Network Working Group Lou Berger Internet Draft FORE Systems, Inc. Expiration Date: September 1999 Der-Hwa Gan Juniper Networks, Inc. George Swallow Cisco Systems, Inc. March 1999 RSVP Refresh Reduction Extensions draft-berger-rsvp-refresh-reduct-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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." To view the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in an Internet-Drafts Shadow Directory, see http://www.ietf.org/shadow.html. Abstract This document describes a number of mechanisms that reduce the refresh overhead of RSVP. The extensions can be used to reduce processing requirements of refresh messages, eliminate the state synchronization latency incurred when an RSVP message is lost and, when desired, suppress the generation of refresh messages. An extension to support detection of when an RSVP neighbor resets its state is also defined. These extension present no backwards compatibility issues. Berger, et al. [Page 1] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 Contents 1 Introduction and Background ............................ 3 2 RSVP Aggregate Message ................................. 4 2.1 Aggregate Header ....................................... 4 2.2 Message Formats ........................................ 5 2.3 Sending RSVP Aggregate Messages ........................ 6 2.4 Receiving RSVP Aggregate Messages ...................... 7 2.5 Forwarding RSVP Aggregate Messages ..................... 7 2.6 Aggregate-Capable Bit .................................. 7 3 MESSAGE_ID Extension ................................... 8 3.1 MESSAGE_ID Object ...................................... 9 3.2 Ack Message Format ..................................... 10 3.3 MESSAGE_ID Object Usage ................................ 10 3.4 MESSAGE_ID ACK Object Usage ............................ 12 3.5 Multicast Considerations ............................... 13 3.6 Compatibility .......................................... 14 4 Hello Extension ........................................ 15 4.1 Hello Message Format ................................... 16 4.2 HELLO Object ........................................... 16 4.3 Hello Message Usage .................................... 17 4.4 Compatibility .......................................... 17 5 Acknowledgments ........................................ 18 6 Security Considerations ................................ 18 7 References ............................................. 18 8 Authors' Addresses ..................................... 18 Berger, et al. [Page 2] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 1. Introduction and Background The extensions described in this document were motivated by MPLS traffic engineering requirements as described in [Awduche]. These extensions may be generally useful and may be supported independent of other MPLS related RSVP extensions or LSP tunnels. The resource requirements (in terms of cpu processing and memory) for running RSVP on a router increases proportionally with the number of sessions. Supporting a large number of sessions can present scaling problems. This document describes mechanisms to help alleviate one set of scaling issues. RSVP Path and Resv messages must be periodically refreshed to maintain state. The approach described effectively reduces the volume of messages which must be periodically sent and received. The described mechanisms also address issues of latency and reliability of RSVP Signaling. The latency and reliability problem occurs when a non-refresh RSVP message is lost in transmission. Standard RSVP [RFC2205] maintains state via the generation of RSVP refresh messages. In the face of transmission loss of RSVP messages, the end-to-end latency of RSVP signaling is tied to the refresh interval of the node(s) experiencing the loss. When end-to-end signaling is limited by the refresh interval, the establishment or change of a reservation may be beyond the range of what is acceptable for some applications. One way to address the refresh volume problem is to increase the refresh timer R. Increasing the value of R provides linear improvement on transmission overhead, but at the cost of increasing refresh timeout. One way to address the latency and reliability of RSVP Signaling is to decrease the refresh timer R. Decreasing the value of R provides increased probability that state will be installed in the face of message loss, but at the cost of increasing refresh message rate and associated processing requirements. The extensions defined in this document address both the refresh volume and the reliability issues with mechanisms other than adjusting refresh rate. An aggregate message is defined to reduce overall message handing load. A Message_ID object is defined to reduce refresh message processing by allowing the receiver to more readily identify an unchanged message. A Message_ACK object is defined which can be used to detect message loss and, when used in combination with the Message_ID object, can be used to suppress Berger, et al. [Page 3] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 refresh messages altogether. Finally, a hello protocol is defined to allow detection of the loss of a neighbor node or a reset of it's RSVP state information. 2. RSVP Aggregate Message An RSVP aggregate message consists of an aggregate header followed by a body consisting of a variable number of standard RSVP messages. The following subsections define the formats of the aggregate header and the rules for including standard RSVP messages as part of the message. 2.1. Aggregate Header 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vers | Flags | Msg type | RSVP checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Send_TTL | (Reserved) | RSVP length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the aggregate header is identical to the format of the RSVP common header [RFC2205]. The fields in the header are as follows: Vers: 4 bits Protocol version number. This is version 1. Flags: 4 bits 0x01: Aggregate capable If set, indicates to RSVP neighbors that this node is willing and capable of receiving aggregate messages. This bit is meaningful only between adjacent RSVP neighbors. 0x02-0x08: Reserved Msg type: 8 bits 12 = Aggregate Berger, et al. [Page 4] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 RSVP checksum: 16 bits The one's complement of the one's complement sum of the entire message, with the checksum field replaced by zero for the pur- pose of computing the checksum. An all-zero value means that no checksum was transmitted. Because individual sub-messages carry their own checksum as well as the INTEGRITY object for authentication, this field MAY be set to zero. Send_TTL: 8 bits The IP TTL value with which the message was sent. This is used by RSVP to detect a non-RSVP hop by comparing the IP TTL that an Aggregate message sent to the TTL in the received message. RSVP length: 16 bits The total length of this RSVP aggregate message in bytes, in- cluding the aggregate header and the sub-messages that follow. 2.2. Message Formats An RSVP aggregate message must contain at least one sub-message. A sub-message is one of the RSVP Path, PathTear, PathErr, Resv, ResvTear, ResvErr, ResvConf, Ack or Hello messages. Empty RSVP aggregate messages should not be sent. It is illegal to include another RSVP aggregate message as a sub-message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vers | Flags | 12 | RSVP checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Send_TTL | (Reserved) | RSVP length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // First sub-message // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // More sub-messages.. // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Berger, et al. [Page 5] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 2.3. Sending RSVP Aggregate Messages RSVP Aggregate messages are sent hop by hop between RSVP-capable neighbors as "raw" IP datagrams with protocol number 46. Raw IP datagrams are also intended to be used between an end system and the first/last hop router, although it is also possible to encapsulate RSVP messages as UDP datagrams for end-system communication that cannot perform raw network I/O. RSVP Aggregate messages MUST not be used if the next hop RSVP neighbor does not support RSVP Aggregate messages. Methods for discovering such information include: (1) manual configuration and (2) observing the Aggregate-capable bit (see the description that follows) in the received RSVP messages. Support for RSVP Aggregate messages is optional. While message aggregation helps in scaling RSVP, and in reducing processing overhead and bandwidth consumption, a node is not required to transmit every standard RSVP message in an Aggregate message. A node MUST always be ready to receive standard RSVP messages. The IP source address is local to the system that originated the Aggregate message. The IP destination address is the next hop node for which the sub-messages are intended. These addresses need not be identical to those used if the sub-messages were sent as standard RSVP messages. For example, the IP source address of Path and PathTear messages is the address of the sender it describes, while the IP destination address is the DestAddress for the session. These end-to-end addresses are overridden by hop-by-hop addresses while encapsulated in an Aggregate message. These addresses can easily be restored from the SENDER_TEMPLATE and SESSION objects within Path and PathTear messages. For Path and PathTear messages, the next hop node can be identified either via a received ACK or from a received corresponding Resv message. Path and PathTear messages for multicast sessions MUST NOT be sent in Aggregate messages. RSVP Aggregate messages SHOULD NOT be sent with the Router Alert IP option in their IP headers. This is because Aggregate messages are addressed directly to RSVP neighbors. Each RSVP Aggregate message MUST occupy exactly one IP datagram. If it exceeds the MTU, the datagram is fragmented by IP and reassembled at the recipient node. A single RSVP Aggregate message MUST NOT exceed the maximum IP datagram size, which is approximately 64K bytes. Berger, et al. [Page 6] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 2.4. Receiving RSVP Aggregate Messages If the local system does not recognize or does not wish to accept an Aggregate message, the received messages shall be discarded without further analysis. The receiver next compares the IP TTL with which an Aggregate message is sent to the TTL with which it is received. If a non-RSVP hop is detected, the number of non-RSVP hops is recorded. It is used later in processing of sub-messages. Next, the receiver verifies the version number and checksum of the RSVP aggregate message and discards the message if any mismatch is found. The receiver then starts decapsulating individual sub-messages. Each sub-message has its own complete message length and authentication information. Each sub-message is processed per standard RSVP. 2.5. Forwarding RSVP Aggregate Messages When an RSVP router receives an Aggregate messages which is not addressed to one of it's IP addresses, it SHALL forward the message. Non-RSVP routers will treat RSVP Aggregate messages as any other IP datagram. When individual sub-messages are being forwarded, they MAY be encapsulated in another aggregate message before sending to the next hop neighbor. The Send_TTL field in the sub-messages should be decremented properly before transmission. 2.6. Aggregate-Capable Bit To support message aggregation, an additional capability bit is added to the common RSVP header, which is defined in [RFC2205]. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vers | Flags | Msg Type | RSVP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Send_TTL | (Reserved) | RSVP Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Berger, et al. [Page 7] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 Flags: 4 bits 0x01: Aggregate capable If set, indicates to RSVP neighbors that this node is willing and capable of receiving aggregate messages. This bit is meaningful only between adjacent RSVP neighbors. 3. MESSAGE_ID Extension Two new objects are defined as part of the MESSAGE_ID extension. The two object types are the MESSAGE_ID object and the MESSAGE_ID ACK object. The objects are used to support acknowledgments and, when used in conjunction with the Hello Extension described in Section 4, to indicate when refresh messages are not needed after an acknowledgment. When refreshes are normally generated, the MESSAGE_ID object can also be used to simply provide a shorthand indication of when a message represents new state. Such information can be used on the receiving node to reduce refresh processing requirements. Message identification and acknowledgment is done on a hop-by-hop basis. Acknowledgment is handled independent of SESSION or message type. Both types of MESSAGE_ID objects contain a message identifier. The identifier MUST be unique on a per source IP address basis across messages sent by an RSVP node and received by a particular node. No more than one MESSAGE_ID object may be included in an RSVP message. Each message containing an MESSAGE_ID object may be acknowledged via a MESSAGE_ID ACK object. MESSAGE_ID ACK objects may be sent piggybacked in unrelated RSVP messages or in RSVP ACK messages Either type of MESSAGE_ID object may be included in an aggregate sub-message. When included, the object is treated as if it were contained in a standard, unaggregated, RSVP message. Only one MESSAGE_ID object MAY be included in a (sub)message and it MUST follow any present MESSAGE_ID ACK objects. When no MESSAGE_ID ACK objects are present, the MESSAGE_ID object MUST immediately follow the INTEGRITY object. When no INTEGRITY object is present, the MESSAGE_ID object MUST immediately follow the (sub)message header. When present, one or more MESSAGE_ID ACK objects MUST immediately follow the INTEGRITY object. When no INTEGRITY object is present, the MESSAGE_ID ACK objects MUST immediately follow the the (sub)message header. An MESSAGE_ID ACK object may only be included in a message when the message's IP destination address matches the unicast address of the node that generated the message(s) being acknowledged. Berger, et al. [Page 8] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 3.1. MESSAGE_ID Object MESSAGE_ID Class = 166 (Value to be assigned by IANA of form 10bbbbbb) MESSAGE_ID object Class = MESSAGE_ID Class, C_Type = 1 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags: 8 bits 0x80 = ACK_Desired flag Indicates that the sender is willing to accept a message acknowledgment. Acknowledgments MUST be silently ignored when they are sent in response to messages whose ACK_Desired flag is not set. This flag MUST be set when the Last_Refresh flag is set. 0x40 = Last_Refresh flag Used in Resv and Path refresh messages to indicate that the sender will not be sending further refreshes. When set, the ACK_Desired flag MUST also be set. This flag MUST NOT be set when the HELLO messages are not being exchanged with the neighboring RSVP node. Message ID: 24 bits a 24-bit identifier. When combined with the message generator's IP address, uniquely identifies a message. MESSAGE_ID ACK object Class = MESSAGE_ID Class, C_Type = 2 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Berger, et al. [Page 9] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 Reserved This field is reserved. It MUST be set to zero on transmis- sion and MUST be ignored on receipt. Message ID: 24 bits a 24-bit identifier. When combined with the message generator's IP address, uniquely identifies a message. 3.2. Ack Message Format Ack messages carry one or more MESSAGE_ID ACK objects. They MUST NOT contain any MESSAGE_ID objects. Ack messages are sent hop-by-hop between RSVP nodes. The IP destination address of an Ack message is the unicast address of the node that generated the message(s) being acknowledged. For Path, PathTear, Resv, and RervErr messages this is taken from the RSVP_HOP Object. For PathErr and ResvErr messages this is taken from the message's source address. The IP source address is an address of the node that sends the Ack message. The Ack message format is as follows: ::= [ ] [ ... ] For Ack messages, the Msg Type field of the Common Header MUST be set to 13 (Value to be assigned by IANA). 3.3. MESSAGE_ID Object Usage The MESSAGE_ID object may be included in any RSVP message other than the Ack message. The MESSAGE_ID object is always generated and processed hop-by-hop. The IP address of the object generator is represented in a per RSVP message type specific fashion. For Path and PathTear messages the generator's IP address is contained in the RSVP_HOP. For Resv, ResvTear, PathErr, ResvErr, ResvConf and Aggregate messages the generator's IP address is the source address in the IP header. The Message ID field contains a generator selected value. This value, when combined with the generator's IP address, identifies a particular RSVP message and the specific state information it represents. When a node is sending a refresh message with a MESSAGE_ID object, it SHOULD use the same Message ID value that was Berger, et al. [Page 10] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 used in the RSVP message that first advertised the state being refreshed. When a node is sending a message that represents new or changed state, the Message ID value MUST have a value that is not otherwise in use. A value is considered to be in use when it has been used in the most recent advertisement or refresh of any state using the associated IP address. Care must also be taken to avoid reuse of a previously used value during times of network loss. At such times, the use of new values may not be noticed by receivers. There is no requirement for Message ID values to be increasing or ordered. The ACK_Desired flag is set when the MESSAGE_ID object generator is capable of accepting MESSAGE_ID ACK objects. Such information can be used to ensure reliable delivery of error and confirm messages and to support fast refreshes in the face of network loss. Nodes setting the ACK_Desired flag SHOULD retransmit unacknowledged messages at a faster interval than the standard refresh time until the message is acknowledged or a "fast" retry limit is reached. Note that nodes setting the ACK_Desired flag for unicast sessions, do not need to track the identify of the next hop since all that is expected is an ACK, not an ACK from a specific next hop. Issues relate to multicast sessions are covered in a later section. The Last_Refresh flag may be set in Path and Resv messages when the MESSAGE_ID object generator is exchanging Hello messages, described in Section 4, with the next hop RSVP node. When a refresh message with the Last_Refresh flag set is generated, normal refresh generation MUST continue until the message containing the Last_Refresh flag is acknowledged. Although, messages removing state advertised in such messages MUST be retransmit until acknowledged or a maximum retry limit is reached in order to cover certain packet loss conditions. Messages removing state include PathTear and ResvTear. When sending MESSAGE_ID objects with the Last_Refresh flag set, special care must be taken to properly advertise state. Specifically, refresh processing MUST continue per standard RSVP processing until after a acknowledgment is received. Suppression of refresh processing MAY ONLY occur after an acknowledgment is received for a MESSAGE_ID object with the Last_Refresh flag set. Note that the Last_Refresh flag MAY ONLY be set when the RSVP next hop is exchanging Hello messages with the message generator. When a Path message for a new session arrives, the RSVP next hop may not always be known. When the RSVP next hop is not known, the Last_Refresh flag MUST NOT be set. Once the next hop of a unicast session is identified, only then may the Last_Refresh flag be set. (Issues relate to multicast sessions are covered in a later section.) Berger, et al. [Page 11] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 There are several ways to identify the RSVP next hop of a new unicast session. Some are more conservative than other, e.g., waiting for a Resv message versus checking if the other end of a PPP link supports Hello messages. Since there are no interoperability issues, the specific mechanism used to identify the RSVP next hop of a new session is a specific implementation choice. In most implementations, it is expected that an advertiser of Path state will do standard refresh processing until either an ACK is received for a Path message advertising a new session, or a corresponding Resv message is received. Nodes receiving messages containing MESSAGE_ID objects SHOULD use the information in the objects to aid in determining if a message represents new state or a state refresh. Note that state is only refreshed in Path and Resv messages. If a Path or Resv message contains the same Message_ID value that was used in the most recently received message for the same session and, for Path messages, SENDER_TEMPLATE then the receiver SHOULD treat the message as a state refresh. If the Message ID value differs from the most recently received value, the receiver MUST fully processes the message. Nodes receiving a message containing a MESSAGE_ID object with the ACK_Desired flag set, SHOULD respond with a MESSAGE_ID ACK object. If a node supports the Hello extension it MUST also check the Last_Refresh flag of received Resv and Path messages. If the flag is set, the receiver MUST NOT timeout state associated with associated message. The receiver MUST also be prepared to properly process refresh messages. Messages containing a MESSAGE_ID ACK object with the Last_Refresh flag set MUST NOT be acknowledged when either the receiving node doesn't support the Hello extension or Hello messages aren't being exchanged with the message generator. 3.4. MESSAGE_ID ACK Object Usage The MESSAGE_ID ACK object is used to acknowledge receipt of messages containing MESSAGE_ID objects that were sent with the ACK_Desired flag set. The Message ID field of a MESSAGE_ID ACK object MUST have the same value as was received. A MESSAGE_ID ACK object MUST NOT be generated in response to a received MESSAGE_ID object when the ACK_Desired flag is not set. A MESSAGE_ID ACK object MAY be sent in any RSVP message that has an IP destination address matching the generator of the associated MESSAGE_ID object. The MESSAGE_ID ACK object will not typically be included in the non hop-by-hop Path, PathTear and ResvConf messages. When no appropriate message is available, one or more MESSAGE_ID ACK objects SHOULD be sent in an Ack message. Implementations SHOULD Berger, et al. [Page 12] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 include MESSAGE_ID ACK objects in standard RSVP messages when possible. Upon receiving a MESSAGE_ID ACK object for a message generated with a MESSAGE_ID object with the Last_Refresh flag set, normal refresh generation SHOULD be suppressed for the associated state. As previously mentioned, special care must be taken to properly advertise state when sending MESSAGE_ID objects with the Last_Refresh flag set, see section 3.3. 3.5. Multicast Considerations Path and PathTear messages may be sent to IP multicast destination addresses. When the destination is a multicast address, it is possible that a single message containing a single MESSAGE_ID object will be received by multiple RSVP next hops. When the ACK_Desired flag is set in this case, acknowledgment processing is more complex. There are a number of issues to be addressed including ACK implosion, number acknowledgments to be expected and handling of new receivers. ACK implosion occurs when each receiver responds to the MESSAGE_ID object at approximately the same time. This can lead to a potentially large number of MESSAGE_ID ACK objects being simultaneously delivered to the message generator. To address this case, the receiver MUST wait a random interval prior to acknowledging a MESSAGE_ID object received in a message destined to a multicast address. The random interval SHOULD be between zero (0) and a configured maximum time. The configured maximum SHOULD be set in proportion to the refresh and "fast" retransmission interval. A more fundamental issue is the number of acknowledgments that the upstream node, i.e., the message generator, should expect. The number of acknowledgments that should be expected is the same as the number of RSVP next hops. In the router-to-router case, the number of next hops can usually be obtained from routing. When hosts are either the upstream node or the next hops, the number of next hops will typically not be readily available. When the number of next hops is not known, the message generator SHOULD only expect a single response and MUST NOT set the Last_Refresh flag in MESSAGE_ID objects. The result of this behavior will be special retransmission handling until the message is delivered to at least one next hop, then followed by standard RSVP refreshes. Standard refresh messages will synchronize state with any next hops that don't receive the original message. Another issue is handling new receivers. It is possible that after sending a Path message and handling of expected number of Berger, et al. [Page 13] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 acknowledgments that a new receiver joins the group. In this case a new Path message must be sent to the new receiver. When normal refresh processing is occurring, there is no issue. When normal refresh processing is suppressed, a Path message must still be generated. In the router-to-router case, the identification of new next hops can usually be obtained from routing. When hosts are either the upstream node or the next hops, the identification of new next hops will typically not be possible. When identification of new next hops is not possible, the message generator SHOULD only expect a single response and MUST NOT set the Last_Refresh flag in MESSAGE_ID objects. The result of this behavior will be special retransmission handling until the message is delivered to at least one next hop, then followed by standard RSVP refreshes. Standard refresh messages will synchronize state with any next hops that don't receive the original message either due to loss or not yet being a group member. There is one additional minor issue with multiple next hops. The issue is handling a combination of standard-refresh and non-refresh next hops, i.e., Hello messages are being exchanged with some neighboring nodes but not with others. When this case occurs, refreshes MUST be generated per standard RSVP and the Last_Refresh flag MUST NOT be set. 3.6. Compatibility There are no backward compatibility issues raised by the MESSAGE_ID Class. The MESSAGE_ID Class has an assigned value whose form is 10bbbbbb. Per RSVP [RFC2205], classes with values of this form must be ignored and not forwarded by nodes not supporting the class. When the receiver of a MESSAGE_ID object does not support the class, the object will be silently ignored. The generator of the MESSAGE_ID object will not see any acknowledgments and therefore refresh messages per standard RSVP. Lastly, since the MESSAGE_ID ACK object can only be issued in response to the MESSAGE_ID object, there are no possible issues with this object or Ack messages. Implementations supporting Path and Resv state refresh suppression via the MESSAGE_ID object's Last_Refresh flag MUST also support the Hello extension. Berger, et al. [Page 14] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 4. Hello Extension The RSVP Hello extension enables RSVP nodes to detect a loss of a neighboring node's state information. In standard RSVP, such detection occurs as a consequence of RSVP's soft state model. When refresh message generation is suppressed via the previously discussed Last_Refresh flag processing, the Hello extension is needed to address this failure case. The Hello extensions is not intended to provide a link failure detection mechanism, particularly in the case of multiple parallel unnumbered links. The Hello extension is specifically designed so that one side can use the mechanism while the other side does not. Neighbor RSVP state tracking may be initiated at any time. This includes when neighbors first learn about each other, or just when neighbors are sharing Resv or Path state. As previously stated, all implementations supporting state refresh suppression MUST also support the Hello Extension. Such implementations SHOULD initiate Hello processing and MUST be able to respond to Hello messages. The Hello extension is composed of a Hello message, a HELLO REQUEST object and a HELLO ACK object. Hello processing between two neighbors supports independent selection of, typically configured, failure detection intervals. Each neighbor can autonomously issue HELLO REQUEST objects. Each request is answered by an acknowledgment. Hello Messages also contain enough information so that one neighbor can suppress issuing hello requests and still perform neighbor failure detection. A Hello message may be included as a sub-message within an aggregate message. Neighbor state tracking is accomplished by collecting and storing a neighbor's state "instance" value. If a change in value is seen, then the neighbor is presumed to have reset it's RSVP state. The HELLO objects provide a mechanism for polling for and providing an RSVP state instance value. A poll request also includes the sender's instance value. This allows the receiver of a poll to optionally treat the poll as an implicit poll response. This optional handling is an optimization that can reduce the total number of polls and responses processed by a pair of neighbors. In all cases, when both sides support the optimization the result will be only one set of polls and responses per failure detection interval. Depending on selected intervals, the same benefit can occur even when only one neighbor supports the optimization. Berger, et al. [Page 15] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 4.1. Hello Message Format Hello Messages are always sent between two RSVP neighbors. The IP source address is the IP address of the sending node. The IP destination address is the IP address of the neighbor node. The Hello message format is as follows: ::= [ ] For Hello messages, the Msg Type field of the Common Header MUST be set to 14 (Value to be assigned by IANA). 4.2. HELLO Object HELLO Class = 22 (Value to be assigned by IANA of form 0bbbbbbb) HELLO REQUEST object Class = HELLO Class, C_Type = 1 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Instance | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ HELLO ACK object Class = HELLO Class, C_Type = 2 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Instance | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Instance: 32 bits a 32 bit value that represents the sender's RSVP agent's state. This value must change when the agent is reset or the node reboots and otherwise remains the same. This field MUST NOT be set to zero (0). Berger, et al. [Page 16] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 4.3. Hello Message Usage A Hello message containing a HELLO REQUEST object MUST be generated for each neighbor who's state is being tracked. When generating a message containing a HELLO REQUEST object, the sender fills in the Instance field with a value representing it's RSVP agent state. This value MUST NOT change while the agent is maintaining any RSVP state. The generation of a message SHOULD be skipped when a HELLO REQUEST object was received from the destination node within the failure detection interval. On receipt of a message containing a HELLO REQUEST object, the receiver MUST generate a Hello message containing a HELLO ACK object. The receiver SHOULD also verify that the neighbor has not reset. This is done by comparing the sender's Instance field value with the previously received value. If the value differs, than the neighbor has reset and all state associated with the neighbor MUST be "expired" and cleaned up per standard RSVP processing. Additionally, all Path state advertised to the neighbor MUST be refreshed. On receipt of a message containing a HELLO ACK object, the receiver MUST verify that the neighbor has not reset. This is done by comparing the sender's Instance field value with the previously received value. If the value differs, than the neighbor has reset and all state associated with the neighbor MUST be "expired" and cleaned up per standard RSVP processing. Additionally, all Path state advertised to the neighbor MUST be refreshed. 4.4. Compatibility The Hello extension is fully backwards compatible. The Hello class is assigned a class value of the form 0bbbbbbb. Depending on the implementation, implementations that don't support the extension will either silently discard Hello messages or will respond with an "Unknown Object Class" error. In either case the sender will fail to see an acknowledgment for the issued Hello. When a Hello sender does not receive an acknowledgment, it MUST NOT send MESSAGE_ID objects with the Last_Refresh flag set. This restriction will preclude neighbors from getting out of RSVP state synchronization. Implementations supporting the Hello extension MUST also support the MESSAGE_ID extension and refresh suppression. Berger, et al. [Page 17] Internet Draft draft-berger-rsvp-refresh-reduct-00.txt March 1999 5. Acknowledgments This document represents ideas and comments from the MPLS-TE design team. Thanks to Yoram Bernet and Fred Baker for the good feedback. 6. Security Considerations No new security issues are raised in this document. See [RFC2205] for a general discussion on RSVP security issues. 7. References [Awduche] Awduche, D. et al. Requirements for Traffic Engineering over MPLS, Internet Draft, draft-awduche-mpls-traffic-eng-00.txt, April 1998. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119. [RFC2205] Braden, R. Ed. et al, "Resource ReserVation Protocol -- Version 1 Functional Specification", RFC 2205, September 1997. 8. Authors' Addresses Lou Berger FORE Systems 1595 Spring Hill Road, Suite 500 Vienna, VA 22182 Voice: +1 703 245 4527 Email: lberger@fore.com Der-Hwa Gan Juniper Networks, Inc. 385 Ravendale Drive Mountain View, CA 94043 Voice: +1 650 526 8074 Email: dhg@juniper.net George Swallow Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA 01824 Voice: +1 978 244 8143 Email: swallow@cisco.com Berger, et al. [Page 18]