-style peer which can only support TCP encapsulation. If an implementation wishes to be backwardly compatible, it SHOULD support TCP encapsulation. In addition, a requester in any state other than AGREED MUST only encapsulate data in the TCP stream. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 17] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 12.2.9. UDP Data Encapsulation When using UDP encapsulation, the UDP psuedo-header has the following form: 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 | Dest Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Origin RP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Source Port When using UDP encapsulation, a capability requester uses the advertiser's Source Port as its destination port. The advertiser MUST provide a Source Port. Destination Port When using UDP encapsulation, a capability advertiser uses the well known port 639 as the destination port. A capability requester MUST listen on this well-known port. The requester MAY provide a Source Port in it's reply to the advertiser. Length Length is the length in octets of this user datagram including this header and the data. The minimum value of the length is twelve. 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. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 18] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 12.2.10. GRE Encapsulation TLV A TLV is defined to describe GRE encapsulated data packets. The TLV has the following form: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 8 | 8 + x | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Originating RP IPv4 Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (S,G) Data Packet .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type GRE encapsulated data packet TLV is type 8. Length Length is a two byte field with value 8 + x, where x is the length of the (S,G) Data packet. Reserved The Reserved field MUST be transmitted as zeros and ignored by a receiver. The entire GRE header, then, will have the following form: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Delivery Headers ..... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |C| Reserved0 | Ver | Protocol Type |\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GRE Header | Checksum (optional) | Reserved1 |/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\ | 8 | 8 + x | Reserved | \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Payload | Originating RP IPv4 Address | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . | (S,G) Data Packet .... . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 19] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 12.2.10.1. Problems with MTU Exceeded by Encapsulation Black holes can arise when PMTU [RFC1191] is used and the tunnel entry point does not relay MTU exceeded errors back to the originator of the packet. A black hole can be realized by the following behavior: the originator sets the Don't Fragment bit in the Delivery Header, the packet gets dropped within the tunnel (MTU is exceeded), but since the originator doesn't receive feedback, it retransmits with the same PMTU, causing subsequently transmitted packets to be dropped. While GRE [GRE] does not require that such errors be relayed back to the originator, known implementations of GRE do not set the Don't Fragment bit in the Delivery Header. 13. Security Considerations An MSDP implementation MAY use IPsec [RFC1825] or keyed MD5 [RFC1828] to secure control messages. When encapsulating SA data 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. 14. Acknowledgments The authors would like to thank Dave Thaler, Bill Nickless, John Meylor, Liming Wei, Manoj Leelanivas, Mark Turner, and John Zwiebel for their design feedback and comments. Bill Fenner also made many contributions, including clarification of the Peer-RPF rules. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 20] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 15. Author's Address: Dino Farinacci Procket Networks 3850 No. First St., Ste. C San Jose, CA 95134 Email: dino@procket.com Yakov Rehkter Cisco Systems, Inc. 170 Tasman Drive San Jose, CA, 95134 Email: yakov@cisco.com Peter Lothberg Sprint VARESA0104 12502 Sunrise Valley Drive Reston VA, 20196 Email: roll@sprint.net Hank Kilmer Email: hank@rem.com Jeremy Hall UUnet Technologies 3060 Williams Drive Fairfax, VA 22031 Email: jhall@uu.net David Meyer Cisco Systems, Inc. 170 Tasman Drive San Jose, CA, 95134 Email: dmm@cisco.com Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 21] Internet Draft draft-ietf-msdp-spec-01.txt December, 1999 16. REFERENCES [ANYCASTRP] Meyer, et. al, "Anycast RP mechanism using PIM and MSDP", draft-ietf-mboned-anycast-rp-04.txt, November, 1999. Work in Progress. [GRE] Farinacci, D., at el., "Generic Routing Encapsulation (GRE)", draft-meyer-gre-update-01.txt, December, 1999. Work in Progress. [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. [RFC1825] Atkinson, R., "Security Architecture for the Internet Protocol", RFC 1825, August, 1995. [RFC1828] P. Metzger and W. Simpson, "IP Authentication using Keyed MD5", RFC 1828, August, 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. Farinacci, Rekhter, Lothberg, Kilmer, Hall, Meyer [Page 22]