TSVWG F. Le Faucheur
Internet-Draft Cisco
Intended status: Standards Track J. Manner
Expires: November 5, 2009 University of Helsinki
A. Narayanan
Cisco
A. Guillou
Neuf
H. Malik
Bharti
May 4, 2009
RSVP Extensions for Path-Triggered RSVP Receiver Proxy
draft-ietf-tsvwg-rsvp-proxy-proto-09.txt
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Abstract
RSVP signaling can be used to make end-to-end resource reservations
in an IP network in order to guarantee the 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 presenting 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Conventions Used in This Document . . . . . . . . . . . . 7
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. RSVP Extensions for Sender Notification . . . . . . . . . . . 9
3.1. Sender Notification via PathErr Message . . . . . . . . . 12
3.1.1. Composition of SESSION and Sender Descriptor . . . . . 15
3.1.2. Composition of ERROR_SPEC . . . . . . . . . . . . . . 15
3.1.3. Use of Path_State_Removed Flag . . . . . . . . . . . . 16
3.1.4. Use of PathErr by Regular Receivers . . . . . . . . . 17
3.2. Sender Notification via Notify Message . . . . . . . . . . 18
4. Security Considerations . . . . . . . . . . . . . . . . . . . 26
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. Normative References . . . . . . . . . . . . . . . . . . . 31
7.2. Informative References . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
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1. Introduction
Guaranteed 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 RSVP
specified in [RFC2205]. 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
[I-D.ietf-tsvwg-rsvp-proxy-approaches]. 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 changes somewhat 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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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 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. This document specifies extension to RSVP
procedures allowing such notifications also to be conveyed towards
the sender. This facilitates synchronization by the sender (or RSVP
Sender Proxy) between the RSVP reservation and the application
requirements and 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 the present 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 establishment (respectively removal) of the
reservation towards the receiver by sending Path (respectively
PathTear) messages. 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 signalling 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
message and stopping transmission whenever it gets a notification for
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reservation reject for one or more RSVP Receiver Proxy. It is also
possible to support a mode of operation whereby receivers join
independently of whether they can benefit from a reservation (to
their respective RSVP Receiver Proxy) or not, 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 operation assuming a regular RSVP
sender; however, such operation is equally applicable where an RSVP
Sender Proxy is used to initiated RSVP signaling on behalf of a non-
RSVP-capable sender.
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 [RFC2119].
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2. Terminology
The following terminology is borrowed from
[I-D.ietf-tsvwg-rsvp-proxy-approaches] and is used extensively in the
present document:
o RSVP-capable (or RSVP-aware): supporting the RSVP protocol as per
[RFC2205]
o RSVP Receiver Proxy: an RSVP-capable router performing, on behalf
of a receiver, the RSVP operations which would normally be
performed by an RSVP-capable receiver if end-to-end RSVP signaling
was 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 was 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 which is not behaving
as a RSVP Receiver Proxy nor as a RSVP Sender Proxy.
Note that the roles of RSVP Receiver Proxy, RSVP Sender Proxy,
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 the present 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 [RFC2205].
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
[RFC2205].
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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 [I-D.ietf-tsvwg-rsvp-proxy-approaches], 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 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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|----| *** *** *** |----------| |----|
| 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 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 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.
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|----| *** *** *** |----------| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|----| *** *** *** | Receiver | |----|
| Proxy |
|----------|
--Path---> --Path---> --Path---> --Path--->
<---Resv-- <---Resv--
-ResvErr-> -ResvErr->
===================RSVP===================>
************************************************************>
|----| |----| ***
| 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 in ensuring that the sender gets a prompt, explicit
notification in case of reservation failure. This includes faster
end-user notification at application layer (e.g., busy signal),
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.
In a given network environment, a network administrator may elect to
use the method defined in Section 3.1, or the method defined in
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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 [RFC3209] where it has been
introduced in order to achieve a similar requirement, which is to
allow an MPLS TE Label Switch 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 PathErr
Message, is illustrated in Figure 3.
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|----| *** *** *** |----------| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|----| *** *** *** | Receiver | |----|
| Proxy |
|----------|
--Path---> --Path---> --Path---> --Path--->
<---Resv-- <---Resv--
-ResvErr-> -ResvErr->
<-PathErr- <-PathErr- <-PathErr- <-PathErr-
===================RSVP===================>
************************************************************>
|----| |----| ***
| 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 which would not ordinarily cause generation of a ResvErr
message, such as described in Appendix B of [RFC2205].
The PathErr generated by the Receiver Proxy corresponds to the
sender(s) that triggered generation of Resv messages that failed.
For Fixed-Filter (FF) style reservations, the Receiver Proxy MUST
send a PathErr towards the (single) sender matching the failed
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reservation. For Shared-Explicit (SE) style reservations, the
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
[RFC2205] for generating flow descriptors in ResvErr messages, also
apply when generating sender descriptors in PathErr messages.
For Wildcard-Filter (WF) style 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 PathErr message is
somewhat over-conservative (i.e., in some cases rejecting
reservations from some senders when those could have actually been
established) when used in combination with Wildcard-Filter style (and
when there is more than one sender).
The sender notification via 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 those errors should explicitly be communicated back to the
sender. An examples of this is "Class 1: Admission Control
Failure", because the sender could potentially resend a Path 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 "Class 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 [RFC2205]. The
SESSION, ERROR_SPEC and sender descriptor are composed by the
Receiver Proxy as specified in the following subsections. The
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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 Fixed-Filter (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 Shared-Explicit (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 [RFC2205].
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 Wildcard-Filter 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 any 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
other than the ones listed in 1 above, it composes a new
ERROR_SPEC with error code "<TBD-See IANA Considerations
section>: Unrecoverable Receiver Proxy Error". 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 any error code except than those listed in 1
above, or if the Receiver Proxy generates a PathErr for a local
error which ordinarily would not cause generation of a ResvErr.
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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 which
could not process the Resv. Nevertheless, the procedures above
MUST be followed. For the error code "<TBD-See IANA
Considerations section>: 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 of 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
[RFC3473] 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 [RFC3473].
By default, the RSVP Receiver Proxy MUST NOT include the
Path_State_Removed flag in the ERROR_SPEC of the PathErr message.
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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 router 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 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 to modify the behavior
of regular receivers as currently specified in [RFC2205]. The
rationale for this includes the following:
o When the receiver is RSVP capable, the current receiver-driven
model of [RFC2205] is fully applicable because the receiver can
synchronise RSVP reservation state and application state (since it
participates in both). The sender(s) needs not be aware of the
RSVP reservation state. Thus, we can retain the benefits of
receiver-driven operations which were explicitly sought by
[RFC2205]. Quoting from it: " In order to efficiently accommodate
large groups, dynamic group membership, and heterogeneous receiver
requirements, RSVP makes receivers responsible for requesting a
specific QoS". But even for the simplest single_sender/
single_receiver reservations, the current receiver-driven model
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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 case of
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 case of regular
receiver.
o There is a lot of existing code and deployed systems successfully
working under the current [RFC2205] model in the absence of proxy
today. The current behavior should not be changed for those
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 allow the failure notification to be sent directly upstream to the
sender by the router where the failure occurs (as opposed to first
travelling downstream towards the Receiver Proxy and then
travelling upstream from the Receiver Proxy to the sender, as
effectively happens with the method defined in Section 3.1)
o allow the failure notification to travel without hop-by-hop RSVP
processing
o ensure 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 ensure 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 [RFC3473]
o a requirement for senders to process Notify messages traveling
upstream but conveying a downstream notification.
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[RFC3473] 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 [RFC2205] (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 [RFC3473].
In order to achieve sender notification of reservation failure in the
context of the present 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".
* or an address of the Receiver Proxy. We refer to this approach
as the "Indirect Notify".
o Upon receiving a downstream error notification (whether in the
form of a Notify or a 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
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
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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
address (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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|----| *** *** *** |----------| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|----| *** *** *** | Receiver | |----|
| Proxy |
|----------|
--Path*--> --Path*--> --Path*--> --Path*-->
<--Resv*-- <--Resv*--
<------NotifyD--------
-ResvErr-> -ResvErr->
<------------------NotifyU------------------
<-PathErr- <-PathErr- <-PathErr- <-PathErr-
===================RSVP===================>
************************************************************>
|----| |----| ***
| 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
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Notify, is illustrated in Figure 5.
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|----| *** *** *** |----------| |----|
| S |--------*r*--------*r*--------*r*--------| RSVP |------| R |
|----| *** *** *** | Receiver | |----|
| Proxy |
|----------|
--Path*--> --Path*--> --Path*--> --Path*-->
<--Resv*-- <--Resv*--
-------NotifyD------->
<------------------NotifyU------------------
-ResvErr-> -ResvErr->
<-PathErr- <-PathErr- <-PathErr- <-PathErr-
===================RSVP===================>
************************************************************>
|----| |----| ***
| 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
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example, admission control failure), the Receiver Proxy MUST generate
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 described in Appendix B of
[RFC2205].
When the method of sender notification via 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
Notify message and thus not issue sender notification via 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
issues 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,
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does not prevent a sender that does not support this method, to rely
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 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 (respectively, SE) a Notify MUST
be sent to the sender (respectively, the set of affected senders).
With WF, the RSVP Receiver Proxy SHOULD send a Notify to each sender,
again resulting in a somewhat over-conservative behavior in the
presence of multiple senders.
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4. Security Considerations
To ensure the integrity and authenticity of the associated
reservation and admission control mechanisms, the RSVP Authentication
mechanisms defined in [RFC2747] and [RFC3097] can be used. Those
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 the
present document.
[RFC2747] discusses several approaches to key distribution. First,
the RSVP Authentication shared keys can be distributed manually.
This is the base option and its support is mandated for every
implementation. However, in some environments, this approach may
become a burden if keys change frequently over time. Alternatively,
a standard key management protocol for secure key distribution can be
used.
The use of RSVP Authentication in parts of the network where there
may be one or more IP hops in between two RSVP neighbors raises an
additional challenge. This is because, with some RSVP messages such
as a Path message, an RSVP router does not know the RSVP next hop for
that message at the time of forwarding it. In fact, part of the role
of a Path message is precisely to discover the RSVP next hop (and to
dynamically re-discover it when it changes, say because of a routing
change). Hence, the RSVP router may not know which security
association to use when forwarding such a message (see [RFC2747] for
definition of RSVP security association). In that situation, one
approach is to share the same RSVP Authentication key across all the
RSVP routers in a part of the network where there may be RSVP
neighbors with IP hops in between. For example, all the RSVP routers
of an administrative domain (including the receiver proxies) could
share the same RSVP Authentication key, while different per-neighbor
keys could be used between any RSVP router pair straddling the
boundary between two administrative domains that have agreed to use
RSVP signaling.
When the same RSVP Authentication key is to be shared among multiple
RSVP neighbors, manual key distribution may be used.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] also discusses
applicability of dynamic group key distribution method for dynamic
update of such shared keys among RSVP routers.
The RSVP Authentication mechanisms do not provide confidentiality.
If confidentiality is required, IPsec ESP ([RFC4303]) may be used,
although it imposes the burden of key distribution. It also faces
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the additional issue discussed for key management above in the case
where there can be IP hops in between RSVP hops.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] discusses applicability of
various keying methods for applying IPsec encryption and
authentication to RSVP, including use of group keys and dynamic group
key distribution.
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 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 where the use of 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 premises while the many RSVP receivers are located in
the operator's customers premises. Such an environment is further
illustrated in "Annex A.1. RSVP-based VoD Admission Control in
Broadband Aggregation Networks" of
[I-D.ietf-tsvwg-rsvp-proxy-approaches]. 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.
This document defines in Section 3.2 an optional method relying on
the use of the Notify message specified in [RFC3473]. The Notify
message can be sent in a non-hop-by-hop fashion that precludes use of
RSVP hop-by-hop integrity and authentication model. The approaches
and considerations for addressing this issue presented in the
Security Considerations section of [RFC3473] apply. In particular,
where the Notify messages are transmitted non-hop-by-hop and the same
level of security provided by [RFC2747] is desired, IPsec-based
integrity and authentication can be used ([RFC4302] or [RFC4303]).
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Alternatively, the sending of non-hop-by-hop Notify messages can be
disabled. Finally, [I-D.ietf-tsvwg-rsvp-security-groupkeying]
discusses applicability of group keying for non-hop-by-hop Notify
messages.
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5. IANA Considerations
Since, as discussed in Section 3.1.2, this document allows two Error
Codes to be used in PathErr messages while [RFC2205] only specified
their use in ResvErr messages, this document requires that IANA
updates the existing entries for these two Error Codes under the
"Error Codes and Globally-Defined Error Value Sub-Codes" registry.
Each entry should refer to this document, in addition to referring to
[RFC2205]. Specifically, the entry for Error Code 1 and Error Code 2
should respectively read:
"
1 Admission Control Failure [RFC2205] [RFCXXX]
...
2 Policy Control Failure [RFC2205] [RFCXXX]
...
"
where [RFCXXX] refers to this document.
This document also requires that IANA allocates a new RSVP Error Code
"<TBD>: Unrecoverable Receiver Proxy Error", as discussed in
Section 3.1.2. This Error Code is to be allocated under the "Error
Codes and Globally-Defined Error Value Sub-Codes" registry. The
entry for this error code should read:
"
TBD Unrecoverable Receiver Proxy Error [RFCXXX]
The sixteen bits of the Error Value field are defined in [RFCXXX]
"
where [RFCXXX] refers to this document and TBD is the value to be
allocated by IANA.
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6. 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
[RFC3473]. We also thank Ken Carlberg for his valuable input.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, January 2000.
[RFC3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value", RFC 3097,
April 2001.
[RFC3209] 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.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
7.2. Informative References
[I-D.ietf-tsvwg-rsvp-proxy-approaches]
Faucheur, F., Manner, J., Wing, D., and A. Guillou, "RSVP
Proxy Approaches",
draft-ietf-tsvwg-rsvp-proxy-approaches-06 (work in
progress), October 2008.
[I-D.ietf-tsvwg-rsvp-security-groupkeying]
Behringer, M. and F. Faucheur, "Applicability of Keying
Methods for RSVP Security",
draft-ietf-tsvwg-rsvp-security-groupkeying-04 (work in
progress), March 2009.
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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
University of Helsinki
P.O. Box 68
University of Helsinki FIN-00014 University of Helsinki
Finland
Phone: +358 9 191 51298
Email: jmanner@cs.helsinki.fi
URI: http://www.cs.helsinki.fi/u/jmanner/
Ashok Narayanan
Cisco Systems
300 Beaver Brook Road
Boxborough, MAS 01719
United States
Email: ashokn@cisco.com
Allan Guillou
Neuf Cegetel
40-42 Quai du Point du Jour
Boulogne-Billancourt, 92659
France
Email: allan.guillou@sfr.com
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Hemant Malik
Bharti Airtel Ltd.
4th Floor, Tower A, Unitech Cyber Park
Gurgaon, Sector 39, 122001
India
Email: Hemant.Malik@airtel.in
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