One document matched: draft-berger-rsvp-refresh-reduct-01.txt
Differences from draft-berger-rsvp-refresh-reduct-00.txt
Network Working Group Lou Berger
Internet Draft LabN Consulting
Expiration Date: October 1999
Der-Hwa Gan
Juniper Networks, Inc.
George Swallow
Cisco Systems, Inc.
April 1999
RSVP Refresh Reduction Extensions
draft-berger-rsvp-refresh-reduct-01.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.
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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 ................................... 11
3.4 MESSAGE_ID ACK Object Usage ............................... 13
3.5 Multicast Considerations .................................. 13
3.5.1 Reference RSVP/Routing Interface .......................... 15
3.6 Compatibility ............................................. 15
4 Hello Extension ........................................... 16
4.1 Hello Message Format ...................................... 17
4.2 HELLO Object .............................................. 17
4.3 Hello Message Usage ....................................... 18
4.4 Multi-Link Considerations ................................. 19
4.5 Compatibility ............................................. 19
5 Acknowledgments ........................................... 20
6 Security Considerations ................................... 20
7 References ................................................ 20
8 Authors' Addresses ........................................ 20
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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 scal-
ing 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 reliabil-
ity 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 improve-
ment 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 vol-
ume and the reliability issues with mechanisms other than adjusting
refresh rate. An aggregate message is defined to reduce overall mes-
sage 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 refresh messages
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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 informa-
tion.
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 fol-
lows:
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,
including the aggregate header and the sub-messages that fol-
low.
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 can-
not perform raw network I/O.
RSVP Aggregate messages MUST not be used if the next hop RSVP neigh-
bor does not support RSVP Aggregate messages. Methods for discover-
ing such information include: (1) manual configuration and (2)
observing the Aggregate-capable bit (see the description that fol-
lows) in the received RSVP messages.
Support for RSVP Aggregate messages is optional. While message
aggregation helps in scaling RSVP, and in reducing processing over-
head 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 mes-
sages. 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 encap-
sulated in another aggregate message before sending to the next hop
neighbor. The Send_TTL field in the sub-messages should be decre-
mented 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 acknowledg-
ment. 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 piggy-
backed 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 con-
tained in a standard, unaggregated, RSVP message. Only one MES-
SAGE_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 MES-
SAGE_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)mes-
sage header. An MESSAGE_ID ACK object may only be included in a mes-
sage 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.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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).
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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 pro-
cessed hop-by-hop. The IP address of the object generator is repre-
sented 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 Aggre-
gate 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 repre-
sents. When a node is sending a refresh message with a MESSAGE_ID
object, it SHOULD use the same Message ID value that was 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 genera-
tion 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 condi-
tions. Messages removing state include PathTear and ResvTear.
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When sending MESSAGE_ID objects with the Last_Refresh flag set, spe-
cial 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 process-
ing MAY ONLY occur after an acknowledgment is received for a MES-
SAGE_ID object with the Last_Refresh flag set. Note that the
Last_Refresh flag MAY ONLY be set when the RSVP next hop is exchang-
ing 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.)
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 spe-
cific 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 adver-
tising 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 repre-
sents new state or a state refresh. Note that state is only
refreshed in Path and Resv messages. If a Path or Resv message con-
tains 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.
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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 MES-
SAGE_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
include MESSAGE_ID ACK objects in standard RSVP messages when possi-
ble.
Upon receiving a MESSAGE_ID ACK object for a message generated with a
MESSAGE_ID object with the Last_Refresh flag set, normal refresh gen-
eration 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 possi-
ble 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, num-
ber 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 poten-
tially 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 MES-
SAGE_ID object received in a message destined to a multicast address.
The random interval SHOULD be between zero (0) and a configured maxi-
mum 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
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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. Another case where the num-
ber of RSVP next hops will typically not be known is when there are
non-RSVP routers between the message generator and the RSVP next
hops.
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 deliv-
ered 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 acknowledg-
ments that a new receiver joins the group. In this case a new Path
message must be sent to the new receiver. When normal refresh pro-
cessing is occurring, there is no issue. When normal refresh pro-
cessing 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 typi-
cally not be possible. Another case where the identification of new
RSVP next hops will typically not be possible is when there are non-
RSVP routers between the message generator and the RSVP next hops.
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 deliv-
ered 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 neigh-
boring 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.
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3.5.1. Reference RSVP/Routing Interface
When using the MESSAGE_ID extension with multicast sessions it is
preferable for RSVP to obtain the number of next hops from routing
and to be notified when that number changes. The interface between
routing and RSVP is purely an implementation issue. Since RSVP
[RFC2205] describes a reference routing interface, we present a ver-
sion of the RSVP/routing interface updated to provide number of next
hop information. See [RFC2205] for previously defined parameters and
function description.
o Route Query
Mcast_Route_Query( [ SrcAddress, ] DestAddress,
Notify_flag )
-> [ IncInterface, ] OutInterface_list,
NHops_list
o Route Change Notification
Mcast_Route_Change( ) -> [ SrcAddress, ] DestAddress,
[ IncInterface, ] OutInterface_list,
NHops_list
NHops_list provides the number of multicast group members
reachable via each OutInterface_list entry.
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 mes-
sages 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. Such implementations SHOULD initiate Hello process-
ing and MUST be able to respond to Hello messages.
Berger, et al. [Page 15]
Internet Draft draft-berger-rsvp-refresh-reduct-01.txt April 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 detec-
tion 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 are required to also support the Hello
Extension.
The Hello extension is composed of a Hello message, a HELLO REQUEST
object and a HELLO ACK object. Hello processing between two neigh-
bors 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 fail-
ure 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. When a
neighbor's value is seen to change or when communication is lost with
a neighbor, then the instance value advertised to that neighbor is
also changed. 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 16]
Internet Draft draft-berger-rsvp-refresh-reduct-01.txt April 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 desti-
nation 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.
The advertiser maintains a per neighbor representation/value.
This value MUST change when the agent is reset, when the node
reboots, or when a failure of the neighboring node is detected
and otherwise remains the same. This field MUST NOT be set to
zero (0).
Berger, et al. [Page 17]
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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 per neighbor RSVP agent
state. This value MUST NOT change while the agent is maintaining any
RSVP state with the corresponding neighbor. The generation of a mes-
sage 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. If any
state is removed or needs to be refreshed as a result of detecting a
change in a received Instance field value, then the value advertised
in the HELLO ACK object MUST be be different from the previously
advertised value. This new value MUST continue to be advertised to
the corresponding neighbor until a reset or reboot occurs, or until
another neighbor reset is detected.
On receipt of a message containing a HELLO ACK object, the receiver
MUST verify that the neighbor has not reset. This is done by compar-
ing 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 adver-
tised to the neighbor MUST be refreshed. If any state is removed or
needs to be refreshed as a result of detecting a change in a received
Instance field value, then a new HELLO message MUST be immediately
issued with a value different then the one advertised in the previous
HELLO message. This new value MUST continue to be advertised to the
corresponding neighbor until a reset or reboot occurs, or until
another neighbor reset is detected.
If no Instance value is received, via either REQUEST or ACK objects,
from a neighbor within a configured number of failure detection
intervals, then a node MUST treat the neighbor as if it has reset.
Specifically, all state associated with the neighbor MUST be
"expired" and cleaned up per standard RSVP processing, and all Path
state advertised to the neighbor MUST be refreshed. If any state is
removed or needs to be refreshed as a result of this case, then a new
HELLO message MUST be immediately issued with a value different then
Berger, et al. [Page 18]
Internet Draft draft-berger-rsvp-refresh-reduct-01.txt April 1999
the one advertised in the previous HELLO message. This new value
MUST continue to be advertised to the corresponding neighbor until a
reset or reboot occurs, or until another neighbor reset is detected.
4.4. Multi-Link Considerations
As previously noted, the Hello extension is targeted at detecting
node failures not per link failures. When there is only one link
between neighboring nodes or when all links between a pair of nodes
fail, the distinction between node and link failures is not really
meaningful and handling of such failures has already been covered.
When there are multiple links shared between neighbors, there are
special considerations. When the links between neighbors are num-
bered, then Hellos MUST be run on each link and the previously
described mechanisms apply.
When the links are unnumbered, link failure detection MUST be pro-
vided by some means other than Hellos. Each node SHOULD use a single
Hello exchange with the neighbor. When a node removes state due to a
link failure, the node MUST advertise the removal of the state, via
appropriate Tear messages, over a non-failed link. The case where
all links have failed, is the same as the no received value case men-
tioned in the previous section.
4.5. 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 19]
Internet Draft draft-berger-rsvp-refresh-reduct-01.txt April 1999
5. Acknowledgments
This document represents ideas and comments from the MPLS-TE design
team. Thanks to Yoram Bernet, Fred Baker, Andreas Terzis and David
Mankins 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
LabN Consulting
Voice: +1 301 468 9228
Email: lberger@tidalwave.net
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 20]
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