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
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To view the current status of any Internet-Draft, please check the
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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.
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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
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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
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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
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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.. //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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:
<ACK Message> ::= <Common Header> [ <INTEGRITY> ]
<MESSAGE_ID ACK>
[ <MESSAGE_ID ACK> ... ]
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
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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.)
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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
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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
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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.
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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:
<Hello Message> ::= <Common Header> [ <INTEGRITY> ]
<HELLO>
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]