Network Working Group B. Davie
Internet-Draft F. le Faucheur
Intended status: Standards Track A. Narayanan
Expires: October 27, 2010 Cisco Systems, Inc.
April 25, 2010
Support for RSVP in Layer 3 VPNs
draft-ietf-tsvwg-rsvp-l3vpn-06.txt
Abstract
RFC 4364 and RFC 4659 define an approach to building provider-
provisioned Layer 3 VPNs for IPv4 and IPv6. It may be desirable to
use RSVP to perform admission control on the links between Customer
Edge (CE) routers and Provider Edge (PE) routers. This document
specifies procedures by which RSVP messages travelling from CE to CE
across an L3VPN may be appropriately handled by PE routers so that
admission control can be performed on PE-CE links. Optionally,
admission control across the provider's backbone may also be
supported.
Requirements Language
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 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 27, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Model of Operation . . . . . . . . . . . . . . . . . . . . 7
3. Admission Control on PE-CE Links . . . . . . . . . . . . . . . 9
3.1. New Objects of Type VPN-IPv4 . . . . . . . . . . . . . . . 9
3.2. Path Message Processing at Ingress PE . . . . . . . . . . 11
3.3. Path Message Processing at Egress PE . . . . . . . . . . . 12
3.4. Resv Processing at Egress PE . . . . . . . . . . . . . . . 12
3.5. Resv Processing at Ingress PE . . . . . . . . . . . . . . 13
3.6. Other RSVP Messages . . . . . . . . . . . . . . . . . . . 13
4. Admission Control in Provider's Backbone . . . . . . . . . . . 14
5. Inter-AS operation . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Inter-AS Option A . . . . . . . . . . . . . . . . . . . . 15
5.2. Inter-AS Option B . . . . . . . . . . . . . . . . . . . . 15
5.2.1. Admission control on ASBR . . . . . . . . . . . . . . 15
5.2.2. No admission control on ASBR . . . . . . . . . . . . . 16
5.3. Inter-AS Option C . . . . . . . . . . . . . . . . . . . . 17
6. Operation with RSVP disabled . . . . . . . . . . . . . . . . . 17
7. Other RSVP procedures . . . . . . . . . . . . . . . . . . . . 17
7.1. Refresh overhead reduction . . . . . . . . . . . . . . . . 18
7.2. Cryptographic Authentication . . . . . . . . . . . . . . . 18
7.3. RSVP Aggregation . . . . . . . . . . . . . . . . . . . . . 18
7.4. Support for CE-CE RSVP-TE . . . . . . . . . . . . . . . . 19
8. Object Definitions . . . . . . . . . . . . . . . . . . . . . . 19
8.1. VPN-IPv4 and VPN-IPv6 SESSION objects . . . . . . . . . . 19
8.2. VPN-IPv4 and VPN-IPv6 SENDER_TEMPLATE objects . . . . . . 21
8.3. VPN-IPv4 and VPN-IPv6 FILTER_SPEC objects . . . . . . . . 22
8.4. VPN-IPv4 and VPN-IPv6 RSVP_HOP objects . . . . . . . . . . 22
8.5. Aggregated VPN-IPv4 and VPN-IPv6 SESSION objects . . . . . 24
8.6. AGGREGATE-VPN-IPv4 and AGGREGATE-VPN-IPv6
SENDER_TEMPLATE objects . . . . . . . . . . . . . . . . . 26
8.7. AGGREGATE-VPN-IPv4 and AGGREGATE-VPN-IPv6 FILTER_SPEC
objects . . . . . . . . . . . . . . . . . . . . . . . . . 27
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
10. Security Considerations . . . . . . . . . . . . . . . . . . . 31
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
Appendix A. Alternatives Considered . . . . . . . . . . . . . . 34
Appendix A.1. GMPLS UNI approach . . . . . . . . . . . . . . . . . 34
Appendix A.2. VRF label approach . . . . . . . . . . . . . . . . . 34
Appendix A.3. VRF label plus VRF address approach . . . . . . . . 35
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
12.1. Normative References . . . . . . . . . . . . . . . . . . . 35
12.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
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1. Introduction
[RFC4364] and [RFC4659] define a Layer 3 VPN service known as BGP/
MPLS VPNs for IPv4 and for IPv6 respectively. [RFC2205] defines the
Resource Reservation Protocol (RSVP) which may be used to perform
admission control as part of the Integrated Services (Int-Serv)
architecture [RFC1633][RFC2210].
Customers of a layer 3 VPN service may run RSVP for the purposes of
admission control (and associated resource reservation) in their own
networks. Since the links between Provider Edge (PE) and Customer
Edge (CE) routers in a layer 3 VPN may often be resource constrained,
it may be desirable to be able to perform admission control over
those links. In order to perform admission control using RSVP in
such an environment, it is necessary that RSVP control messages, such
as Path messages and Resv messages, are appropriately handled by the
PE routers. This presents a number of challenges in the context of
BGP/MPLS VPNs:
o RSVP Path message processing depends on routers recognizing the
router alert option ([RFC2113], [RFC2711]) in the IP header.
However, packets traversing the backbone of a BGP/MPLS VPN are
MPLS encapsulated and thus the router alert option may not be
normally visible to the egress PE, due to implementation or policy
considerations.
o BGP/MPLS VPNs support non-unique addressing of customer networks.
Thus a PE at the ingress or egress of the provider backbone may be
called upon to process Path messages from different customer VPNs
with non-unique destination addresses within the RSVP message.
Current mechanisms for identifying customer context from data
packets are incompatible with RSVP message processing rules.
o A PE at the ingress of the provider's backbone may receive Resv
messages corresponding to different customer VPNs from other PEs,
and needs to be able to associate those Resv messages with the
appropriate customer VPNs.
This document describes a set of procedures to overcome these
challenges and thus to enable admission control using RSVP over the
PE-CE links. We note that similar techniques may be applicable to
other protocols used for admission control such as the combination of
the NSIS Signaling Layer Protocol (NSLP) for QoS Signaling
([I-D.ietf-nsis-qos-nslp]) and General Internet Signaling Transport
(GIST) protocol ([I-D.ietf-nsis-ntlp]).
Additionally, it may be desirable to perform admission control over
the provider's backbone on behalf of one or more L3VPN customers.
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Core (P) routers in a BGP/MPLS VPN do not have forwarding entries for
customer routes, and thus cannot natively process RSVP messages for
customer flows. Also the core is a shared resource that carries
traffic for many customers, so issues of resource allocation among
customers and trust (or lack thereof) also ought to be addressed.
This document specifies procedures for supporting such a scenario.
This document deals with establishing reservations for unicast flows
only. Because the support of multicast traffic in BGP/MPLS VPNs is
still evolving, and raises additional challenges for admission
control, we leave the support of multicast flows for further study at
this point.
1.1. Terminology
This document draws freely on the terminology defined in [RFC2205]
and [RFC4364]. For convenience, we provide a few brief definitions
here:
o CE (Customer Edge) Router: Router at the edge of a customer site
that attaches to the network of the VPN provider.
o PE (Provider Edge) Router: Router at the edge of the service
provider's network that attaches to one or more customer sites.
o VPN Label: An MPLS label associated with a route to a customer
prefix in a VPN (also called a VPN route label).
o VRF: VPN Routing and Forwarding Table. A PE typically has
multiple VRFs, enabling it to be connected to CEs that are in
different VPNs.
2. Problem Statement
The problem space of this document is the support of admission
control between customer sites when the customer subscribes to a BGP/
MPLS VPN. We subdivide the problem into (a) the problem of admission
control on the PE-CE links (in both directions), and (b) the problem
of admission control across the provider's backbone.
RSVP Path messages are normally addressed to the destination of a
session, and contain the Router Alert Option (RAO) within the IP
header. Routers along the path to the destination that are
configured to process RSVP messages need to detect the presence of
the RAO to allow them to intercept Path messages. However, the
egress PEs of a network supporting BGP/MPLS VPNs receive packets
destined for customer sites as MPLS-encapsulated packets, and
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possibly forwards those based only on examination of the MPLS label.
Hence, a Path message would be forwarded without examination of the
IP options and would therefore not receive appropriate processing at
the PE. Another potential issue is doing CAC at an ASBR. Even an
implementation that examines the IP header when removing the VPN
label (e.g. PE-CE link) would not be able to do CAC at an Option-B
ASBR; that requires examining the (interior) IP header while doing a
label swap, which is a much less desirable feature. In general,
there are significant issues with requiring support for IP Router-
Alert outside of a controller, "walled-garden" network, as described
in [I-D.ietf-intarea-router-alert-considerations]. The issues with
requiring interior MPLS routers to process IP Router-Alert marked
packets are also described in [I-D.ietf-mpls-ip-options]. For these
reasons, it is highly desirable to remove the dependency on router
alert option across administrative domains (such as from a customer
network to an egress PE, or such as across ASBRs in inter- provider
MPLS VPN scenarios). The approach for RSVP packet handling described
in this document has the advantage of being independent of any data-
plane requirements such as IP Router-Alert support within the VPN.
The only requirement for processing IP Router-Alert packets is for
RSVP packets received from the CE, which do not carry any MPLS
encapsulation.
For the PE-CE link subproblem, the most basic challenge is that RSVP
control messages contain IP addresses that are drawn from the
customer's address space, and PEs need to deal with traffic from many
customers who may have non-unique (or overlapping) address spaces.
Thus, it is essential that a PE be able in all cases to identify the
correct VPN context in which to process an RSVP control message. The
current mechanism for identifying the customer context is the VPN
Label, which is carried in a MPLS header outside of the RSVP message.
This is divergent from the general RSVP model of session
identification ([RFC2205], [RFC2209]), which relies solely on RSVP
objects to identify sessions. Further, it is incompatible with
protocols like COPS/RSVP ([RFC2748],[RFC2748]), which replace the IP
encapsulation of the RSVP message and send only RSVP objects to a
COPS server. We believe it is important to retain the model of
completely identifying an RSVP session from the contents of RSVP
objects. Much of this document deals with this issue.
For the case of making reservations across the provider backbone, we
observe that BGP/MPLS VPNs do not create any per-customer forwarding
state in the P (provider core) routers. Thus, in order to make
reservations on behalf of customer-specified flows, it is clearly
necessary to make some sort of aggregated reservation from PE-PE and
then map individual, customer-specific reservations onto an aggregate
reservation. That is similar to the problem tackled in [RFC3175] and
[RFC4804], with the additional complications of handling customer-
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specific addressing associated with BGP/MPLS VPNs.
Consider the case where an MPLS VPN customer uses RSVP signaling
across his sites for resource reservation and admission control.
Let's further assume that, initially, RSVP is not processed through
the MPLS VPN cloud (i.e RSVP messages from the sender to the receiver
travel transparently from CE to CE). In that case, RSVP allows
establishment of resource reservations and admission control on a
subset of the flow path (from sender to ingress CE; and from the RSVP
router downstream of the egress CE to the receiver). If admission
control is then activated on any of the CE-PE link, provider's
backbone or PE-CE link (as allowed by the present document), the
customer will benefit from an extended coverage of admission control
and resource reservation: the resource reservation will now span over
a bigger subset of (and possibly the whole) flow path, which in turn
will increase the quality of service granted to the corresponding
flow. Specific flows whose reservation is successful through
admission control on the newly enabled segments will indeed benefit
from this quality of service enhancement. However, it must be noted
that, in case there is not enough resources on one (or more) of the
newly enabled segments (e.g. Say admission control is enabled on a
given PE-->CE link and there is not enough capacity on that link to
admit all reservations for all the flows traversing that link) then
some flows will not be able to maintain, or establish, their
reservation. While this may appear undesirable for these flows, we
observe that this only occurs if there is indeed a lack of capacity
on a segment, and that in the absence of admission control all flows
would be established but would all suffer from the resulting
congestion on the bottleneck segment. We also observe that, in case
of such lack of capacity, admission control allows enforcement of
controlled and flexible policies (so that, for example, more
important flows can be granted higher priority at reserving
resources). We note also that flows are given a chance to establish
smaller reservations so that the aggregate load can adapt dynamically
to the bottleneck capacity.
2.1. Model of Operation
Figure 1 illustrates the basic model of operation with which this
document is concerned.
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--------------------------
/ Provider \
|----| | Backbone | |----|
Sender->| CE1| |-----| |-----| |CE2 |->Receiver
| |--| | |---| |---| | |---| |
|----| | | | P | | P | | | |----|
| PE1 |---| |-----| |-----| PE2 |
| | | | | | | |
| | |---| |---| | |
|-----| |-----|
| |
\ /
--------------------------
Figure 1. Model of Operation for RSVP-based admission control over
MPLS/BGP VPN
To establish a unidirectional reservation for a point-to-point flow
from Sender to Receiver that takes account of resource availability
on the CE-PE and PE-CE links only, the following steps need to take
place:
1. Sender sends a Path message to an IP address of the Receiver.
2. Path message is processed by CE1 using normal RSVP procedures
and forwarded towards the Receiver along the link CE1-PE1.
3. PE1 processes Path message and forwards towards the Receiver
across the provider backbone.
4. PE2 processes Path message and forwards towards the Receiver
along link PE2-CE2.
5. CE2 processes Path message using normal RSVP procedures and
forwards towards Receiver.
6. Receiver sends Resv message to CE2.
7. CE2 sends Resv message to PE2.
8. PE2 processes Resv message (including performing admission
control on link PE2-CE2) and sends Resv to PE1.
9. PE1 processes Resv message and sends Resv to CE1.
10. CE1 processes Resv using normal RSVP procedures, performs
admission control on the link CE1-PE1 and sends Resv message to
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Sender if successful.
In each of the steps involving Resv messages (6 through 10) the node
sending the Resv uses the previously established Path state to
determine the "RSVP Previous Hop (PHOP)" and sends a Resv message to
that address. We note that establishing that Path state correctly at
PEs is one of the challenges posed by the BGP/MPLS environment.
3. Admission Control on PE-CE Links
In the following sections we trace through the steps outlined in
Section 2.1 and expand on the details for those steps where standard
RSVP procedures need to be extended or modified to support the BGP/
MPLS VPN environment. For all the remaining steps described in the
preceding section, standard RSVP processing rules apply.
All the procedures described below support both IPv4 and IPv6
addressing. In all cases where IPv4 is referenced, IPv6 can be
substituted with identical procedures and results. Object
definitions for both IPv4 and IPv6 are provided in Section 8.
3.1. New Objects of Type VPN-IPv4
For RSVP signaling within a VPN, certain RSVP objects need to be
extended. Since customer IP addresses need not be unique, the
current types of SESSION, SENDER_TEMPLATE and FILTERSPEC objects are
no longer sufficient to globally identify RSVP states in P/PE
routers, since those are currently based on IP addresses. We propose
new types of SESSION, SENDER_TEMPLATE and FILTERSPEC objects, which
contain globally unique VPN-IPv4 format addresses. The ingress and
egress PE nodes translate between the regular IPv4 addresses for
messages to and from the CE, and VPN-IPv4 addresses for messages to
and from PE routers. The rules for this translation are described in
later sections.
The RSVP_HOP object in a RSVP message currently specifies an IP
address to be used by the neighboring RSVP hop to reply to the
message sender. However, MPLS VPN PE routers (especially those
separated by Option-B Autonomous System Border Routers -ASBRs) are
not required to have direct IP reachability to each other. To solve
this issue, we propose the use of label switching to forward RSVP
messages between nodes within a MPLS VPN. This is achieved by
defining a new VPN-IPv4 RSVP_HOP object. Use of the VPN-IPv4
RSVP_HOP object enables any two adjacent RSVP hops in a MPLS VPN
(e.g. a PE in AS 1 and a PE in AS2) to correctly identify each other
and send RSVP messages directly to each other.
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The VPN-IPv4 RSVP_HOP object carries the IPv4 address of the message
sender and a Logical Interface Handle (LIH) as before, but in
addition carries a VPN-IPv4 address which also represents the sender
of the message. The message sender MUST also advertise this VPN-IPv4
address into BGP, associated with a locally allocated label, and this
advertisement MUST be propagated by BGP throughout the VPN and to
adjacent ASes if required to provide reachability to this PE. Frames
received by the PE marked with this label MUST be given to the local
control plane for processing. When a neighboring RSVP hop wishes to
reply to a message carrying a VPN-IPv4 RSVP_HOP, it looks for a BGP
advertisement of the VPN-IPv4 address contained in that RSVP_HOP. If
this address is found and carries an associated label, the
neighboring RSVP node MUST encapsulate the RSVP message with this
label and send it via MPLS encapsulation to the BGP next-hop
associated with the route. The destination IP address of the message
is taken from the IP address field of the RSVP_HOP object, as
described in [RFC2205]. Additionally, the IPv4 address in the
RSVP_HOP object continues to be used for all other existing purposes,
including neighbor matching between Path/Resv and SRefresh messages
([RFC2961]), authentication ([RFC2747]), etc.
The VPN-IPv4 address used in the VPN-IPv4 RSVP_HOP object MAY
represent an existing address in the VRF that corresponds to the flow
(e.g. a local loopback or PE-CE link address within the VRF for this
customer), or MAY be created specially for this purpose. In the case
where the address is specially created for RSVP signaling (and
possibly other control protocols), the BGP advertisement MUST NOT be
redistributed to, or reachable by, any CEs outside the MPLS VPN. One
way to achieve this is by creating a special "control protocols VPN"
with VRF state on every PE/ASBR, carrying route targets not imported
into customer VRFs. In the case where a customer VRF address is used
as the VPN-IPv4 address, a VPN-IPv4 address in one customer VRF MUST
NOT be used to signal RSVP messages for a flow in a different VRF.
If a PE/ASBR is sending a Path message to another PE/ASBR within the
VPN, and it has any appropriate VPN-IPv4 address for signaling that
satisfies the requirements outlined above, it MUST use a VPN-IPv4
RSVP_HOP object with this address for all RSVP messages within the
VPN. If a PE/ASBR does not have any appropriate VPN-IPv4 address to
use for signaling, it MAY send the Path message with a regular IPv4
RSVP_HOP object. In this case, the reply will be IP encapsulated.
This option is not preferred because there is no guarantee that the
neighboring RSVP hop has IP reachability to the sending node. If a
PE/ASBR receives or originates a Path message with a VPN-IPv4
RSVP_HOP object, any RSVP_HOP object in corresponding upstream
messages for this flow (e.g. Resv, ResvTear) or downstream messages
(e.g. ResvError, PathTear) sent by this node within the VPN MUST be
a VPN-IPv4 RSVP_HOP.
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3.2. Path Message Processing at Ingress PE
When a Path message arrives at the ingress PE (step 3 of Section 2.1)
the PE needs to establish suitable Path state and forward the Path
message on to the egress PE. In the following paragraphs we
described the steps taken by the ingress PE.
The Path message is addressed to the eventual destination (the
receiver at the remote customer site) and carries the IP router alert
option, in accordance with [RFC2205]. The ingress PE MUST recognize
the router alert option, intercept these messages and process them as
RSVP signaling messages.
As noted above, there is an issue in recognizing Path messages as
they arrive at the egress PE (PE 2 in Figure 1). The approach
defined here is to address the Path messages sent by the ingress PE
directly to the egress PE, and send it without IP router alert
option; that is, rather than using the ultimate receiver's
destination address as the destination address of the Path message,
we use the loopback address of the egress PE as the destination
address of the Path message. This approach has the advantage that it
does not require any new data plane capabilities for the egress PE
beyond those of a standard BGP/MPLS VPN PE. Details of the
processing of this message at the egress PE are described below in
Section 3.3. The approach of addressing a Path message directly to
an RSVP next hop (that may or may not be the next IP hop) is already
used in other environments such as those of [RFC4206] and [RFC4804].
The details of operation at the ingress PE are as follows. When the
ingress PE (PE1 in Figure 1) receives a Path message from CE1 that is
addressed to the receiver, the VRF that is associated with the
incoming interface is identified, just as for normal data path
operations. The Path state for the session is stored, and is
associated with that VRF, so that potentially overlapping addresses
among different VPNs do not appear to belong to the same session.
The destination address of the receiver is looked up in the
appropriate VRF, and the BGP Next-Hop for that destination is
identified. That next-hop is the egress PE (PE2 in Figure 1). A new
VPN-IPv4 SESSION object is constructed, containing the Route
Distinguisher (RD) that is part of the VPN-IPv4 route prefix for this
destination, and the IPv4 address from the SESSION. In addition, a
new VPN-IPv4 SENDER_TEMPLATE object is constructed, with the original
IPv4 address from the incoming SENDER_TEMPLATE plus the RD that is
used by this PE to advertise that prefix for this customer into the
VPN. A new Path message is constructed with a destination address
equal to the address of the egress PE identified above. This new
Path message will contain all the objects from the original Path
message, replacing the original SESSION and SENDER_TEMPLATE objects
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with the new VPN-IPv4 type objects. The Path message is sent without
router alert option and contains a RSVP_HOP object constructed as
specified in Section 3.1.
3.3. Path Message Processing at Egress PE
When a Path message arrives at the egress PE, (step 4 of Section 2.1)
it is addressed to the PE itself, and is handed to RSVP for
processing. The router extracts the RD and IPv4 address from the
VPN-IPv4 SESSION object, and determines the local VRF context by
finding a matching VPN-IPv4 prefix with the specified RD that has
been advertised by this router into BGP. The entire incoming RSVP
message, including the VRF information, is stored as part of the Path
state.
Now the RSVP module can construct a Path message which differs from
the Path it received in the following ways:
a. Its destination address is the IP address extracted from the
SESSION Object;
b. The SESSION and SENDER_TEMPLATE objects are converted back to
IPv4-type by discarding the attached RD
c. The RSVP_HOP Object contains the IP address of the outgoing
interface of the egress PE and a Logical Interface Handle (LIH),
as per normal RSVP processing.
The router then sends the Path message on towards its destination
over the interface identified above. This Path message carries the
router alert option as required by [RFC2205].
3.4. Resv Processing at Egress PE
When a receiver at the customer site originates a Resv message for
the session, normal RSVP procedures apply until the Resv, making its
way back towards the sender, arrives at the "egress" PE (step 8 of
Section 2.1). Note that this is the "egress" PE with respect to the
direction of data flow, i.e. PE2 in figure 1. On arriving at PE2,
the SESSION and FILTER_SPEC objects in the Resv, and the VRF in which
the Resv was received, are used to find the matching Path state
stored previously. At this stage, admission control can be performed
on the PE-CE link.
Assuming admission control is successful, the PE constructs a Resv
message to send to the RSVP HOP stored in the Path state, i.e., the
ingress PE (PE1 in Figure 1). The IPv4 SESSION object is replaced
with the same VPN-IPv4 SESSION object received in the Path. The IPv4
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FILTER_SPEC object is replaced with a VPN-IPv4 FILTER_SPEC object,
which copies the VPN-IPv4 address from the SENDER_TEMPLATE received
in the matching Path message. The RSVP_HOP in the Resv message MUST
be constructed as specified in Section 3.1. The Resv message MUST be
addressed to the IP address contained within the RSVP_HOP object in
the Path message. If the Path message contained a VPN-IPv4 RSVP_HOP
object, the Resv MUST be MPLS-encapsulated using the label associated
with that VPN-IPv4 address in BGP, as described in Section 3.1. If
the Path message contained an IPv4 RSVP_HOP object, the Resv is
simply IP-encapsulated and addressed directly to the IP address in
the RSVP_HOP object.
If admission control is not successful on the egress PE, a ResvError
message is sent towards the receiver as per normal RSVP processing.
3.5. Resv Processing at Ingress PE
Upon receiving a Resv message at the ingress PE (step 8 of
Section 2.1) with respect to data flow (i.e. PE1 in Figure 1), the
PE determines the local VRF context and associated Path state for
this Resv by decoding the received SESSION and FILTER_SPEC objects.
It is now possible to generate a Resv message to send to the
appropriate CE. The Resv message sent to the ingress CE will contain
IPv4 SESSION and FILTER_SPEC objects, derived from the appropriate
Path state. Since we assume in this section that admission control
over the Provider's backbone is not needed, the ingress PE does not
perform any admission control for this reservation.
3.6. Other RSVP Messages
Processing of PathError, PathTear, ResvError, ResvTear and ResvConf
messages is generally straightforward and follows the rules of
[RFC2205]. These additional rules MUST be observed for messages
transmitted within the VPN (i.e. Between the PEs):
o The SESSION, SENDER_TEMPLATE and FILTER_SPEC objects MUST be
converted from IPv4 to VPN-IPv4 form and back in the same manner
as described above for Path and Resv messages.
o The appropriate type of RSVP_HOP object (VPN-IPv4 or IPv4) MUST be
used as described above.
o Depending on the type of RSVP_HOP object received from the
neighbor, the message MUST be MPLS-encapsulated or IP-encapsulated
as described above.
o The matching state & VRF MUST be determined by decoding the RD and
IPv4 addresses in the SESSION and FILTER_SPEC objects.
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o The message MUST be directly addressed to the appropriate PE,
without using the router alert option.
4. Admission Control in Provider's Backbone
The preceding section outlines how per-customer reservations can be
made over the PE-CE links. This may be sufficient in many situations
where the backbone is well engineered with ample capacity and there
is no need to perform any sort of admission control in the backbone.
However, in some cases where excess capacity cannot be relied upon
(e.g., during failures or unanticipated periods of overload) it may
be desirable to be able to perform admission control in the backbone
on behalf of customer traffic.
Because of the fact that routes to customer addresses are not present
in the P routers, along with the concerns of scalability that would
arise if per-customer reservations were allowed in the P routers, it
is clearly necessary to map the per-customer reservations described
in the preceding section onto some sort of aggregate reservations.
Furthermore, customer data packets need to be tunneled across the
provider backbone just as in normal BGP/MPLS VPN operation.
Given these considerations, a feasible way to achieve the objective
of admission control in the backbone is to use the ideas described in
[RFC4804]. MPLS-TE tunnels can be established between PEs as a means
to perform aggregate admission control in the backbone.
An MPLS-TE tunnel from an ingress PE to an egress PE can be thought
of as a virtual link of a certain capacity. The main change to the
procedures described above is that when a Resv is received at the
ingress PE, an admission control decision can be performed by
checking whether sufficient capacity of that virtual link remains
available to admit the new customer reservation. We note also that
[RFC4804] uses the IF_ID RSVP_HOP object to identify the tunnel
across the backbone, rather than the simple RSVP_HOP object described
in Section 3.2. The procedures of [RFC4804] should be followed here
as well.
To achieve effective admission control in the backbone, there needs
to be some way to separate the data plane traffic that has a
reservation from that which does not. We assume that packets that
are subject to admission control on the core will be given a
particular MPLS EXP value, and that no other packets will be allowed
to enter the core with this value unless they have passed admission
control. Some fraction of link resources will be allocated to queues
on core links for packets bearing that EXP value, and the MPLS-TE
tunnels will use that resource pool to make their constraint-based
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routing and admission control decisions. This is all consistent with
the principles of aggregate RSVP reservations described in [RFC3175].
5. Inter-AS operation
[RFC4364] defines three modes of inter-AS operation for MPLS/BGP
VPNs, referred to as options A, B and C. In the following sections we
describe how the scheme described above can operate in each inter-AS
environment.
5.1. Inter-AS Option A
Operation of RSVP in Inter-AS Option A is quite straightforward.
Each ASBR operates like a PE, and the ASBR-ASBR links can be viewed
as PE-CE links in terms of admission control. If the procedures
defined in Section 3 are enabled on both ASBRs, then admission
control may be performed on the inter-ASBR links. In addition, the
operator of each AS can independently decide whether or not to
perform admission control across his backbone. The new objects
described in this document MUST NOT be sent in any RSVP message
between two Option-A ASBRs.
5.2. Inter-AS Option B
To support inter-AS Option B, we require some additional processing
of RSVP messages on the ASBRs. Recall that, when packets are
forwarded from one AS to another in option B, the VPN label is
swapped by each ASBR as a packet goes from one AS to another. The
BGP next hop seen by the ingress PE will be the ASBR, and there need
not be IP visibility between the ingress and egress PEs. Hence when
the ingress PE sends the Path message to the BGP next hop of the VPN-
IPv4 route towards the destination, it will be received by the ASBR.
The ASBR determines the next hop of the route in a similar way as the
ingress PE - by finding a matching BGP VPN-IPv4 route with the same
RD and a matching prefix.
The provider(s) who interconnect ASes using option B may or may not
desire to perform admission control on the inter-AS links. This
choice affects the detailed operation of ASBRs. We describe the two
modes of operation - with and without admission control at the ASBRs
- in the following sections.
5.2.1. Admission control on ASBR
In this scenario, the ASBR performs full RSVP signaling and admission
control. The RSVP database is indexed on the ASBR using the VPN-IPv4
SESSION, SENDER_TEMPLATE and FILTER_SPEC objects (which uniquely
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identify RSVP sessions and flows as per the requirements of
[RFC2205]). These objects are forwarded unmodified in both
directions by the ASBR. All other procedures of RSVP are performed
as if the ASBR was a RSVP hop. In particular, the RSVP_HOP objects
sent in Path and Resv messages contain IP addresses of the ASBR,
which MUST be reachable by the neighbor to whom the message is being
sent. Note that since the VPN-IPv4 SESSION, SENDER_TEMPLATE and
FILTER_SPEC objects satisfy the uniqueness properties required for a
RSVP database implementation as per [RFC2209], no customer VRF
awareness is required on the ASBR.
5.2.2. No admission control on ASBR
If the ASBR is not doing admission control, it is desirable that per-
flow state not be maintained on the ASBR. This requires adjacent
RSVP hops (i.e. The ingress and egress PEs of the respective ASes)
to send RSVP messages directly between them. This is only possible
if they are MPLS-encapsulated. The use of the VPN-IPv4 RSVP_HOP
object described in Section 3.1 is REQUIRED in this case.
When an ASBR that is not installing local RSVP state receives a Path
message, it looks up the next-hop of the matching BGP route as
described in Section 3.2, and sends the Path message to the next-hop,
without modifying any RSVP objects (including the RSVP_HOP). This
process is repeated at subsequent ASBRs until the Path message
arrives at a router that is installing local RSVP state (either the
ultimate egress PE, or an ASBR configured to perform admission
control). This router receives the Path and processes it as
described in Section 3.3 if it is a PE, or Section 5.2.1 if it is an
ASBR performing admission control. When this router sends the Resv
upstream, it looks up the routing table for a next-hop+label for the
VPN-IPv4 address in the PHOP, encapsulates the Resv with that label
and sends it upstream. This message will be received for control
processing directly on the upstream RSVP hop (that last updated the
RSVP_HOP field in the Path message), without any involvement of
intermediate ASBRs.
The ASBR is not expected to process any other RSVP messages apart
from the Path message as described above. The ASBR also does not
need to store any RSVP state. Note that any ASBR along the path that
wishes to do admission control or insert itself into the RSVP
signaling flow, may do so by writing its own RSVP_HOP object with
IPv4 and VPN-IPv4 address pointing to itself.
If an Option-B ASBR receives a RSVP Path message with an IPv4
RSVP_HOP, does not wish to perform admission control but is willing
to install local state for this flow, the ASBR MUST process and
forward RSVP signaling messages for this flow as described in
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Section 5.2.1 (with the exception that it does not perform admission
control). If an Option-B ASBR receives a RSVP Path message with an
IPv4 RSVP_HOP, but does not wish to install local state or perform
admission control for this flow, the ASBR MUST NOT forward the Path
message. In addition, the ASBR SHOULD send a PathError message of
Error Code "RSVP over MPLS Problem" and Error Value "RSVP_HOP not
reachable across VPN" (see Section 9) signifying to the upstream RSVP
hop that the supplied RSVP_HOP object is insufficient to provide
reachability across this VPN. This failure condition is not expected
to be recoverable.
5.3. Inter-AS Option C
Operation of RSVP in Inter-AS Option C is also quite straightforward,
because there exists an LSP directly from ingress PE to egress PE.
In this case, there is no significant difference in operation from
the single AS case described in Section 3. Furthermore, if it is
desired to provide admission control from PE to PE, it can be done by
building an inter-AS TE tunnel and then using the procedures
described in Section 4.
6. Operation with RSVP disabled
It is often the case that RSVP will not be enabled on the PE-CE
links. In such an environment, a customer may reasonably expect that
RSVP messages sent into the L3 VPN network should be forwarded just
like any other IP datagrams. This transparency is useful when the
customer wishes to use RSVP within his own sites or perhaps to
perform admission control on the CE-PE links (in CE->PE direction
only), without involvement of the PEs. For this reason, a PE SHOULD
NOT discard or modify RSVP messages sent towards it from a CE when
RSVP is not enabled on the PE-CE links. Similarly a PE SHOULD NOT
discard or modify RSVP messages which are destined for one of its
attached CEs, even when RSVP is not enabled on those links. Note
that the presence of the router alert option in some RSVP messages
may cause them to be forwarded outside of the normal forwarding path,
but that the guidance of this paragraph still applies in that case.
Note also that this guidance applies regardless of whether RSVP-TE is
used in some, all, or none of the L3VPN network.
7. Other RSVP procedures
This section describes modifications to other RSVP procedures
introduced by MPLS VPNs
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7.1. Refresh overhead reduction
The following points ought to be noted regarding RSVP refresh
overhead reduction ([RFC2961]) across a MPLS VPN:
o The hop between the ingress and egress PE of a VPN is to be
considered as traversing one or more non-RSVP hops. As such, the
procedures described in Section 5.3 of [RFC2961] relating to non-
RSVP hops SHOULD be followed.
o The source IP address of a SRefresh message MUST match the IPv4
address signalled in the RSVP_HOP object contained in the
corresponding Path or Resv message. The IPv4 address in any
received VPN-IPv4 RSVP_HOP object MUST be used as the source
address of that message for this purpose.
7.2. Cryptographic Authentication
The following points ought to be noted regarding RSVP cryptographic
authentication ([RFC2747]) across a MPLS VPN:
o The IPv4 address in any received VPN-IPv4 RSVP_HOP object MUST be
used as the source address of that message for purposes of
identifying the security association.
o Forwarding of Challenge and Response messages MUST follow the same
rules as described above for hop-by-hop messages. Specifically,
if the originator of a Challenge/Response message has received a
VPN-IPv4 RSVP_HOP object from the corresponding neighbor, it MUST
use the label associated with that VPN-IPv4 address in BGP to
forward the Challenge/Response message.
7.3. RSVP Aggregation
[RFC3175] and [RFC4860] describe mechanisms to aggregate multiple
individual RSVP reservations into a single larger reservation on the
basis of a common DSCP/PHB for traffic classification. The following
points ought to be noted in this regard:
o The procedures described in this section apply only in the case
where the Aggregator and Deaggregator nodes are C/CE devices, and
the entire MPLS VPN lies within the Aggregation Region. The case
where the PE is also an Aggregator/Deaggregator is more complex
and not considered in this document.
o Support of Aggregate RSVP sessions is OPTIONAL. When supported:
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* Aggregate RSVP sessions MUST be treated in the same way as
regular IPv4 RSVP sessions. To this end, all the procedures
described in Section 3 and Section 4 MUST be followed for
aggregate RSVP sessions. The corresponding new SESSION,
SENDER_TEMPLATE and FILTERSPEC objects are defined in
Section 8.
* End-To-End (E2E) RSVP sessions are passed unmodified through
the MPLS VPN. These RSVP messages SHOULD be identified by
their IP protocol (RSVP-E2E-IGNORE, 134). When the ingress PE
receives any RSVP message with this IP protocol, it MUST
process this frame as if it is regular customer traffic and
ignore any router alert option. The appropriate VPN and
transport labels are applied to the frame and it is forwarded
towards the remote CE. Note that this message will not be
received or processed by any other P or PE node.
* Any SESSION-OF-INTEREST object (defined in [RFC4860]) MUST be
conveyed unmodified across the MPLS VPN.
7.4. Support for CE-CE RSVP-TE
[I-D.ietf-l3vpn-e2e-rsvp-te-reqts] describes a set of requirements
for the establishment for CE-CE MPLS LSPs across networks offering an
L3VPN service. The requirements specified in that document are
similar to those addressed by this document, in that both address the
issue of handling RSVP requests from customers in a VPN context. It
is possible that the solution described here could be adapted to meet
the requirements of [I-D.ietf-l3vpn-e2e-rsvp-te-reqts]. To the
extent that this document uses signaling extensions described in
[RFC3473] which have already been used for GMPLS/TE, we expect that
CE-CE RSVP/TE will be incremental work built on these extensions.
These extensions will be considered in a separate document.
8. Object Definitions
8.1. VPN-IPv4 and VPN-IPv6 SESSION objects
The usage of the VPN-IPv4 (or VPN-IPv6) SESSION Object is described
in Section 3.2 to Section 3.6. The VPN-IPv4 (or VPN-IPv6) SESSION
object appears in RSVP messages that ordinarily contain a SESSION
object and are sent between ingress PE and egress PE in either
direction. The object MUST NOT be included in any RSVP messages that
are sent outside of the provider's backbone (except in the inter-AS
option B and C cases, as described above, when it may appear on
inter-AS links).
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The VPN-IPv6 SESSION object is analogous to the VPN-IPv4 SESSION
object, using an VPN-IPv6 address ([RFC4659]) instead of an VPN-IPv4
address ([RFC4364]).
The formats of the objects are as follows:
o VPN-IPv4 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 DestAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
o VPN-IPv6 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 DestAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
The VPN-IPv4 DestAddress (respectively VPN-IPv6 DestAddress) field
contains an address of the VPN-IPv4 (respectively VPN-IPv6) address
family encoded as specified in [RFC4364] (respectively [RFC4659]).
The content of this field is discussed in Section 3.2 and
Section 3.3.
The protocol ID, flags, and DstPort are identical to the same fields
in the IPv4 and IPv6 SESSION objects ([RFC2205]).
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8.2. VPN-IPv4 and VPN-IPv6 SENDER_TEMPLATE objects
The usage of the VPN-IPv4 (or VPN-IPv6) SENDER_TEMPLATE Object is
described in Section 3.2 and Section 3.3. The VPN-IPv4 (or VPN-IPv6)
SENDER_TEMPLATE object appears in RSVP messages that ordinarily
contain a SENDER_TEMPLATE object and are sent between ingress PE and
egress PE in either direction (such as Path, PathError, and
PathTear). The object MUST NOT be included in any RSVP messages that
are sent outside of the provider's backbone (except in the inter-AS
option B and C cases, as described above, when it may appear on
inter-AS links). The format of the object is as follows:
o VPN-IPv4 SENDER_TEMPLATE object: Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 SrcAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Reserved | SrcPort |
+-------------+-------------+-------------+-------------+
o VPN-IPv6 SENDER_TEMPLATE object: Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 SrcAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Reserved | SrcPort |
+-------------+-------------+-------------+-------------+
The VPN-IPv4 SrcAddress (respectively VPN-IPv6 SrcAddress) field
contains an address of the VPN-IPv4 (respectively VPN-IPv6) address
family encoded as specified in [RFC4364] (respectively [RFC4659]).
The content of this field is discussed in Section 3.2 and
Section 3.3.
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The SrcPort is identical to the SrcPort field in the IPv4 and IPv6
SENDER_TEMPLATE objects ([RFC2205]).
The Reserved field MUST be set to zero on transmit and ignored on
receipt.
8.3. VPN-IPv4 and VPN-IPv6 FILTER_SPEC objects
The usage of the VPN-IPv4 (or VPN-IPv6) FILTER_SPEC Object is
described in Section 3.4 and Section 3.5. The VPN-IPv4 (or VPN-IPv6)
FILTER_SPEC object appears in RSVP messages that ordinarily contain a
FILTER_SPEC object and are sent between ingress PE and egress PE in
either direction (such as Resv, ResvError, and ResvTear). The object
MUST NOT be included in any RSVP messages that are sent outside of
the provider's backbone (except in the inter-AS option B and C cases,
as described above, when it may appear on inter-AS links).
o VPN-IPv4 FILTER_SPEC object: Class = 10, C-Type = TBA
Definition same as VPN-IPv4 SENDER_TEMPLATE object.
o VPN-IPv6 FILTER_SPEC object: Class = 10, C-Type = TBA
Definition same as VPN-IPv6 SENDER_TEMPLATE object.
The content of the VPN-IPv4 SrcAddress (or VPN-IPv6 SrcAddress) field
is discussed in Section 3.4 and Section 3.5.
The SrcPort is identical to the SrcPort field in the IPv4 and IPv6
SENDER_TEMPLATE objects ([RFC2205]).
The Reserved field MUST be set to zero on transmit and ignored on
receipt.
8.4. VPN-IPv4 and VPN-IPv6 RSVP_HOP objects
Usage of the VPN-IPv4 (or VPN-IPv6) RSVP_HOP Object is described in
Section 3.1 and Section 5.2.2. The VPN-IPv4 (VPN-IPv6) RSVP_HOP
object is used to establish signaling reachability between RSVP
neighbors separated by one or more Option-B ASBRs. This object may
appear in RSVP messages that carry a RSVP_HOP object, and that travel
between the Ingress and Egress PEs. It MUST NOT be included in any
RSVP messages that are sent outside of the provider's backbone
(except in the inter-AS option B and C cases, as described above,
when it may appear on inter-AS links). The format of the object is
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as follows:
o VPN-IPv4 RSVP_HOP object: Class = 3, C-Type = TBA
+-------------+-------------+-------------+-------------+
| IPv4 Next/Previous Hop Address (4 bytes) |
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 Next/Previous Hop Address (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Logical Interface Handle |
+-------------+-------------+-------------+-------------+
o VPN-IPv6 RSVP_HOP object: Class = 3, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 Next/Previous Hop Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 Next/Previous Hop Address (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Logical Interface Handle |
+-------------+-------------+-------------+-------------+
The IPv4 Next/Previous Hop Address, IPv6 Next/Previous Hop Address
and the Logical Interface Handle fields are identical to those of the
RSVP_HOP object ([RFC2205]).
The VPN-IPv4 Next/Previous Hop Address (respectively VPN-IPv6 Next/
Previous Hop Address) field contains an address of the VPN-IPv4
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(respectively VPN-IPv6) address family encoded as specified in
[RFC4364] (respectively [RFC4659]). The content of this field is
discussed in Section 3.1.
8.5. Aggregated VPN-IPv4 and VPN-IPv6 SESSION objects
The usage of Aggregated VPN-IPv4 (or VPN-IPv6) SESSION object is
described in Section 7.3. The AGGREGATE-VPN-IPv4 (respectively
AGGREGATE-IPv6-VPN) SESSION object appears in RSVP messages that
ordinarily contain a AGGREGATE-IPv4 (respectively AGGREGATE-IPv6)
SESSION object as defined in [RFC3175] and are sent between ingress
PE and egress PE in either direction. The GENERIC-AGGREGATE-VPN-IPv4
(respectively AGGREGATE-VPN-IPv6) SESSION object should appear in all
RSVP messages that ordinarily contain a GENERIC-AGGREGATE-IPv4
(respectively GENERIC-AGGREGATE-IPv6) SESSION object as defined in
[RFC4860] and are sent between ingress PE and egress PE in either
direction. These objects MUST NOT be included in any RSVP messages
that are sent outside of the provider's backbone (except in the
inter-AS option B and C cases, as described above, when it may appear
on inter-AS links). The processing rules for these objects are
otherwise identical to those of the VPN-IPv4 (respectively VPN-IPv6)
SESSION object defined in Section 8.1. The format of the object is
as follows:
o AGGREGATE-VPN-IPv4 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 DestAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Reserved | Flags | Reserved | DSCP |
+-------------+-------------+-------------+-------------+
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o AGGREGATE-VPN-IPv6 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 DestAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Reserved | Flags | Reserved | DSCP |
+-------------+-------------+-------------+-------------+
The VPN-IPv4 DestAddress (respectively VPN-IPv6 DestAddress) field
contains an address of the VPN-IPv4 (respectively VPN-IPv6) address
family encoded as specified in [RFC4364] (respectively [RFC4659]).
The content of this field is discussed in Section 3.2 and
Section 3.3.
The flags and DSCP are identical to the same fields of the AGGREGATE-
IPv4 and AGGREGATE-IPv6 SESSION objects ([RFC3175]).
The Reserved field MUST be set to zero on transmit and ignored on
receipt.
o GENERIC-AGGREGATE-VPN-IPv4 SESSION object:
Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 DestAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Reserved | Flags | PHB-ID |
+-------------+-------------+-------------+-------------+
| Reserved | vDstPort |
+-------------+-------------+-------------+-------------+
| Extended vDstPort |
+-------------+-------------+-------------+-------------+
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o GENERIC-AGGREGATE-VPN-IPv6 SESSION object:
Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 DestAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Reserved | Flags | PHB-ID |
+-------------+-------------+-------------+-------------+
| Reserved | vDstPort |
+-------------+-------------+-------------+-------------+
| Extended vDstPort |
+-------------+-------------+-------------+-------------+
The VPN-IPv4 DestAddress (respectively VPN-IPv6 DestAddress) field
contains an address of the VPN-IPv4 (respectively VPN-IPv6) address
family encoded as specified in [RFC4364] (respectively [RFC4659]).
The content of this field is discussed in Section 3.2 and
Section 3.3.
The flags, PHB-ID, vDstPort and Extended vDstPort are identical to
the same fields of the GENERIC-AGGREGATE-IPv4 and GENERIC-AGGREGATE-
IPv6 SESSION objects ([RFC4860]).
The Reserved field MUST be set to zero on transmit and ignored on
receipt.
8.6. AGGREGATE-VPN-IPv4 and AGGREGATE-VPN-IPv6 SENDER_TEMPLATE objects
The usage of Aggregated VPN-IPv4 (or VPN-IPv6) SENDER_TEMPLATE object
is described in Section 7.3. The AGGREGATE-VPN-IPv4 (respectively
AGGREGATE-VPN-IPv6) SENDER_TEMPLATE object appears in RSVP messages
that ordinarily contain a AGGREGATE-IPv4 (respectively AGGREGATE-
IPv6) SENDER_TEMPLATE object as defined in [RFC3175] and [RFC4860],
and are sent between ingress PE and egress PE in either direction.
These objects MUST NOT be included in any RSVP messages that are sent
outside of the provider's backbone (except in the inter-AS option B
and C cases, as described above, when it may appear on inter-AS
links). The processing rules for these objects are otherwise
identical to those of the VPN-IPv4 (respectively VPN-IPv6)
SENDER_TEMPLATE object defined in Section 8.2. The format of the
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object is as follows:
o AGGREGATE-VPN-IPv4 SENDER_TEMPLATE object:
Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 AggregatorAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
o AGGREGATE-VPN-IPv6 SENDER_TEMPLATE object:
Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 AggregatorAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
The VPN-IPv4 AggregatorAddress (respectively VPN-IPv6
AggregatorAddress) field contains an address of the VPN-IPv4
(respectively VPN-IPv6) address family encoded as specified in
[RFC4364] (respectively [RFC4659]). The content and processing rules
for these objects are similar to those of the VPN-IPv4
SENDER_TEMPLATE object defined in Section 8.2.
The flags and DSCP are identical to the same fields of the AGGREGATE-
IPv4 and AGGREGATE-IPv6 SESSION objects.
8.7. AGGREGATE-VPN-IPv4 and AGGREGATE-VPN-IPv6 FILTER_SPEC objects
The usage of Aggregated VPN-IPv4 FILTER_SPEC object is described in
Section 7.3. The AGGREGATE-VPN-IPv4 FILTER_SPEC object appears in
RSVP messages that ordinarily contain a AGGREGATE-IPv4 FILTER_SPEC
object as defined in [RFC3175] and [RFC4860], and are sent between
ingress PE and egress PE in either direction. These objects MUST NOT
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be included in any RSVP messages that are sent outside of the
provider's backbone (except in the inter-AS option B and C cases, as
described above, when it may appear on inter-AS links). The
processing rules for these objects are otherwise identical to those
of the VPN-IPv4 FILTER_SPEC object defined in Section 8.3. The
format of the object is as follows:
o AGGREGATE-VPN-IPv4 FILTER_SPEC object:
Class = 10, C-Type = TBA
Definition same as AGGREGATE-VPN-IPv4 SENDER_TEMPLATE object.
o AGGREGATE-VPN-IPv6 FILTER_SPEC object:
Class = 10, C-Type = TBA
Definition same as AGGREGATE-VPN-IPv6 SENDER_TEMPLATE object.
9. IANA Considerations
Section 8 defines new objects. Therefore, this document requests
IANA to modify the RSVP parameters registry, 'Class Names, Class
Numbers, and Class Types' subregistry, and:
o assign six new C-Types under the existing SESSION Class (Class
number 1), as suggested below:
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Class
Number Class Name Reference
------ ----------------------- ---------
1 SESSION [RFC2205]
Class Types or C-Types:
.. ... ...
aa VPN-IPv4 [RFCXXXX]
bb VPN-IPv6 [RFCXXXX]
cc AGGREGATE-VPN-IPv4 [RFCXXXX]
dd AGGREGATE-VPN-IPv6 [RFCXXXX]
ee GENERIC-AGGREGATE-VPN-IPv4 [RFCXXXX]
ff GENERIC-AGGREGATE-VPN-IPv6 [RFCXXXX]
[Note to IANA and the RFC Editor: Please replace RFCXXXX with the RFC
number of this specification. Suggested values: aa-ff=19-24]
o assign four new C-Types under the existing SENDER_TEMPLATE Class
(Class number 11), as suggested below:
Class
Number Class Name Reference
------ ----------------------- ---------
11 SENDER_TEMPLATE [RFC2205]
Class Types or C-Types:
.. ... ...
aa VPN-IPv4 [RFCXXXX]
bb VPN-IPv6 [RFCXXXX]
cc AGGREGATE-VPN-IPv4 [RFCXXXX]
dd AGGREGATE-VPN-IPv6 [RFCXXXX]
[Note to IANA and the RFC Editor: Please replace RFCXXXX with the RFC
number of this specification. Suggested values: aa-dd=14-17]
o assign four new C-Types under the existing FILTER_SPEC Class
(Class number 10), as suggested below:
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Class
Number Class Name Reference
------ ----------------------- ---------
10 FILTER_SPEC [RFC2205]
Class Types or C-Types:
.. ... ...
aa VPN-IPv4 [RFCXXXX]
bb VPN-IPv6 [RFCXXXX]
cc AGGREGATE-VPN-IPv4 [RFCXXXX]
dd AGGREGATE-VPN-IPv6 [RFCXXXX]
[Note to IANA and the RFC Editor: Please replace RFCXXXX with the RFC
number of this specification. Suggested values: aa-dd=14-17]
o assign two new C-Types under the existing RSVP_HOP Class (Class
number 3), as suggested below:
Class
Number Class Name Reference
------ ----------------------- ---------
3 RSVP_HOP [RFC2205]
Class Types or C-Types:
.. ... ...
aa VPN-IPv4 [RFCXXXX]
bb VPN-IPv6 [RFCXXXX]
[Note to IANA and the RFC Editor: Please replace RFCXXXX with the RFC
number of this specification. Suggested values: aa-bb=5-6]
In addition, a new PathError code/value is required to identify a
signaling reachability failure and the need for a VPN-IPv4 or VPN-
IPv6 RSVP_HOP object as described in Section 5.2.2. Therefore, this
document requests IANA to modify the RSVP parameters registry, 'Error
Codes and Globally-Defined Error Value Sub-Codes' subregistry, and:
o assign a new Error Code and sub-code, as suggested below:
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aa RSVP over MPLS Problem [RFCXXXX]
This Error Code has the following globally-defined Error
Value sub-codes:
1 = RSVP_HOP not reachable across VPN [RFCXXXX]
[Note to IANA and the RFC Editor: Please replace RFCXXXX with the RFC
number of this specification. Suggested values: aa=34]
10. Security Considerations
[RFC4364] addresses the security considerations of BGP/MPLS VPNs in
general. General RSVP security considerations are discussed in
[RFC2205]. To ensure the integrity of RSVP, the RSVP Authentication
mechanisms defined in [RFC2747] and [RFC3097] SHOULD be supported.
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.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] discusses applicability of
various keying approaches for RSVP Authentication. First, we note
that the discussion about applicability of group keying to an intra-
provider environment where RSVP hops are not IP hops is relevant to
securing of RSVP among PEs of a given Service Provider deploying the
solution specified in the present document. We note that the RSVP
signaling in MPLS VPN is likely to spread over multiple
administrative domains (e.g. The service provider operating the VPN
service, and the customers of the service). Therefore the
considerations in [I-D.ietf-tsvwg-rsvp-security-groupkeying] about
inter-domain issues are likely to apply.
Since RSVP messages travel through the L3VPN cloud directly addressed
to PE or ASBR routers (without IP router alert option), P routers
remain isolated from RSVP messages signaling customer reservations.
Providers MAY choose to block PEs from sending datagrams with the
router alert option to P routers as a security practice, without
impacting the functionality described herein.
Beyond those general issues, four specific issues are introduced by
this document: resource usage on PEs, resource usage in the provider
backbone, PE route advertisement outside the AS, and signaling
exposure to ASBRs and PEs. We discuss these in turn.
A customer who makes resource reservations on the CE-PE links for his
sites is only competing for link resources with himself, as in
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standard RSVP, at least in the common case where each CE-PE link is
dedicated to a single customer. Thus, from the perspective of the
CE-PE links, the present document does not introduce any new security
issues. However, because a PE typically serves multiple customers,
there is also the possibility that a customer might attempt to use
excessive computational resources on a PE (CPU cycles, memory etc.)
by sending large numbers of RSVP messages to a PE. In the extreme
this could represent a form of denial-of-service attack. In order to
prevent such an attack, a PE SHOULD support mechanisms to limit the
fraction of its processing resources that can be consumed by any one
CE or by the set of CEs of a given customer. For example, a PE might
implement a form of rate limiting on RSVP messages that it receives
from each CE. We observe that these security risks and measures
related to PE resource usage are very similar for any control plane
protocol operating between CE and PE (e.g. RSVP, routing,
multicast).
The second concern arises only when the service provider chooses to
offer resource reservation across the backbone, as described in
Section 4. In this case, the concern may be that a single customer
might attempt to reserve a large fraction of backbone capacity,
perhaps with a co-ordinated effort from several different CEs, thus
denying service to other customers using the same backbone.
[RFC4804] provides some guidance on the security issues when RSVP
reservations are aggregated onto MPLS tunnels, which are applicable
to the situation described here. We note that a provider MAY use
local policy to limit the amount of resources that can be reserved by
a given customer from a particular PE, and that a policy server could
be used to control the resource usage of a given customer across
multiple PEs if desired. It is RECOMMENDED that an implementation of
this specification support local policy on the PE to control the
amount of resources that can be reserved by a given customer/CE.
Use of the VPN-IPv4 RSVP_HOP object requires exporting a PE VPN-IPv4
route to another AS, and potentially could allow unchecked access to
remote PEs if those routes were indiscriminately redistributed.
However, as described in Section 3.1, no route which is not within a
customer's VPN should ever be advertised to (or reachable from) that
customer. If a PE uses a local address already within a customer VRF
(like PE-CE link address), it MUST NOT send this address in any RSVP
messages in a different customer VRF. A "control plane" VPN MAY be
created across PEs and ASBRs and addresses in this VPN can be used to
signal RSVP sessions for any customers, but these routes MUST NOT be
advertised to, or made reachable from, any customer. An
implementation of the present document MAY support such operation
using a "control plane" VPN. Alternatively, ASBRs MAY implement the
signaling procedures described in Section 5.2.1, even if admission
control is not required on the inter-AS link, as these procedures do
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not require any direct P/PE route advertisement out of the AS.
Finally, certain operations described herein (Section 3) require an
ASBR or PE to receive and locally process a signaling packet
addressed to the BGP next-hop address advertised by that router.
This requirement does not strictly apply to MPLS/BGP VPNs [RFC4364].
This could be viewed as opening ASBRs and PEs to being directly
addressable by customer devices where they were not open before, and
could be considered a security issue. If a provider wishes to
mitigate this situation, the implementation MAY support the "control
protocol VPN" approach described above. That is, whenever a
signaling message is to be sent to a PE or ASBR, the address of the
router in question would be looked up in the "control protocol VPN",
and the message would then be sent on the LSP that is found as a
result of that lookup. This would ensure that the router address is
not reachable by customer devices.
[RFC4364] mentions use of IPsec both on a CE-CE basis and PE-PE
basis: "Cryptographic privacy is not provided by this architecture,
nor by Frame Relay or ATM VPNs. These architectures are all
compatible with the use of cryptography on a CE-CE basis, if that is
desired. The use of cryptography on a PE-PE basis is for further
study."
The procedures specified in the present document for admission
control on the PE-CE links (Section 3) are compatible with the use of
IPsec on a PE-PE basis. The optional procedures specified in the
present document for admission control in the Service Provider's
backbone (Section 4) are not compatible with the use of IPsec on a
PE-PE basis, since those procedures depend on the use of PE-PE MPLS
TE Tunnels to perform aggregate reservations through the Service
Provider's backbone.
[RFC4923] describes a model for RSVP operation through IPsec
Gateways. In a nutshell, a form of hierarchical RSVP reservation is
used where an RSVP reservation is made for the IPsec tunnel and then
individual RSVP reservations are admitted/aggregated over the tunnel
reservation. This model applies to the case where IPsec is used on a
CE-CE basis. In that situation, the procedures defined in the
present document would simply apply "as is" to the reservation
established for the IPsec tunnel(s).
11. Acknowledgments
Thanks to Ashwini Dahiya, Prashant Srinivas, Yakov Rekhter, Eric
Rosen, Dan Tappan and Lou Berger for their many contributions to
solving the problems described in this document. Thanks to Ferit
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Yegenoglu for his useful comments. We also thank Stefan Santesson
Vijay Gurbani and Alexey Melnikov for their review comments. We
thank Richard Woundy for his very thorough review and comments
including those that resulted in additional text discussing scenarios
of admission control reject in the MPLVS VPN cloud.
Appendix A. Alternatives Considered
At this stage a number of alternatives to the approach described
above have been considered. We document some of the approaches
considered here to assist future discussion. None of these has been
shown to improve upon the approach described above, and the first two
seem to have significant drawbacks relative to the approach described
above.
Appendix A.1. GMPLS UNI approach
[RFC4208] defines the GMPLS UNI. In Section 7 the operation of the
GMPLS UNI in a VPN context is briefly described. This is somewhat
similar to the problem tackled in the current document. The main
difference is that the GMPLS UNI is primarily aimed at the problem of
allowing a CE device to request the establishment of an LSP across
the network on the other side of the UNI. Hence the procedures in
[RFC4208] would lead to the establishment of an LSP across the VPN
provider's network for every RSVP request received, which is not
desired in this case.
To the extent possible, the approach described in this document is
consistent with [RFC4208], while filling in more of the details and
avoiding the problem noted above.
Appendix A.2. VRF label approach
Another approach to solving the problems described here involves the
use of label switching to ensure that Path, Resv, and other RSVP
messages are directed to the appropriate VRF. One challenge with
such an approach is that [RFC4364] does not require labels to be
allocated for VRFs, only for customer prefixes, and that there is no
simple, existing method for advertising the fact that a label is
bound to a VRF. If, for example, an ingress PE sent a Path message
labelled with a VPN label that was advertised by the egress PE for
the prefix that matches the destination address in the Path, there is
a risk that the egress PE would simply label-switch the Path directly
on to the CE without performing RSVP processing.
A second challenge with this approach is that an IP address needs to
be associated with a VRF and used as the PHOP address for the Path
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message sent from ingress PE to egress PE. That address needs to be
reachable from the egress PE, and to exist in the VRF at the ingress
PE. Such an address is not always available in today's deployments,
so this represents at least a change to existing deployment
practices.
Appendix A.3. VRF label plus VRF address approach
It is possible to create an approach based on that described in the
previous section which addresses the main challenges of that
approach. The basic approach has two parts: (a) define a new BGP
Extended Community to tag a route (and its associated MPLS label) as
pointing to a VRF; (b) allocate a "dummy" address to each VRF,
specifically to be used for routing RSVP messages. The dummy address
(which could be anything, e.g. a loopback of the associated PE) would
be used as a PHOP for Path messages and would serve as the
destination for Resv messages but would not be imported into VRFs of
any other PE.
12. References
12.1. Normative References
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997.
[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.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999.
[RFC3175] Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations",
RFC 3175, September 2001.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
"BGP-MPLS IP Virtual Private Network (VPN) Extension for
IPv6 VPN", RFC 4659, September 2006.
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[RFC4804] Le Faucheur, F., "Aggregation of Resource ReSerVation
Protocol (RSVP) Reservations over MPLS TE/DS-TE Tunnels",
RFC 4804, February 2007.
12.2. Informative References
[I-D.ietf-intarea-router-alert-considerations]
Faucheur, F., "IP Router Alert Considerations and Usage",
draft-ietf-intarea-router-alert-considerations-00 (work in
progress), March 2010.
[I-D.ietf-l3vpn-e2e-rsvp-te-reqts]
Kumaki, K., Kamite, Y., and R. Zhang, "Requirements for
supporting Customer RSVP and RSVP-TE over a BGP/MPLS IP-
VPN", draft-ietf-l3vpn-e2e-rsvp-te-reqts-05 (work in
progress), December 2009.
[I-D.ietf-mpls-ip-options]
Jaeger, W., Mullooly, J., Scholl, T., and D. Smith,
"Requirements for Label Edge Router Forwarding of IPv4
Option Packets", draft-ietf-mpls-ip-options-03 (work in
progress), January 2010.
[I-D.ietf-nsis-ntlp]
Schulzrinne, H. and M. Stiemerling, "GIST: General
Internet Signalling Transport", draft-ietf-nsis-ntlp-20
(work in progress), June 2009.
[I-D.ietf-nsis-qos-nslp]
Manner, J., Karagiannis, G., and A. McDonald, "NSLP for
Quality-of-Service Signaling", draft-ietf-nsis-qos-nslp-18
(work in progress), January 2010.
[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-05 (work in
progress), June 2009.
[RFC1633] Braden, B., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, June 1994.
[RFC2209] Braden, B. and L. Zhang, "Resource ReSerVation Protocol
(RSVP) -- Version 1 Message Processing Rules", RFC 2209,
September 1997.
[RFC2210] Wroclawski, J., "The Use of RSVP with IETF Integrated
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Services", RFC 2210, September 1997.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, January 2000.
[RFC2748] Durham, D., Boyle, J., Cohen, R., Herzog, S., Rajan, R.,
and A. Sastry, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000.
[RFC2749] Herzog, S., Boyle, J., Cohen, R., Durham, D., Rajan, R.,
and A. Sastry, "COPS usage for RSVP", RFC 2749,
January 2000.
[RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
and S. Molendini, "RSVP Refresh Overhead Reduction
Extensions", RFC 2961, April 2001.
[RFC3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value", RFC 3097,
April 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.
[RFC4860] Le Faucheur, F., Davie, B., Bose, P., Christou, C., and M.
Davenport, "Generic Aggregate Resource ReSerVation
Protocol (RSVP) Reservations", RFC 4860, May 2007.
[RFC4923] Baker, F. and P. Bose, "Quality of Service (QoS) Signaling
in a Nested Virtual Private Network", RFC 4923,
August 2007.
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Authors' Addresses
Bruce Davie
Cisco Systems, Inc.
1414 Mass. Ave.
Boxborough, MA 01719
USA
Email: bsd@cisco.com
Francois le Faucheur
Cisco Systems, Inc.
Village d'Entreprise Green Side - Batiment T3
400, Avenue de Roumanille
Biot Sophia-Antipolis 06410
France
Email: flefauch@cisco.com
Ashok Narayanan
Cisco Systems, Inc.
1414 Mass. Ave.
Boxborough, MA 01719
USA
Email: ashokn@cisco.com
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