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IETF RFC 5946
Resource Reservation Protocol (RSVP) Extensions for Path-Triggered RSVP Receiver Proxy
Last modified on Monday, October 11th, 2010
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Internet Engineering Task Force (IETF) F. Le Faucheur
Request for Comments: 5946 Cisco
Updates: 2205 J. Manner
Category: Standards Track Aalto University
ISSN: 2070-1721 A. Narayanan
Cisco
A. Guillou
SFR
H. Malik
Airtel
October 2010
Resource Reservation Protocol (RSVP) Extensions
for Path-Triggered RSVP Receiver Proxy
 Abstract
Resource Reservation Protocol (RSVP) signaling can be used to make
end-to-end resource reservations in an IP network in order to
guarantee the Quality of Service (QoS) required by certain flows.
With conventional RSVP, both the data sender and receiver of a given
flow take part in RSVP signaling. Yet, there are many use cases
where resource reservation is required, but the receiver, the sender,
or both, is not RSVP-capable. Where the receiver is not RSVP-
capable, an RSVP router may behave as an RSVP Receiver Proxy, thereby
performing RSVP signaling on behalf of the receiver. This allows
resource reservations to be established on the segment of the end-to-
end path from the sender to the RSVP Receiver Proxy. However, as
discussed in the companion document "RSVP Proxy Approaches", RSVP
extensions are needed to facilitate operations with an RSVP Receiver
Proxy whose signaling is triggered by receipt of RSVP Path messages
from the sender. This document specifies these extensions.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 5946.
Le Faucheur, et al. Standards Track PAGE 1 
RFC 5946 RSVP Receiver Proxy Extensions October 2010
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Le Faucheur, et al. Standards Track PAGE 2
RFC 5946 RSVP Receiver Proxy Extensions October 2010
Table of Contents
1. Introduction ....................................................4
1.1. Conventions Used in This Document ..........................7
2. Terminology .....................................................7
3. RSVP Extensions for Sender Notification .........................8
3.1. Sender Notification via PathErr Message ...................11
3.1.1. Composition of SESSION and Sender Descriptor .......14
3.1.2. Composition of ERROR_SPEC ..........................14
3.1.3. Use of Path_State_Removed Flag .....................15
3.1.4. Use of PathErr by Regular Receivers ................16
3.2. Sender Notification via Notify Message ....................17
4. Mechanisms for Maximizing the Reservation Span .................23
4.1. Dynamic Discovery of Downstream RSVP Functionality ........24
4.2. Receiver Proxy Control Policy Element .....................26
4.2.1. Default Handling ...................................29
5. Security Considerations ........................................29
5.1. Security Considerations for the Sender
Notification via Notify Message ...........................30
5.2. Security Considerations for the Receiver Proxy
Control Policy Element ....................................31
6. IANA Considerations ............................................32
6.1. RSVP Error Codes ..........................................32
6.2. Policy Element ............................................32
7. Acknowledgments ................................................33
8. References .....................................................33
8.1. Normative References ......................................33
8.2. Informative References ....................................34
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
1. Introduction
Guaranteed Quality of Service (QoS) for some applications with tight
QoS requirements may be achieved by reserving resources in each node
on the end-to-end path. The main IETF protocol for these resource
reservations is the Resource Reservation Protocol (RSVP), as
specified in [RFC 2205]. RSVP does not require that all intermediate
nodes support RSVP, but it assumes that both the sender and the
receiver of the data flow support RSVP. However, there are
environments where it would be useful to be able to reserve resources
for a flow (at least a subset of the flow path) even when the sender
or the receiver (or both) is not RSVP-capable.
Since both the data sender and receiver may be unaware of RSVP, there
are two types of RSVP Proxies. In the first case, an entity in the
network needs to invoke RSVP on behalf of the data sender and thus
generate RSVP Path messages, and eventually receive, process, and
sink Resv messages. We refer to this entity as the RSVP Sender
Proxy. In the second case, an entity in the network needs to operate
RSVP on behalf of the receiver and thus receive Path messages sent by
a data sender (or by an RSVP Sender Proxy), and reply to those with
Resv messages generated on behalf of the data receiver(s). We refer
to this entity as the RSVP Receiver Proxy.
RSVP Proxy approaches are presented in [RFC 5945]. That document also
discusses, for each approach, how the reservations controlled by the
RSVP Proxy can be synchronized with the application requirements
(e.g., when to establish, maintain, and tear down the RSVP
reservation to satisfy application requirements).
One RSVP Proxy approach is referred to as the Path-Triggered RSVP
Receiver Proxy approach. With this approach, the RSVP Receiver Proxy
uses the RSVP Path messages generated by the sender (or RSVP Sender
Proxy) as the cue for establishing the RSVP reservation on behalf of
the non-RSVP-capable receiver(s). The RSVP Receiver Proxy is
effectively acting as an intermediary making reservations (on behalf
of the receiver) under the sender's control (or RSVP Sender Proxy's
control). This somewhat changes the usual RSVP reservation model
where reservations are normally controlled by receivers. Such a
change greatly facilitates operations in the scenario of interest
here, which is where the receiver is not RSVP-capable. Indeed it
allows the RSVP Receiver Proxy to remain application-unaware by
taking advantage of the application awareness and RSVP awareness of
the sender (or RSVP Sender Proxy).
Since the synchronization between an RSVP reservation and an
application is now effectively performed by the sender (or RSVP
Sender Proxy), it is important that the sender (or RSVP Sender Proxy)
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
is aware of the reservation state. However, as conventional RSVP
assumes that the reservation is to be controlled by the receiver,
some notifications about reservation state (notably the error message
sent in the case of admission control rejection of the reservation)
are only sent towards the receiver and therefore, in our case, sunk
by the RSVP Receiver Proxy. Section 3 of this document specifies
extensions to RSVP procedures allowing such notifications to be also
conveyed towards the sender. This facilitates synchronization by the
sender (or RSVP Sender Proxy) between the RSVP reservation and the
application requirements, and it facilitates sender-driven control of
reservation in scenarios involving a Path-Triggered RSVP Receiver
Proxy.
With unicast applications in the presence of RSVP Receiver Proxies,
if the sender is notified about the state of the reservation towards
the receiver (as enabled by this document), the sender is generally
in a good position to synchronize the reservation with the
application and to perform efficient sender-driven reservation: the
sender can control the establishment or removal of the reservation
towards the receiver by sending Path or PathTear messages,
respectively. For example, if the sender is notified that the
reservation for a point-to-point audio session towards the receiver
is rejected, the sender may trigger rejection of the session at the
application layer and may issue a PathTear message to remove any
corresponding RSVP state (e.g., Path states) previously established.
However, we note that multicast applications do not always coexist
well with RSVP Receiver Proxies, since sender notification about
reservation state towards each RSVP Receiver Proxy may not be
sufficient to achieve tight application-level synchronization by
multicast senders. These limitations stem from the fact that
multicast operation is receiver driven and, while end-to-end RSVP is
also receiver driven (precisely to deal with multicast efficiently),
the use of RSVP Receiver Proxies only allows sender-driven
reservation. For example, a sender generally is not aware of which
receivers have joined downstream of a given RSVP Receiver Proxy, or
even which RSVP Receiver Proxies have joined downstream of a given
failure point. Therefore, it may not be possible to support a mode
of operation whereby a given receiver only joins a group if that
receiver benefits from a reservation. Additionally, a sender may
have no recourse if only a subset of RSVP Receiver Proxies return
successful reservations (even if application-level signaling runs
between the sender and receivers), since the sender may not be able
to correctly identify the set of receivers who do not have
reservations. However, it is possible to support a mode of operation
whereby multicast traffic is transmitted if and only if all receivers
benefit from a reservation (from sender to their respective RSVP
Receiver Proxy): the sender can ensure this by sending a PathTear
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
message and stopping transmission whenever it gets a notification for
reservation reject for one or more RSVP Receiver Proxies. It is also
possible to support a mode of operation whereby receivers join
independently of whether or not they can benefit from a reservation
(to their respective RSVP Receiver Proxy), but do benefit from a
reservation whenever the corresponding resources are reservable on
the relevant path.
This document discusses extensions to facilitate operations in the
presence of a Path-Triggered RSVP Receiver Proxy. As pointed out
previously, those apply equally whether RSVP signaling is initiated
by a regular RSVP sender or by an RSVP Sender Proxy (with some means
to synchronize reservation state with application-level requirements
that are outside the scope of this document). For readability, the
rest of this document discusses operations assuming a regular RSVP
sender; however, such an operation is equally applicable where an
RSVP Sender Proxy is used to initiated RSVP signaling on behalf of a
non-RSVP-capable sender.
As discussed in [RFC 5945], it is important to keep in mind that the
strongly recommended RSVP deployment model remains end to end as
assumed in [RFC 2205] with RSVP support on the sender and the
receiver. The end-to-end model allows the most effective
synchronization between the reservation and application requirements.
Also, when compared to the end-to-end RSVP model, the use of RSVP
Proxies involves additional operational burden and/or imposes some
topological constraints. Thus, the purpose of this document is only
to allow RSVP deployment in special environments where RSVP just
cannot be used on some senders and/or some receivers for reasons
specific to the environment.
Section 4.1.1 of [RFC 5945] discusses mechanisms allowing the RSVP
reservation for a given flow to be dynamically extended downstream of
an RSVP Proxy whenever possible (i.e., when the receiver is RSVP-
capable or when there is another RSVP Receiver Proxy downstream).
This can considerably alleviate the operational burden and the
topological constraints associated with Path-Triggered RSVP Receiver
Proxies. This allows (without corresponding manual configuration) an
RSVP reservation to dynamically span as much of the corresponding
flow path as possible, with any arbitrary number of RSVP Receiver
Proxies on the flow path and whether or not the receiver is RSVP-
capable. In turn, this facilitates migration from an RSVP deployment
model based on Path-Triggered Receiver Proxies to an end-to-end RSVP
model, since receivers can gradually and independently be upgraded to
support RSVP and then instantaneously benefit from end-to-end
reservations. Section 4 of this document specifies these mechanisms
and associated RSVP extensions.
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
2. Terminology
The following terminology is borrowed from [RFC 5945] and is used
extensively in this document:
o RSVP-capable (or RSVP-aware): supporting the RSVP protocol as per
[RFC 2205].
o RSVP Receiver Proxy: an RSVP-capable router performing, on behalf
of a receiver, the RSVP operations that would normally be
performed by an RSVP-capable receiver if end-to-end RSVP signaling
were used. Note that while RSVP is used upstream of the RSVP
Receiver Proxy, RSVP is not used downstream of the RSVP Receiver
Proxy.
o RSVP Sender Proxy: an RSVP-capable router performing, on behalf of
a sender, the RSVP operations that normally would be performed by
an RSVP-capable sender if end-to-end RSVP signaling were used.
Note that while RSVP is used downstream of the RSVP Sender Proxy,
RSVP is not used upstream of the RSVP Sender Proxy.
o Regular RSVP Router: an RSVP-capable router that is not behaving
as an RSVP Receiver Proxy nor as an RSVP Sender Proxy.
Note that the roles of the RSVP Receiver Proxy, RSVP Sender Proxy,
and regular RSVP Router are all relative to one unidirectional flow.
A given router may act as the RSVP Receiver Proxy for a flow, as the
RSVP Sender Proxy for another flow, and as a regular RSVP router for
yet another flow.
The following terminology is also used in this document:
o Regular RSVP sender: an RSVP-capable host behaving as the sender
for the considered flow and participating in RSVP signaling in
accordance with the sender behavior specified in [RFC 2205].
o Regular RSVP receiver: an RSVP-capable host behaving as the
receiver for the considered flow and participating in RSVP
signaling in accordance with the receiver behavior specified in
[RFC 2205].
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
3. RSVP Extensions for Sender Notification
This section defines extensions to RSVP procedures allowing sender
notification of reservation failure. This facilitates
synchronization by the sender between RSVP reservation and
application requirements in scenarios involving a Path-Triggered RSVP
Receiver Proxy.
As discussed in [RFC 5945], with the Path-Triggered RSVP Receiver
Proxy approach, the RSVP router may be configured to use receipt of a
regular RSVP Path message as the trigger for RSVP Receiver Proxy
behavior. On receipt of the RSVP Path message, the RSVP Receiver
Proxy:
1. establishes the RSVP Path state as per regular RSVP processing.
2. identifies the downstream interface towards the receiver.
3. sinks the Path message.
4. behaves as if a corresponding Resv message (on its way upstream
from the receiver) was received on the downstream interface.
This includes performing admission control on the downstream
interface, establishing a Resv state (in the case of successful
admission control), and forwarding the Resv message upstream,
sending periodic refreshes of the Resv message and tearing down
the reservation if the Path state is torn down.
Operation of the Path-Triggered Receiver Proxy in the case of a
successful reservation is illustrated in Figure 1.
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** *** *** |**********| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|****| *** *** *** | Receiver | |----|
| Proxy |
|**********|
--Path---> --Path---> --Path---> --Path--->
<---Resv-- <---Resv-- <---Resv-- <---Resv--
===================RSVP===================>
************************************************************>
|****| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|****| |----| *** router
***> media flow
==> segment of flow path benefiting from an RSVP reservation
Figure 1: Successful Reservation
We observe that, in the case of successful reservation, conventional
RSVP procedures ensure that the sender is notified of the successful
reservation establishment. Thus, no extensions are required in the
presence of a Path-Triggered RSVP Receiver Proxy in the case of
successful reservation establishment.
However, in the case of reservation failure, conventional RSVP
procedures ensure only that the receiver (or the RSVP Receiver Proxy)
is notified of the reservation failure. Specifically, in the case of
an admission control rejection on a regular RSVP router, a ResvErr
message is sent downstream towards the receiver. In the presence of
an RSVP Receiver Proxy, if we simply follow conventional RSVP
procedures, this means that the RSVP Receiver Proxy is notified of
the reservation failure, but the sender is not. Operation of the
Path-Triggered RSVP Receiver Proxy in the case of an admission
control failure, assuming conventional RSVP procedures, is
illustrated in Figure 2.
Le Faucheur, et al. Standards Track PAGE 9
RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** *** *** |**********| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|****| *** *** *** | Receiver | |----|
| Proxy |
|**********|
--Path---> --Path---> --Path---> --Path--->
<---Resv-- <---Resv--
-ResvErr-> -ResvErr->
===================RSVP===================>
************************************************************>
|****| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|****| |----| *** router
***> media flow
==> segment of flow path benefiting from an RSVP reservation
Figure 2: Reservation Failure with Conventional RSVP
While the sender could infer reservation failure from the fact that
it has not received a Resv message after a certain time, there are
clear benefits to ensuring that the sender gets a prompt, explicit
notification in the case of reservation failure. This includes
faster end-user notification at the application layer (e.g., busy
signal) and faster application-level reaction (e.g., application-
level rerouting), as well as faster release of application-level
resources.
Section 3.1 defines a method that can be used to achieve sender
notification of reservation failure. A router implementation
claiming compliance with this document MUST support the method
defined in Section 3.1.
Section 3.2 defines another method that can be used to achieve sender
notification of reservation failure. A router implementation
claiming compliance with this document MAY support the method defined
in Section 3.2.
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
In a given network environment, a network administrator may elect to
use the method defined in Section 3.1, the method defined in
Section 3.2, or possibly combine the two.
3.1. Sender Notification via PathErr Message
With this method, the RSVP Receiver Proxy MUST generate a PathErr
message whenever the two following conditions are met:
1. The reservation establishment has failed (or the previously
established reservation has been torn down).
2. The RSVP Receiver Proxy determines that it cannot re-establish
the reservation (e.g., by adapting its reservation request in
reaction to the error code provided in the received ResvErr in
accordance with local policy).
Note that this notion of generating a PathErr message upstream in
order to notify the sender about a reservation failure is not
completely new. It is borrowed from [RFC 3209] where it was
introduced in order to satisfy a similar requirement, which is to
allow an MPLS Traffic Engineering (TE) Label Switching Router to
notify the TE Tunnel head-end (i.e., the sender) of a failure to
establish (or maintain) a TE Tunnel Label Switch Path.
Operation of the Path-Triggered RSVP Receiver Proxy in the case of an
admission control failure, using sender notification via a PathErr
message, is illustrated in Figure 3.
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** *** *** |**********| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|****| *** *** *** | Receiver | |----|
| Proxy |
|**********|
--Path---> --Path---> --Path---> --Path--->
<---Resv-- <---Resv--
-ResvErr-> -ResvErr->
<-PathErr- <-PathErr- <-PathErr- <-PathErr-
===================RSVP===================>
************************************************************>
|****| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|****| |----| *** router
***> media flow
==> segment of flow path benefiting from RSVP
(but not benefiting from a reservation in this case)
Figure 3: Reservation Failure with Sender Notification via PathErr
The role of this PathErr is to notify the sender that the reservation
was not established or was torn down. This may be in the case of
receipt of a ResvErr, or because of local failure on the Receiver
Proxy. On receipt of a ResvErr, in all situations where the
reservation cannot be installed, the Receiver Proxy MUST generate a
PathErr towards the sender. For local failures on the Receiver Proxy
node, if a similar failure on an RSVP midpoint would cause the
generation of a ResvErr (for example, admission control failure), the
Receiver Proxy MUST generate a PathErr towards the sender. The
Receiver Proxy MAY additionally generate a PathErr upon local
failures that would not ordinarily cause generation of a ResvErr
message, such as those described in Appendix B of [RFC 2205].
The PathErr generated by the Receiver Proxy corresponds to the
sender(s) that triggered generation of Resv messages that failed.
For FF-style (Fixed-Filter) reservations, the Receiver Proxy MUST
send a PathErr towards the (single) sender matching the failed
reservation. For SE-style (Shared-Explicit) reservations, the
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
Receiver Proxy MUST send the PathErr(s) towards the set of senders
that triggered reservations that failed. This may be a subset of
senders sharing the same reservation, in which case the remaining
senders would have their reservation intact and would not receive a
PathErr. In both cases, the rules described in Section 3.1.8 of
[RFC 2205] for generating flow descriptors in ResvErr messages also
apply when generating sender descriptors in PathErr messages.
For WF-style (Wildcard-Filter) reservations, it is not always
possible for the Receiver Proxy to reliably know which sender caused
the reservation failure. Therefore, the Receiver Proxy SHOULD send a
PathErr towards each sender. This means that all the senders will
receive a notification that the reservation is not established,
including senders that did not cause the reservation failure.
Therefore, the method of sender notification via a PathErr message is
somewhat overly conservative (i.e., in some cases, rejecting
reservations from some senders when those could have actually been
established) when used in combination with the Wildcard-Filter style
(and when there is more than one sender).
The sender notification via the PathErr method applies to both
unicast and multicast sessions. However, for a multicast session, it
is possible that reservation failure (e.g., admission control
failure) in a node close to a sender may cause ResvErr messages to be
sent to a large group of Receiver Proxies. These Receiver Proxies
would, in turn, all send PathErr messages back to the same sender,
which could cause a scalability issue in some environments.
From the perspective of the sender, errors that prevent a reservation
from being set up can be classified in two ways:
1. Errors that the sender can attempt to correct. The error code
for these errors should explicitly be communicated back to the
sender. An example of this is "Code 1: Admission Control
Failure", because the sender could potentially resend a Path
message with smaller traffic parameters.
2. Errors over which the sender has no control. For these errors,
it is sufficient to notify the sender that the reservation was
not set up successfully. An example of this is "Code 13: Unknown
Object", because the sender has no control over the objects
inserted into the reservation by the Receiver Proxy.
The PathErr message generated by the Receiver Proxy has the same
format as regular PathErr messages defined in [RFC 2205]. The
SESSION, ERROR_SPEC, and sender descriptor are composed by the
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
Receiver Proxy as specified in the following subsections. The
Receiver Proxy MAY reflect back towards the sender in the PathErr any
POLICY_DATA objects received in the ResvErr.
3.1.1. Composition of SESSION and Sender Descriptor
The Receiver Proxy MUST insert the SESSION object corresponding to
the failed reservation into the PathErr. For FF-style reservations,
the Receiver Proxy MUST insert a sender descriptor corresponding to
the failed reservation into the PathErr. This is equal to the error
flow descriptor in the ResvErr received by the Receiver Proxy. For
SE-style reservations, the Receiver Proxy MUST insert a sender
descriptor corresponding to the sender triggering the failed
reservation into the PathErr. This is equal to the error flow
descriptor in the ResvErr received by the Receiver Proxy. If
multiple flow descriptors could not be admitted at a midpoint node,
that node would generate multiple ResvErr messages towards the
receiver as per Section 3.1.8 of [RFC 2205]. Each ResvErr would
contain an error flow descriptor that matches a specific sender. The
Receiver Proxy MUST generate a PathErr for each ResvErr received
towards the corresponding sender. As specified earlier, for WF-style
reservations, the Receiver Proxy SHOULD send a PathErr to each
sender.
3.1.2. Composition of ERROR_SPEC
The Receiver Proxy MUST compose the ERROR_SPEC to be inserted into
the PathErr as follows:
1. If the Receiver Proxy receives a ResvErr with either of these
error codes -- "Code 1: Admission Control Failure" or "Code 2:
Policy Control Failure" -- then the Receiver Proxy copies the
error code and value from the ERROR_SPEC in the ResvErr into the
ERROR_SPEC of the PathErr message. The error node in the PathErr
MUST be set to the address of the Receiver Proxy. This procedure
MUST also be followed for a local error on the Receiver Proxy
that would ordinarily cause a midpoint to generate a ResvErr with
one of the above codes.
2. If the Receiver Proxy receives a ResvErr with any error code
except the ones listed in item 1 above, it composes a new
ERROR_SPEC with error code "36: Unrecoverable Receiver Proxy
Error". The error node address in the PathErr MUST be set to the
address of the Receiver Proxy. This procedure MUST also be
followed for a local error on the Receiver Proxy that would
ordinarily cause a midpoint to generate a ResvErr with any error
code other than those listed in item 1 above, or if the Receiver
Proxy generates a PathErr for a local error that ordinarily would
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
not cause generation of a ResvErr. In some cases, it may be
predetermined that the PathErr will not reach the sender. For
example, a node receiving a ResvErr with "Code 3: No Path for
Resv", knows a priori that the PathErr message it generates
cannot be forwarded by the same node that could not process the
Resv. Nevertheless, the procedures above MUST be followed. For
the error code "36: Unrecoverable Receiver Proxy Error", the 16
bits of the Error Value field are:
* hhhh hhhh llll llll
where the bits are:
* hhhh hhhh = 0000 0000: then the low order 8 bits (llll llll)
MUST be set by Receiver Proxy to 0000 0000 and MUST be ignored
by the sender.
* hhhh hhhh = 0000 0001: then the low order 8 bits (llll llll)
MUST be set by the Receiver Proxy to the value of the error
code received in the ResvErr ERROR_SPEC (or, in case the
Receiver Proxy generated the PathErr without having received a
ResvErr, to the error code value that would have been included
by the Receiver Proxy in the ERROR_SPEC in similar conditions
if it was to generate a ResvErr). This error value MAY be
used by the sender to further interpret the reason for the
reservation failure.
* hhhh hhhh = any other value: reserved.
3. If the Receiver Proxy receives a ResvErr with the InPlace flag
set in the ERROR_SPEC, it MUST also set the InPlace flag in the
ERROR_SPEC of the PathErr.
3.1.3. Use of Path_State_Removed Flag
[RFC 3473] defines an optional behavior whereby a node forwarding a
PathErr message can remove the Path state associated with the PathErr
message and indicate so by including the Path_State_Removed flag in
the ERROR_SPEC object of the PathErr message. This can be used in
some situations to expedite release of resources and minimize
signaling load.
This section discusses aspects of the use of the Path_State_Removed
flag that are specific to the RSVP Receiver Proxy. In any other
aspects, the Path_State_Removed flag operates as per [RFC 3473].
Le Faucheur, et al. Standards Track PAGE 15
RFC 5946 RSVP Receiver Proxy Extensions October 2010
By default, the RSVP Receiver Proxy MUST NOT include the
Path_State_Removed flag in the ERROR_SPEC of the PathErr message.
This ensures predictable operations in all environments including
those where some RSVP routers do not understand the
Path_State_Removed flag.
The RSVP Receiver Proxy MAY support an OPTIONAL mode (to be activated
by configuration) whereby the RSVP Receiver Proxy includes the
Path_State_Removed flag in the ERROR_SPEC of the PathErr message and
removes its local Path state. When all routers on the path of a
reservation support the Path_State_Removed flag, its use will indeed
result in expedited resource release and reduced signaling. However,
if there are one or more RSVP routers on the path of the reservation
that do not support the Path_State_Removed flag (we refer to such
routers as "old RSVP routers"), the use of the Path_State_Removed
flag will actually result in slower resource release and increased
signaling. This is because the Path_State_Removed flag will be
propagated upstream by an old RSVP router (even if it does not
understand it and does not tear its Path state). Thus, the sender
will not send a Path Tear, and the old RSVP router will release its
Path state only through refresh time-out. A network administrator
needs to keep these considerations in mind when deciding whether to
activate the use of the Path_State_Removed flag on the RSVP Receiver
Proxy. In a controlled environment where all routers are known to
support the Path_State_Removed flag, its use can be safely activated
on the RSVP Receiver Proxy. In other environments, the network
administrator needs to assess whether the improvement achieved with
some reservations outweighs the degradation experienced by other
reservations.
3.1.4. Use of PathErr by Regular Receivers
Note that while this document specifies that an RSVP Receiver Proxy
generates a PathErr upstream in the case of reservation failure, this
document does NOT propose that the same be done by regular receivers.
In other words, this document does NOT propose modifying the behavior
of regular receivers as currently specified in [RFC 2205]. The
rationale for this includes the following:
o When the receiver is RSVP-capable, the current receiver-driven
model of [RFC 2205] is fully applicable because the receiver can
synchronize RSVP reservation state and application state (since it
participates in both). The sender(s) need not be aware of the
RSVP reservation state. Thus, we can retain the benefits of
receiver-driven operations that were explicitly sought by
[RFC 2205], which states, "In order to efficiently accommodate
large groups, dynamic group membership, and heterogeneous receiver
requirements, RSVP makes receivers responsible for requesting a
Le Faucheur, et al. Standards Track PAGE 16
RFC 5946 RSVP Receiver Proxy Extensions October 2010
specific QoS". But even for the simplest single_sender/
single_receiver reservations, the current receiver-driven model
reduces signaling load and per-hop RSVP processing by not sending
any error message to the sender in case of admission control
reject.
o The motivation for adding sender error notification in the case of
an RSVP Receiver Proxy lies in the fact that the actual receiver
can no longer synchronize the RSVP reservation with application
state (since the receiver does not participate in RSVP signaling),
while the sender can. This motivation does not apply in the case
of a regular receiver.
o There is a lot of existing code and deployed systems successfully
working under the current [RFC 2205] model in the absence of proxy
today. The current behavior of existing deployed systems should
not be changed unless there were a very strong motivation.
3.2. Sender Notification via Notify Message
The OPTIONAL method for sender notification of reservation failure
defined in this section aims to provide a more efficient method than
the one defined in Section 3.1. Its objectives include:
o allowing the failure notification to be sent directly upstream to
the sender by the router where the failure occurs (as opposed to
first traveling downstream towards the Receiver Proxy and then
traveling upstream from the Receiver Proxy to the sender, as
effectively happens with the method defined in Section 3.1).
o allowing the failure notification to travel without hop-by-hop
RSVP processing.
o ensuring that such a notification is sent to senders that are
capable and willing to process it (i.e., to synchronize
reservation status with application).
o ensuring that such a notification is only sent in case the
receiver is not itself capable and willing to do the
synchronization with the application (i.e., because we are in the
presence of a Receiver Proxy so that RSVP signaling is not visible
to the receiver).
Note, however, that such benefits come at the cost of:
o a requirement for RSVP routers and senders to support the Notify
messages and procedures defined in [RFC 3473].
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
o a requirement for senders to process Notify messages traveling
upstream but conveying a downstream notification.
[RFC 3473] defines (in Section 4.3, "Notify Messages") the Notify
message that provides a mechanism to inform non-adjacent nodes of
events related to the RSVP reservation. The Notify message differs
from the error messages defined in [RFC 2205] (i.e., PathErr and
ResvErr messages) in that it can be "targeted" to a node other than
the immediate upstream or downstream neighbor and that it is a
generalized notification mechanism. Notify messages are normally
generated only after a Notify Request object has been received.
This section discusses aspects of the use of the Notify message that
are specific to the RSVP Receiver Proxy. In any other aspects, the
Notify message operates as per [RFC 3473].
In order to achieve sender notification of reservation failure in the
context of this document:
o An RSVP sender interested in being notified of reservation failure
MUST include a Notify Request object (containing the sender's IP
address) in the Path messages it generates.
o Upon receiving a Path message with a Notify Request object, the
RSVP Receiver Proxy MUST include a Notify Request object in the
Resv messages it generates. This Notify Request object MUST
contain either:
* the address that was included in the Notify Request of the
received Path message, a.k.a. the sender's address. We refer
to this approach as the "Direct Notify" approach, or
* an address of the Receiver Proxy. We refer to this approach as
the "Indirect Notify" approach.
o Upon receiving a downstream error notification (whether in the
form of a Notify, ResvErr, or both), the RSVP Receiver Proxy:
* MUST generate a Notify message with upstream notification to
the corresponding sender, if the sender included a Notify
Request object in its Path messages and if Indirect
Notification is used.
* SHOULD generate a Notify message with upstream notification to
the corresponding sender, if the sender included a Notify
Request object in its Path messages and if Direct Notification
is used. The reason for this recommendation is that the
failure node may not support Notify, so that even if Direct
Le Faucheur, et al. Standards Track PAGE 18
RFC 5946 RSVP Receiver Proxy Extensions October 2010
Notification was requested by the RSVP Receiver Proxy, the
sender may not actually have received a Notify from the failure
node: generating a Notify from the Receiver Proxy will
accelerate sender notification, as compared to simply relying
on PathErr, in this situation. In controlled environments
where all the nodes are known to support Notify, the Receiver
Proxy MAY be configured to not generate the Notify with
upstream notification when Direct Notification is used, in
order to avoid duplication of Notify messages (i.e., the sender
receiving both a Notify from the failure node and from the
Receiver Proxy).
As a result of these sender and Receiver Proxy behaviors, as per
existing Notify procedures, if an RSVP router detects an error
relating to a Resv state (e.g., admission control rejection after IP
reroute), the RSVP router will send a Notify message (conveying the
downstream notification with the ResvErr error code) to the IP
address contained in the Resv Notify Request object. If this address
has been set by the RSVP Receiver Proxy to the sender's address
(Direct Notify), the Notify message is sent directly to the sender.
If this address has been set by the RSVP Receiver Proxy to one of its
own addresses (Indirect Notify), the Notify message is sent to the
RSVP Receiver Proxy that, in turn, will generate a Notify message
directly addressed to the sender.
Operation of the Path-Triggered RSVP Receiver Proxy in the case of an
admission control failure, using sender notification via Direct
Notify, is illustrated in Figure 4.
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** *** *** |**********| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|****| *** *** *** | Receiver | |----|
| Proxy |
|**********|
--Path*--> --Path*--> --Path*--> --Path*-->
<--Resv*-- <--Resv*--
<------NotifyD--------
-ResvErr-> -ResvErr->
<------------------NotifyU------------------
<-PathErr- <-PathErr- <-PathErr- <-PathErr-
===================RSVP===================>
************************************************************>
|****| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|****| |----| *** router
***> media flow
==> segment of flow path benefiting from RSVP
(but not benefiting from a reservation in this case)
Path* = Path message containing a Notify Request object
with sender IP Address
Resv* = Resv message containing a Notify Request object
with sender IP address
NotifyD = Notify message containing a downstream notification
NotifyU = Notify message containing an upstream notification
Figure 4: Reservation Failure with Sender Notification
via Direct Notify
Operation of the Path-Triggered RSVP Receiver Proxy in the case of an
admission control failure, using sender notification via Indirect
Notify, is illustrated in Figure 5.
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** *** *** |**********| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|****| *** *** *** | Receiver | |----|
| Proxy |
|**********|
--Path*--> --Path*--> --Path*--> --Path*-->
<--Resv*-- <--Resv*--
-------NotifyD------->
<------------------NotifyU------------------
-ResvErr-> -ResvErr->
<-PathErr- <-PathErr- <-PathErr- <-PathErr-
===================RSVP===================>
************************************************************>
|****| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|****| |----| *** router
***> media flow
==> segment of flow path benefiting from RSVP
(but not benefiting from a reservation in this case)
Path* = Path message containing a Notify Request object
with sender IP Address
Resv* = Resv message containing a Notify Request object
with RSVP Receiver Proxy IP address
NotifyD = Notify message containing a downstream notification
NotifyU = Notify message containing an upstream notification
Figure 5: Reservation Failure with Sender Notification
via Indirect Notify
For local failures on the Receiver Proxy node, if a similar failure
on an RSVP midpoint would cause the generation of a ResvErr (for
example, admission control failure), the Receiver Proxy MUST generate
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RFC 5946 RSVP Receiver Proxy Extensions October 2010
a Notify towards the sender. The Receiver Proxy MAY additionally
generate a Notify upon local failures that would not ordinarily cause
generation of a ResvErr message, such as those described in
Appendix B of [RFC 2205].
When the method of sender notification via a Notify message is used,
it is RECOMMENDED that the RSVP Receiver Proxy also issue a sender
notification via a PathErr message. This maximizes the chances that
the notification will reach the sender in all situations (e.g., even
if some RSVP routers do not support the Notify procedure, or if a
Notify message gets dropped). However, for controlled environments
(e.g., where all RSVP routers are known to support Notify procedures)
and where it is desirable to minimize the volume of signaling, the
RSVP Receiver Proxy MAY rely exclusively on sender notification via a
Notify message and thus not issue sender notification via a PathErr
message.
In environments where there are both RSVP-capable receivers and RSVP
Receiver Proxies acting on behalf of non-RSVP-capable receivers, a
sender does not know whether a given reservation is established with
an RSVP-capable receiver or with an RSVP Receiver Proxy. Thus, a
sender that supports the procedures defined in this section may
include a Notify Request object in Path messages for a reservation
that happens to be controlled by an RSVP-capable receiver. This
document does not define, nor expect, any change in existing receiver
behavior. As a result, in this case, the sender will not receive
Notify messages conveying downstream notifications. However, this is
perfectly fine because the synchronization between the RSVP
reservation state and the application requirement can be performed by
the actual receiver in this case as per the regular end-to-end RSVP
model, so that in this case, the sender need not care about
downstream notifications.
A sender that does not support the procedures defined in this section
might include a Notify Request object in Path messages for a
reservation simply because it is interested in getting upstream
notifications faster. If the reservation is controlled by an RSVP
Receiver Proxy supporting the procedures defined in this section, the
sender will also receive unexpected Notify messages containing
downstream notifications. It is expected that such a sender will
simply naturally drop such downstream notifications as invalid.
Because it is RECOMMENDED above that the RSVP Receiver Proxy also
issue a sender notification via a PathErr message even when sender
notification is effected via a Notify message, the sender will still
be notified of a reservation failure in accordance with the "sender
notification via PathErr" method. In summary, activating the
OPTIONAL "sender notification via Notify" method on a Receiver Proxy
does not prevent a sender that does not support this method from
Le Faucheur, et al. Standards Track PAGE 22
RFC 5946 RSVP Receiver Proxy Extensions October 2010
relying on the MANDATORY "sender notification via PathErr" method.
It would, however, allow a sender supporting the "sender notification
via Notify" method to take advantage of this OPTIONAL method.
With Direct Notification, the downstream notification generated by
the RSVP router where the failure occurs is sent to the IP address
contained in the Notification Request Object of the corresponding
Resv message. In the presence of multiple senders towards the same
session, it cannot be generally assumed that a separate Resv message
is used for each sender (in fact, with WF and SE there is a single
Resv message for all senders, and with FF the downstream router has
the choice of generating separate Resv messages or a single one).
Hence, in the presence of multiple senders, Direct Notification
cannot guarantee notification of all affected senders. Therefore,
Direct Notification is better suited to single-sender applications.
With Indirect Notification, the RSVP Receiver Proxy can generate
Notify messages with the same logic that is used to generate PathErr
messages in the "Sender Notification via PathErr" method (in fact,
those are conveying the same error information, only the Notify is
directly addressed to the sender while the PathErr travels hop-by-
hop). Therefore, operations of the Indirect Notify method in the
presence of multiple senders is similar to that of the PathErr method
as discussed in Section 3.1: with FF or SE, a Notify MUST be sent to
the sender or the set of affected senders, respectively. With WF,
the RSVP Receiver Proxy SHOULD send a Notify to each sender, again
resulting in a somewhat overly conservative behavior in the presence
of multiple senders.
4. Mechanisms for Maximizing the Reservation Span
This section defines extensions to RSVP procedures allowing an RSVP
reservation to span as much of the flow path as possible, with any
arbitrary number of RSVP Receiver Proxies on the flow path and
whether or not the receiver is RSVP-capable. This facilitates
deployment and operations of Path-Triggered RSVP Receiver Proxies
since it alleviates the topological constraints and/or configuration
load otherwise associated with Receiver Proxies (e.g., make sure
there is no RSVP Receiver Proxy for a flow upstream of a given
Receiver Proxy, ensure there is no Receiver Proxy for a flow if the
receiver is RSVP-capable). This also facilitates migration from an
RSVP deployment model based on Path-Triggered Receiver Proxies to an
end-to-end RSVP model, since receivers can gradually and
independently be upgraded to support RSVP and then instantaneously
benefit from end-to-end reservations.
Le Faucheur, et al. Standards Track PAGE 23
RFC 5946 RSVP Receiver Proxy Extensions October 2010
Section 4.1 defines a method that allows a Path-Triggered Receiver
Proxy function to discover whether there is another Receiver Proxy or
an RSVP-capable receiver downstream and then dynamically extend the
span of the RSVP reservation downstream. A router implementation
claiming compliance with this document SHOULD support the method
defined in Section 4.1.
Section 4.2 defines a method that allows a sender to control whether
or not an RSVP router supporting the Path-Triggered Receiver Proxy
function is to behave as a Receiver Proxy for a given flow. A router
implementation claiming compliance with this document MAY support the
method defined in Section 4.2.
In a given network environment, a network administrator may elect to
use the method defined in Section 4.1, or the method defined in
Section 4.2, or possibly combine the two.
4.1. Dynamic Discovery of Downstream RSVP Functionality
When generating a proxy Resv message upstream, a Receiver Proxy
supporting dynamic discovery of downstream RSVP functionality MUST
forward the Path message downstream instead of terminating it (unless
dynamic discovery of downstream RSVP functionality is explicitly
disabled). If the destination endpoint supports RSVP (or there is
another Receiver Proxy downstream), it will receive the Path and
generate a Resv upstream. When this Resv message reaches the
Receiver Proxy, it recognizes the presence of an RSVP-capable
receiver (or of another RSVP Receiver Proxy) downstream and MUST
internally convert its state from a proxied reservation to a regular
midpoint RSVP behavior. From then on, the RSVP router MUST behave as
a regular RSVP router for that reservation (i.e., as if the RSVP
router never behaved as an RSVP Receiver Proxy for that flow). This
method is illustrated in Figure 6.
Le Faucheur, et al. Standards Track PAGE 24
RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** |**********| |----|
| S |---------*r*---------| RSVP |---| R1 |
|****| *** | Receiver | |----|
| Proxy |
| |
| | |****|
| |------------| R2 |
|**********| |****|
---Path---> --Path--->
(R1) (R1) \-------Path-->
/ (R1)
<--Resv--- <---Resv---
================RSVP===>
**************************************>
---Path---> --Path--->
(R2) (R2) \-------------Path---->
/ (R2)
<--Resv--- <---Resv---
<----Resv---
================RSVP===========================>
***********************************************>
|****| RSVP-capable |----| non-RSVP-capable |****| RSVP-capable
| S | Sender | R | Receiver | R | Receiver
|****| |----| |****|
***
*r* regular RSVP
*** router
(R1) = Path message contains a Session object whose destination is R1
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 6: Dynamic Discovery of Downstream RSVP Functionality
Le Faucheur, et al. Standards Track PAGE 25
RFC 5946 RSVP Receiver Proxy Extensions October 2010
If there is no RSVP-capable receiver (or other Receiver Proxy)
downstream of the Receiver Proxy, then the Path messages sent by the
Receiver Proxy every RSVP refresh interval (e.g., 30 seconds by
default) will never be responded to. However, these messages consume
a small amount of bandwidth, and in addition would install some RSVP
state on RSVP-capable midpoint nodes downstream of the first Receiver
Proxy. This is seen as a very minor sub-optimality; however, to
mitigate this, the Receiver Proxy MAY tear down any unanswered
downstream Path state after a predetermined time (that SHOULD be
greater or equal to the Path refresh interval), and MAY stop sending
Path messages for the flow (or MAY only send them at much lower
frequency).
This approach only requires support of the behavior described in the
previous paragraph and does not require any new RSVP extensions.
4.2. Receiver Proxy Control Policy Element
[RFC 2750] defines extensions for supporting generic policy-based
admission control in RSVP. These extensions include the standard
format of POLICY_DATA objects and a description of RSVP handling of
policy events.
The POLICY_DATA object contains one or more policy elements, each
representing a different (and perhaps orthogonal) policy. As an
example, [RFC 3181] specifies the preemption priority policy element.
This document defines a new policy element called the Receiver Proxy
Control policy element. This document only defines the use of this
policy element in Path messages and for unicast reservations. Other
usage is outside the scope of this document.
The format of the Receiver Proxy Control policy element is as shown
in Figure 7:
0 0 0 1 1 2 2 3
0 . . . 7 8 . . . 5 6 . . . 3 4 . . . 1
+-------------+-------------+-------------+-------------+
| Length | P-Type=REC_PROXY_CONTROL |
+-------------+-------------+-------------+-------------+
| Reserved |Control-Value|
+---------------------------+---------------------------+
Figure 7: Receiver Proxy Control Policy Element
Le Faucheur, et al. Standards Track PAGE 26
RFC 5946 RSVP Receiver Proxy Extensions October 2010
where:
o Length: 16 bits
* Always 8. The overall length of the policy element, in bytes.
o P-Type: 16 bits
* REC_PROXY_CONTROL = 0x07 (see the "IANA Considerations"
section).
o Reserved: 24 bits
* SHALL be set to zero on transmit and SHALL be ignored on
reception.
o Control-Value: 8 bits (unsigned)
* 0 (Reserved): An RSVP Receiver Proxy that understands this
policy element MUST ignore the policy element if its Control-
Value is set to that value.
* 1 (Receiver-Proxy-Needed): An RSVP Receiver Proxy that
understands this policy element MUST attempt to insert itself
as a Receiver Proxy for that flow if the corresponding Path
message contains this Control-Value. If the Receiver Proxy
also supports dynamic discovery of downstream RSVP
functionality as specified in Section 4.1, it MUST still send
the Path message downstream and attempt to extend the
reservation downstream so that the reservation can be extended
to the last Receiver Proxy). An RSVP sender MAY insert the
Receiver Proxy Control policy element with this Control-Value
when it knows (say, by other means, such as application-level
signaling) that the receiver is not RSVP-capable.
* 2 (Receiver-Proxy-Not-Needed): An RSVP Receiver Proxy that
understands this policy element MUST NOT attempt to insert
itself as a Receiver Proxy for that flow if the corresponding
Path message contains this Control-Value. An RSVP sender MAY
insert the Receiver Proxy Control policy element with this
Control-Value when it knows (say, by other means, such as
application-level signaling) that the receiver is RSVP-capable.
Figure 8 illustrates the method based on the Receiver Proxy Control
policy element that allows a sender to control whether or not an RSVP
router supporting the Path-Triggered Receiver Proxy function is to
behave as a Receiver Proxy for a given flow.
Le Faucheur, et al. Standards Track PAGE 27
RFC 5946 RSVP Receiver Proxy Extensions October 2010
|****| *** |**********| |----|
| S |---------*r*---------| RSVP |---| R1 |
|****| *** | Receiver | |----|
| Proxy |
| |
| | |****|
| |------------| R2 |
|**********| |****|
---Path---> --Path--->
(R1/N) (R1/N)
<--Resv--- <---Resv---
================RSVP===>
**************************************>
---Path---> --Path---> ----Path---->
(R2/NN) (R2/NN) (R2/NN)
<--Resv--- <---Resv--- <----Resv----
================RSVP===========================>
***********************************************>
|****| RSVP-capable |----| non-RSVP-capable |****| RSVP-capable
| S | Sender | R | Receiver | R | Receiver
|****| |----| |****|
***
*r* regular RSVP
*** router
(R1) = Path message contains a Session object whose destination is R1
(N) = Path message contains a Receiver Proxy Control policy element
whose Control-Value is set to Receiver-Proxy-Needed
(NN) = Path message contains a Receiver Proxy Control policy element
whose Control-Value is set to Receiver-Proxy-Not-Needed
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 8: Receiver Proxy Control by Sender
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4.2.1. Default Handling
As specified in Section 4.2 of [RFC 2750], Policy-Ignorant Nodes
(PINs) implement a default handling of POLICY_DATA objects ensuring
that those objects can traverse PINs in transit from one Policy
Enforcement Point (PEP) to another. This applies to the situations
in which POLICY_DATA objects contain the Receiver Proxy Control
policy element specified in this document, so that those objects can
traverse PINs.
Section 4.2 of [RFC 2750] also defines a similar default behavior for
policy-capable nodes that do not recognize a particular policy
element. This applies to the Receiver Proxy Control policy element
specified in this document, so that messages carrying the element can
traverse policy-capable nodes that do not support the extensions
described in this document.
5. Security Considerations
As this document defines extensions to RSVP, the security
considerations of RSVP apply, which are discussed in [RFC 2205],
[RFC 4230], and [SEC-GRP-KEY]. Approaches for addressing those
concerns are discussed further below.
The RSVP authentication mechanisms defined in [RFC 2747] and [RFC 3097]
protect RSVP message integrity hop-by-hop and provide node
authentication as well as replay protection, thereby protecting
against corruption and spoofing of RSVP messages. These hop-by-hop
integrity mechanisms can be used to protect RSVP reservations
established using an RSVP Receiver Proxy in accordance with this
document. [SEC-GRP-KEY] discusses key types and key provisioning
methods as well as their respective applicability to RSVP
authentication. RSVP authentication (defined in [RFC 2747] and
[RFC 3097]) SHOULD be supported by an implementation of this document.
[SEC-GRP-KEY] also discusses applicability of IPsec mechanisms
([RFC 4302], [RFC 4303]) and associated key provisioning methods for
security protection of RSVP. This discussion applies to the
protection of RSVP in the presence of Path-Triggered RSVP Receiver
Proxies as defined in this document.
A subset of RSVP messages are signaled with the IP router alert
option ([RFC 2113], [RFC 2711]). Based on the current security
concerns associated with the use of the IP router alert option, the
applicability of RSVP (and therefore of the RSVP Proxy approaches
discussed in this document) is limited to controlled environments
Le Faucheur, et al. Standards Track PAGE 29
RFC 5946 RSVP Receiver Proxy Extensions October 2010
(i.e., where the security risks associated with the use of the IP
router alert option are understood and protected against). The
security aspects and common practices around the use of the current
IP router alert option, and consequences of using the IP router alert
option by applications such as RSVP, are discussed in detail in
[RTR-ALERT].
When an RSVP Receiver Proxy is used, the RSVP reservation is no
longer controlled by the receiver, but rather is controlled by the
Receiver Proxy (using hints received from the sender in the Path
message) on behalf of the sender. Thus, the Receiver Proxy ought to
be trusted by the end-systems to control the RSVP reservation
appropriately. However, basic RSVP operation already assumes a trust
model where end-systems trust RSVP nodes to appropriately perform
RSVP reservations. So the use of an RSVP Receiver Proxy is not seen
as introducing any significant additional security threat or as
modifying the RSVP trust model.
In fact, there are situations in which the use of an RSVP Receiver
Proxy reduces the security risks. One example is where a network
operator relies on RSVP to perform resource reservation and admission
control within a network and where RSVP senders and RSVP routers are
located in the operator's premises, while the many RSVP receivers are
located in the operator's customers' premises. Such an environment
is further illustrated in Appendix A.1, "RSVP-Based VoD Admission
Control in Broadband Aggregation Networks", of [RFC 5945]. From the
operator's perspective, the RSVP routers and RSVP senders are in
physically secured locations and therefore exposed to a lower risk of
being tampered with, while the receivers are in locations that are
physically unsecured and therefore subject to a higher risk of being
tampered with. The use of an RSVP Receiver Proxy function
effectively increases the security of the operator's reservation and
admission control solution by completely excluding receivers from its
operation. Filters can be placed at the edge of the operator
network, discarding any RSVP message received from end-users. This
provides a very simple and effective protection of the RSVP
reservation and admission control solution operating inside the
operator's network.
5.1. Security Considerations for the Sender Notification via Notify
Message
This document defines, in Section 3.2, an optional method relying on
the use of the Notify message specified in [RFC 3473]. The Notify
message can be sent in a non-hop-by-hop fashion that precludes the
use of the RSVP hop-by-hop integrity and authentication model. The
approaches and considerations for addressing this issue presented in
the Security Considerations section of [RFC 3473] apply. In
Le Faucheur, et al. Standards Track PAGE 30
RFC 5946 RSVP Receiver Proxy Extensions October 2010
particular, where the Notify messages are transmitted non-hop-by-hop
and the same level of security provided by [RFC 2747] is desired,
IPsec-based integrity and authentication can be used ([RFC 4302] or
[RFC 4303]). Alternatively, the sending of non-hop-by-hop Notify
messages can be disabled. Finally, [SEC-GRP-KEY] discusses the
applicability of group keying for non-hop-by-hop Notify messages.
5.2. Security Considerations for the Receiver Proxy Control Policy
Element
This document also defines, in Section 4.2, the optional Receiver
Proxy Control policy element. Policy elements are signaled by RSVP
through encapsulation in a Policy Data object as defined in
[RFC 2750]. Therefore, like any other policy elements, the integrity
of the Receiver Proxy Control policy element can be protected as
discussed in Section 6 of [RFC 2750] by two optional security
mechanisms.
The first mechanism relies on the RSVP authentication discussed above
that provides a chain of trust when all RSVP nodes are policy
capable. With this mechanism, the INTEGRITY object is carried inside
RSVP messages.
The second mechanism relies on the INTEGRITY object within the
POLICY_DATA object to guarantee integrity between RSVP Policy
Enforcement Points (PEPs) that are not RSVP neighbors. This is
useful only when some RSVP nodes are Policy-Ignorant Nodes (PINs).
The INTEGRITY object within the POLICY_DATA object MAY be supported
by an implementation of this document.
Details for the computation of the content of the INTEGRITY object
can be found in Appendix B of [RFC 2750]. This states that the Policy
Decision Point (PDP), at its discretion, and based on destination
PEP/PDP or other criteria, selects an Authentication Key and the hash
algorithm to be used. Keys to be used between PDPs can be
distributed manually or via a standard key management protocol for
secure key distribution.
Note that where non-RSVP hops may exist in between RSVP hops, as well
as where RSVP-capable Policy-Ignorant Nodes (PINs) may exist in
between PEPs, it may be difficult for the PDP to determine what the
destination PDP is for a POLICY_DATA object contained in some RSVP
messages (such as a Path message). This is because in those cases,
the next PEP is not known at the time of forwarding the message. In
this situation, a key shared across multiple PDPs may be used. This
is conceptually similar to the use of a key shared across multiple
RSVP neighbors, as discussed in [SEC-GRP-KEY]. We also observe that
this issue may not exist in some deployment scenarios where a single
Le Faucheur, et al. Standards Track PAGE 31
RFC 5946 RSVP Receiver Proxy Extensions October 2010
PDP (or a low number of PDPs) is used to control all the PEPs of a
region (such as an administrative domain). In such scenarios, it may
be easy for a PDP to determine what the next-hop PDP is, even when
the next-hop PEP is not known, simply by determining what the next
region is that will be traversed (say, based on the destination
address).
6. IANA Considerations
6.1. RSVP Error Codes
Since, as discussed in Section 3.1.2, this document allows two error
codes to be used in PathErr messages while [RFC 2205] only specified
their use in ResvErr messages, IANA has updated the existing entries
for these two error codes under the "Error Codes and Globally-Defined
Error Value Sub-Codes" registry. Each entry refers to this document,
in addition to referring to [RFC 2205]. Specifically, the entry for
Error Code 1 and Error Code 2 read:
1 Admission Control Failure [RFC 2205] [RFC 5946]
2 Policy Control Failure [RFC 2205] [RFC 5946]
IANA has also allocated a new RSVP Error Code "36;: Unrecoverable
Receiver Proxy Error", as discussed in Section 3.1.2. This error
code has been allocated under the "Error Codes and Globally-Defined
Error Value Sub-Codes" registry. The entry for this error code
reads:
36 Unrecoverable Receiver Proxy Error [RFC 5946]
The sixteen bits of the Error Value field are defined in [RFC 5946]
6.2. Policy Element
This document defines, in Section 4.2, a new policy element called
the Receiver Proxy Control policy element. As specified in
[RFC 2750], standard RSVP policy elements (P-Type values) are to be
assigned by IANA as per "IETF Consensus" policy following the
policies outlined in [RFC 2434] (this policy is now called "IETF
Review" as per [RFC 5226]).
Thus, IANA has allocated one P-Type to the Receiver Proxy Control
policy element from the standard RSVP policy element range.
Le Faucheur, et al. Standards Track PAGE 32
RFC 5946 RSVP Receiver Proxy Extensions October 2010
In Section 4.2, this document defines a Control-Value field inside
the Receiver Proxy Control policy element. IANA has created the
"Receiver Proxy Control Policy Element (P-Type 0x07) Control-Value
field" registry and allocated the following values:
o 0 : Reserved
o 1 : Receiver-Proxy-Needed
o 2 : Receiver-Proxy-Not-Needed
Following the policies outlined in [RFC 5226], numbers in the range
3-127 are allocated according to the "IETF Review" policy, numbers in
the range 128-240 are assigned on a "First Come First Served" basis,
and numbers in the range 241-255 are reserved for "Private Use".
7. Acknowledgments
This document benefited from discussions with Carol Iturralde and
Anca Zamfir. Lou Berger, Adrian Farrel, and John Drake provided
review and guidance, in particular on the usage of the
Path_State_Removed flag and of the Notify message, both borrowed from
[RFC 3473]. We also thank Stephen Kent, Ken Carlberg, and Tim Polk
for their valuable input and proposed enhancements. Finally, we
thank Cullen Jennings, Magnus Westerlund, and Robert Sparks for
stimulating the work on extensions maximizing the reservation span
and facilitating migration from the Proxy model to the end-to-end
RSVP model.
8. References
8.1. Normative References
[RFC 2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
1 Functional Specification", RFC 2205, September 1997.
[RFC 2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 2434, October 1998.
Le Faucheur, et al. Standards Track PAGE 33
RFC 5946 RSVP Receiver Proxy Extensions October 2010
[RFC 2711] Partridge, C. and A. Jackson, "IPv6 Router Alert
Option", RFC 2711, October 1999.
[RFC 2747] Baker, F., Lindell, B., and M. Talwar, "RSVP
Cryptographic Authentication", RFC 2747, January 2000.
[RFC 2750] Herzog, S., "RSVP Extensions for Policy Control",
RFC 2750, January 2000.
[RFC 3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value",
RFC 3097, April 2001.
[RFC 3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
V., and G. Swallow, "RSVP-TE: Extensions to RSVP for
LSP Tunnels", RFC 3209, December 2001.
[RFC 3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[RFC 4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC 4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
8.2. Informative References
[RFC 3181] Herzog, S., "Signaled Preemption Priority Policy
Element", RFC 3181, October 2001.
[RFC 4230] Tschofenig, H. and R. Graveman, "RSVP Security
Properties", RFC 4230, December 2005.
[RFC 5945] Le Faucheur, F., Manner, J., Wing, D., and A. Guillou,
"Resource Reservation Protocol (RSVP) Proxy
Approaches", RFC 5945, October 2010.
[RTR-ALERT] Le Faucheur, F., "IP Router Alert Considerations and
Usage", Work in Progress, October 2009.
Le Faucheur, et al. Standards Track PAGE 34
RFC 5946 RSVP Receiver Proxy Extensions October 2010
[SEC-GRP-KEY] Behringer, M. and F. Le Faucheur, "Applicability of
Keying Methods for RSVP Security", Work in Progress,
June 2010.
Authors' Addresses
Francois Le Faucheur
Cisco Systems
Greenside, 400 Avenue de Roumanille
Sophia Antipolis 06410
France
Phone: +33 4 97 23 26 19
EMail: flefauch@cisco.com
Jukka Manner
Aalto University
Department of Communications and Networking (Comnet)
P.O. Box 13000
FIN-00076 Aalto
Finland
Phone: +358 9 470 22481
EMail: jukka.manner@tkk.fi
URI: http://www.netlab.tkk.fi/~jmanner/
Ashok Narayanan
Cisco Systems
300 Beaver Brook Road
Boxborough, MA 01719
United States
EMail: ashokn@cisco.com
Allan Guillou
SFR
40-42 Quai du Point du Jour
Boulogne-Billancourt 92659
France
EMail: allan.guillou@sfr.com
Hemant Malik
Bharti Airtel, Ltd.
4th Floor, Plot No. 16
Udyog Vihar, Phase IV
Gurgaon, 122015
India
EMail: Hemant.Malik@airtel.in
Le Faucheur, et al. Standards Track PAGE 35
Resource Reservation Protocol (RSVP) Extensions for Path-Triggered RSVP Receiver Proxy
RFC TOTAL SIZE: 81414 bytes
PUBLICATION DATE: Monday, October 11th, 2010
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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