One document matched: draft-ietf-tsvwg-rsvp-l3vpn-00.xml
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<rfc category="std" docName="draft-ietf-tsvwg-rsvp-l3vpn-00" ipr="full3978">
<front>
<title abbrev="RSVP for L3VPNs">Support for RSVP in Layer 3 VPNs</title>
<author fullname="Bruce Davie" initials="B." surname="Davie">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>1414 Mass. Ave.</street>
<city>Boxborough</city>
<region>MA</region>
<code>01719</code>
<country>USA</country>
</postal>
<email>bsd@cisco.com</email>
</address>
</author>
<author fullname="Francois le Faucheur" initials="F."
surname="le Faucheur">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Village d'Entreprise Green Side - Batiment T3</street>
<street>400, Avenue de Roumanille</street>
<code>06410</code>
<region>Biot Sophia-Antipolis</region>
<country>France</country>
</postal>
<email>flefauch@cisco.com</email>
</address>
</author>
<author fullname="Ashok Narayanan" initials="A." surname="Narayanan">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>1414 Mass. Ave.</street>
<city>Boxborough</city>
<region>MA</region>
<code>01719</code>
<country>USA</country>
</postal>
<email>ashokn@cisco.com</email>
</address>
</author>
<date day="3" month="July" year="2008" />
<abstract>
<t>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 CE and 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.</t>
</abstract>
<note title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
<note title="Change history">
<t>[<spanx style="emph">Note to RFC Editor: This section to be removed
before publication</spanx>]</t>
<t>Changes in this version (draft-ietf-tsvwg-rsvp-l3vpn-00) relative to
the last (draft-davie-tsvwg-rsvp-l3vpn-02):</t>
<t><list style="symbols">
<t>Outlined signalling security issues and added discussion of
methods to control redistribution of routes among providers and from
providers to customers</t>
<t>Clarification regarding support for RSVP-TE across L3VPN</t>
<t>Minor corrections</t>
</list></t>
</note>
</front>
<middle>
<section title="Introduction">
<t><xref target="RFC4364" /> and <xref target="RFC4659" /> define a
Layer 3 VPN service known as BGP/MPLS VPNs for IPv4 and for IPv6
respectively. <xref target="RFC2205" /> defines the Resource Reservation
Protocol (RSVP) which may be used to perform admission control as part
of the Integrated Services (int-serv) architecture <xref
target="RFC1633" /><xref target="RFC2210" />.</t>
<t>Customers of a layer 3 VPN service may run RSVP for the purposes of
admission control 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:<list style="symbols">
<t>RSVP Path message processing depends on routers recognizing the
router alert option in the IP header. However, packets traversing
the backbone of a BGP/MPLS VPN are MPLS encapsulated and thus the
router alert option is not normally visible to the egress PE.</t>
<t>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.</t>
<t>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.</t>
</list>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 NSIS <xref
target="RFC4080" />.</t>
<t>Additionally, it may be desirable to perform admission control over
the provider's backbone on behalf of one or more L3VPN customers. 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) must also be addressed. This draft also
specifies procedures for supporting such a scenario.</t>
<t>This draft 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.</t>
<section title="Terminology">
<t>This document draws freely on the terminology defined in <xref
target="RFC2205" /> and <xref target="RFC4364" />. For convenience, we
provide a few brief definitions here:<list style="symbols">
<t>CE (Customer Edge) Router: Router at the edge of a customer
site that attaches to the network of the VPN provider.</t>
<t>PE (Provider Edge) Router: Router at the edge of the service
provider's network that attaches to one or more customer
sites.</t>
<t>VPN Label: An MPLS label associated with a route to a customer
prefix in a VPN (also called a VPN route label).</t>
<t>VRF: VPN Routing and Forwarding Table. A PE typically has
multiple VRFs, enabling it to be connected to CEs that are in
different VPNs.</t>
</list></t>
</section>
</section>
<section title="Problem Statement">
<t>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.</t>
<t>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 must be able 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. Much of this
draft deals with this issue.</t>
<t>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 <xref
target="RFC3175" /> and <xref target="RFC4804" />, with the additional
complications of handling customer-specific addressing associated with
BGP/MPLS VPNs.</t>
<t>Finally, we note that RSVP Path messages are normally addressed to
the destination of a session, and contain the router alert IP option.
Routers along the path to the destination that are configured to process
RSVP messages must detect the presence of the router alert option 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 may forward 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. This problem of recognizing and
processing Path messages is also discussed below.</t>
<section anchor="model" title="Model of Operation">
<t>Figure 1 illustrates the basic model of operation with which this
document is concerned.</t>
<figure>
<preamble />
<artwork><![CDATA[
--------------------------
/ Provider \
|----| | Backbone | |----|
Sender->| CE1| |-----| |-----| |CE2 |->Receiver
| |--| | |---| |---| | |---| |
|----| | | | P | | P | | | |----|
| PE1 |---| |-----| |-----| PE2 |
| | | | | | | |
| | |---| |---| | |
|-----| |-----|
| |
\ /
--------------------------
]]></artwork>
<postamble>Figure 1. Model of Operation for RSVP-based admission
control over MPLS/BGP VPN</postamble>
</figure>
<t />
<t>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 must take
place:<list style="numbers">
<t>Sender sends a Path message to an IP address of the
Receiver.</t>
<t>Path message is processed by CE1 using normal RSVP procedures
and forwarded towards the Receiver along the link CE1-PE1.</t>
<t>PE1 processes Path message and forwards towards the Receiver
across the provider backbone.</t>
<t>PE2 processes Path message and forwards towards the Receiver
along link PE2-CE2.</t>
<t>CE2 processes Path message using normal RSVP procedures and
forwards towards Receiver.</t>
<t>Receiver sends Resv message to CE2.</t>
<t>CE2 sends Resv message to PE2.</t>
<t>PE2 processes Resv message (including performing admission
control on link PE2-CE2) and sends Resv to PE1.</t>
<t>PE1 processes Resv message and sends Resv to CE1.</t>
<t>CE1 processes Resv using normal RSVP procedures, performs
admission control on the link CE1-PE1 and sends Resv message to
Sender if successful.</t>
</list> 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.</t>
</section>
</section>
<section anchor="cac-pe-ce" title="Admission Control on PE-CE Links">
<t>In the following sections we trace through the steps outlined in
<xref target="model" /> 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.</t>
<t>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 <xref target="objects" />.</t>
<section anchor="path-proc-i"
title="Path Message Processing at Ingress PE">
<t>When a Path message arrives at the ingress PE (step 3 of <xref
target="model" />) 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.</t>
<t>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 <xref target="RFC2205" />. The ingress PE
must recognize the router alert, intercept these messages and process
them as RSVP signalling messages.</t>
<t>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; 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 <xref target="path-proc-e" />. 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 <xref target="RFC4206" /> and <xref
target="RFC4804" />.</t>
<t>For an RSVP Path message, the existing SESSION and SENDER_TEMPLATE
objects can no longer uniquely identify a flow on VPN PE nodes. We
propose a new format of SESSION and SENDER_TEMPLATE objects which
contain a VPN-IPv4 format address. 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.</t>
<t>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 with the new VPN-IPv4 type
objects. The RSVP_HOP object in the Path message contains an IP
address of the ingress PE. The Path message is sent without IP Router
Alert.</t>
</section>
<section anchor="path-proc-e"
title="Path Message Processing at Egress PE">
<t>When a Path message arrives at the egress PE, 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.</t>
<t>Now the RSVP module can construct a Path message which differs from
the Path it received in the following ways:<list style="letters">
<t>Its destination address is the IP address extracted from the
SESSION Object;</t>
<t>The SESSION and SENDER_TEMPLATE objects are converted back to
IPv4-type by discarding the attached RD</t>
<t>The RSVP_HOP Object contains the IP address of the outgoing
interface of the egress PE and an LIH, as per normal RSVP
processing.</t>
</list>The router then sends the Path message on towards its
destination over the interface identified above. This Path message
carries the IP Router-Alert option as required by <xref
target="RFC2205" />.</t>
</section>
<section anchor="resv-proc-e" title="Resv Processing at Egress PE">
<t>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 (it is
"egress" 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.</t>
<t>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
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 contains
an IP address of the Egress PE that is reachable by the ingress PE.
The Resv message is sent to the IP address contained within the
RSVP_HOP object in the Path message.</t>
<t>If admission control is not successful on the egress PE, a
ResvError message is sent towards the receiver as per normal RSVP
processing.</t>
</section>
<section anchor="resv-proc-i" title="Resv Processing at Ingress PE">
<t>Upon receiving a Resv message at the ingress PE (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.</t>
</section>
<section title="Other RSVP Messages">
<t>Processing of PathError, PathTear, ResvError, ResvTear and ResvConf
messages is generally straightforward and follows the rules of <xref
target="RFC2205" />. These additional rules must be observed for
messages transmitted within the VPN (i.e. between the PEs):<list
style="symbols">
<t>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.</t>
<t>The matching state & VRF must be determined by decoding the
RD and IPv4 addresses in the SESSION and FILTER_SPEC objects.</t>
<t>The message must be directly addressed to the appropriate PE,
without using the IP Router Alert option.</t>
</list></t>
</section>
</section>
<section anchor="backbone"
title="Admission Control in Provider's Backbone">
<t>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.</t>
<t>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.</t>
<t>Given these considerations, a feasible way to achieve the objective
of admission control in the backbone is to use the ideas described in
<xref target="RFC4804" />. MPLS-TE tunnels can be established between
PEs as a means to perform aggregate admission control in the
backbone.</t>
<t>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 <xref
target="RFC4804" /> uses the IF_ID RSVP_HOP object to identify the
tunnel across the backbone, rather than the simple RSVP_HOP object
described in <xref target="path-proc-i" />. The procedures of <xref
target="RFC4804" /> should be followed here as well.</t>
<t>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 routing and admission control decisions.
This is all consistent with the principles of aggregate RSVP
reservations described in <xref target="RFC3175" />.</t>
</section>
<section anchor="inter-as" title="Inter-AS operation">
<t><xref target="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.</t>
<section anchor="inter-as-a" title="Inter-AS Option A">
<t>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 <xref target="cac-pe-ce" /> are enabled on both ASBRs, then CAC may
be performed on the inter-ASBR links. In addition, the operator of
each AS can independently decide whether or not to perform CAC across
his backbone. The new objects described in this document MUST NOT be
sent in any RSVP message between two Option-A ASBRs.</t>
</section>
<section anchor="inter-as-b" title="Inter-AS Option B">
<t>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.</t>
<t>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.</t>
<section anchor="inter-as-b-cac" title="Admission control on ASBR">
<t>In this scenario, the ASBR performs full RSVP signalling and
admission control. The RSVP database is indexed on the ASBR using
the VPN-IPv4 SESSION, SENDER_TEMPLATE and FILTER_SPEC objects (which
uniquely identify RSVP sessions and flows as per the requirements of
<xref target="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 <xref target="RFC2209" />,
no customer VRF awareness is required on the ASBR.</t>
</section>
<section anchor="inter-as-b-no-cac"
title="No admission control on ASBR">
<t>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. Not however that such
routers in an Option B environment are not required to have direct
IP reachability to each other. To mitigate this issue, we propose
the use of label switching to forward RSVP messages from a PE in one
AS to a PE in another AS. A detailed description of how this is
achieved follows.</t>
<t>We first define a new VPN-IPv4 RSVP_HOP object. Use of the
VPN-IPv4 RSVP_HOP object enables RSVP control plane reachability
between any two adjacent RSVP hops in a MPLS VPN, regardless of
whether they have IP reachability. RSVP nodes sending Path or Resv
messages across a MPLS VPN MAY use the VPN-IPv4 PHOP object to
achieve signalling across Option-B ASBRs without requiring the ASBRs
to install state. The requirements ("SHOULD", "MUST" etc.) specified
in the remainder of this section only apply when the implementation
supports the OPTIONAL use of the VPN-IPv4 HOP object.</t>
<t>The VPN-IPv4 RSVP_HOP object carries the IPv4 address of the
message sender and a logical interface handle 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
HOP address into BGP with an associated label, and this
advertisement MUST be propagated by BGP throughout the VPN and to
adjacent ASes in order 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. This VPN-IPv4 address MAY be created
specially for this task, or MAY be any previously-advertised address
representing any VRF (e.g. local PE-CE link address). In the case
where the address is specially created for control protocols, the
BGP advertisement for this address SHOULD be marked such that it is
not redistributed outside the MPLS VPN. Two possible methods to
achieve this goal are:</t>
<t>
<list style="symbols">
<t>Tag the advertisement of such routes with a route target that
is not imported into any customer VRFs. This requires the
creation of a special "control protocols" VPN which is used only
for these addresses.</t>
<t>Tag the advertisement with a specially defined
extended-community attribute, the meaning of which is that this
route is not to be redistributed to customers. Definition of
this attribute is beyond the scope of this document.</t>
</list>
</t>
<t>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 <xref target="path-proc-i" />, 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 CAC). This router receives the Path and
processes it as described in <xref target="path-proc-e" /> if it is
a PE, or <xref target="inter-as-b-cac" /> if it is an ASBR
performing CAC. When this router sends the Resv upstream, it queries
BGP for a next-hop and 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 (the hop that last updated the RSVP_HOP field in
the Path message), without any involvement of intermediate ASBRs.
Further, the router sending this Resv message MUST include in its
RSVP_HOP object a VPN-IPv4 address advertised by itself into BGP
with a label, so that hop-by-hop RSVP messages in the downstream
direction (e.g. ResvError) can be sent directly to it. Note that the
VPN-IPv4 address is only used to identify a LSP for neighbor
reachability. The IPv4 address in the RSVP_HOP object is used for
all other purposes, including neighbor matching between Path/Resv
and SRefresh messages (<xref target="RFC2961" />), authentication
(<xref target="RFC2747" />), etc.</t>
<t>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
signalling flow, may do so by writing its own RSVP_HOP object with
IPv4 and VPN-IPv4 address pointing to itself.</t>
<t>If an Option-B ASBR receives a RSVP Path message with an IPv4
type PHOP, does not wish to perform admission control but is willing
to install local state for this flow, the ASBR MUST process and
forward RSVP signalling messages for this flow as described in
section 5.2.1 (except admission control). If an Option-B ASBR
receives a RSVP Path message with an IPv4 type PHOP, 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 [<spanx
style="emph">TBD</spanx>], Error Value [<spanx
style="emph">TBD</spanx>], signifying to the upstream RSVP hop that
the supplied PHOP object is insufficient to provide reachability
across this VPN. The upstream node, on receipt of this PathError,
SHOULD re-send the Path message including a RSVP_HOP of VPN-IPv4
type.</t>
</section>
</section>
<section anchor="inter-as-c" title="Inter-AS Option C">
<t>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 <xref
target="cac-pe-ce" />. 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 <xref
target="backbone" />.</t>
<t />
</section>
</section>
<section title="Operation with RSVP disabled">
<t>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.</t>
</section>
<section anchor="other" title="Other RSVP procedures">
<t>This section describes modifications to other RSVP procedures
introduced by MPLS VPNs</t>
<section anchor="refresh-reduction" title="Refresh overhead reduction">
<t>The following points should be noted regarding RSVP refresh
overhead reduction (<xref target="RFC2961" />) across a MPLS VPN:</t>
<t>
<list style="symbols">
<t>The hop between the ingress and egress PE of a VPN should be
considered as traversing one or more non-RSVP hops. As such, the
procedures described in Section 5.3 of <xref target="RFC2961" />
relating to non-RSVP hops SHOULD be followed.</t>
<t>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.</t>
</list>
</t>
</section>
<section anchor="authentication" title="Cryptographic Authentication">
<t>The following points should be noted regarding RSVP cryptographic
authentication (<xref target="RFC2747" />) across a MPLS VPN:</t>
<t>
<list style="symbols">
<t>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.</t>
<t>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.</t>
</list>
</t>
</section>
<section anchor="aggregation" title="RSVP Aggregation">
<t><xref target="RFC3175" /> and <xref target="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 should be noted in this
regard:</t>
<t>
<list style="symbols">
<t>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.</t>
<t>Aggregate RSVP sessions will be treated in the same way as
regular IPv4 RSVP sessions. To this end, all the procedures
described in <xref target="cac-pe-ce" /> and <xref
target="backbone" /> apply to aggregate RSVP sessions. New
SESSION, SENDER_TEMPLATE and FILTERSPEC objects are defined in
<xref target="objects" />.</t>
<t>End-To-End (E2E) RSVP sessions are passed unmodified through
the MPLS VPN. These RSVP messages may 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 IP Router-Alert
flags. 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.</t>
<t>Any SESSION-OF-INTEREST objects (defined in <xref
target="RFC4860" />) are to be conveyed unmodified across the MPLS
VPN.</t>
</list>
</t>
</section>
<section anchor="ce-ce-lsp" title="Support for CE-CE RSVP-TE">
<t><xref target="I-D.kumaki-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
draft 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 <xref
target="I-D.kumaki-l3vpn-e2e-rsvp-te-reqts" />. To the extent that
this draft uses signalling extensions described in <xref
target="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.</t>
<t anchor="signalling-security" hangText="Signalling Security Issues" />
</section>
</section>
<section anchor="objects" title="Object Definitions">
<section anchor="obj-session"
title="VPN-IPv4 and VPN-IPv6 SESSION objects">
<t>The usage of the VPN-IPv4 SESSION Object is described in <xref
target="path-proc-i" /> and <xref target="path-proc-e" />. The
VPN-IPv4 SESSION object should appear in all 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). The VPN-IPv4 address in this object
is built by combining the IPv4 address from the incoming SESSION with
the RD in the BGP advertisement from the egress PE for this prefix and
customer.</t>
<t>The VPN-IPv6 SESSION object is analogous to the VPN-IPv4 SESSION
object, using VPN-IPv6 addresses<xref target="RFC4659" />.</t>
<t>The formats of the objects are as follows:</t>
<figure>
<preamble />
<artwork><![CDATA[
o VPN-IPv4 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 DestAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<figure>
<preamble />
<artwork><![CDATA[
o VPN-IPv6 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 DestAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<t>The protocol ID, flags, and DstPort are identical to the IPv4 and
IPv6 SESSION objects.</t>
</section>
<section anchor="obj-template"
title="VPN-IPv4 and VPN-IPv6 SENDER_TEMPLATE objects">
<t>The usage of the VPN-IPv4 SENDER_TEMPLATE Object is described in
<xref target="path-proc-i" /> and <xref target="path-proc-e" />. The
VPN-IPv4 SENDER_TEMPLATE object should appear in all 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 VPN-IPv4 address in this object is built by
combining the IPv4 address from the incoming SENDER_TEMPLATE with the
RD in the BGP advertisement from the ingress PE for this prefix and
customer. The format of the object is as follows:</t>
<figure>
<preamble />
<artwork><![CDATA[
o VPN-IPv4 SENDER_TEMPLATE object: Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 SrcAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| Reserved | SrcPort |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<figure>
<preamble />
<artwork><![CDATA[
o VPN-IPv6 SENDER_TEMPLATE object: Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 SrcAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Reserved | SrcPort |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<t>The SrcPort is identical to the IPv4 and IPv6 SENDER_TEMPLATE
objects. The Reserved field must be set to zero on transmit and
ignored on receipt.</t>
</section>
<section anchor="obj-filterspec"
title="VPN-IPv4 and VPN-IPv6 FILTER_SPEC objects">
<t>The usage of the VPN-IPv4 FILTER_SPEC Object is described in <xref
target="resv-proc-e" /> and <xref target="resv-proc-i" />. The
VPN-IPv4 FILTER_SPEC object should appear in all 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). The VPN-IPv4 address in this object is built by
combining the IPv4 address from the incoming FILTER_SPEC with the RD
in the BGP advertisement from the ingress PE for this prefix and
customer.</t>
<figure>
<preamble />
<artwork><![CDATA[
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.
]]></artwork>
<postamble />
</figure>
<t>The protocol ID, flags, and DstPort are identical to the IPv4 and
IPv6 SESSION objects.</t>
</section>
<section anchor="obj-hop" title="VPN-IPv4 and VPN-IPv6 RSVP_HOP objects">
<t>Usage of the VPN-IPv4 RSVP_HOP Object is described in <xref
target="inter-as-b-no-cac" />. The VPN-IPv4 RSVP_HOP object is used to
establish signalling reachability between RSVP neighbors separated by
one or more Option-B ASBRs. This object may appear in all 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 as follows:</t>
<figure>
<preamble />
<artwork><![CDATA[
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 |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<figure>
<preamble />
<artwork><![CDATA[
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 |
+-------------+-------------+-------------+-------------+
]]></artwork>
</figure>
</section>
<section anchor="obj-agg-session"
title="Aggregated VPN-IPv4 and VPN-IPv6 SESSION objects">
<t>The usage of Aggregated VPN-IPv4 SESSION object is described in
<xref target="aggregation" />. The AGGREGATE-VPN-IPv4 SESSION object
should appear in all RSVP messages that ordinarily contain a
AGGREGATE-IPv4 SESSION object as defined in <xref target="RFC3175" />
and are sent between ingress PE and egress PE in either direction. The
GENERIC-AGGREGATE-VPN-IPv4 SESSION object should appear in all RSVP
messages that ordinarily contain a GENERIC-AGGREGATE-IPv4 SESSION
object as defined in <xref target="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 SESSION object defined in <xref target="obj-session" />. The
VPN-IPv4 address in this object is built by combining the IPv4 address
from the incoming SESSION with the RD in the BGP advertisement from
the egress PE for this prefix and customer. The format of the object
is as follows:</t>
<figure>
<preamble />
<artwork><![CDATA[
o AGGREGATE-VPN-IPv4 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 DestAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
| /////// | Flags | /////// | DSCP |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<figure>
<preamble />
<artwork><![CDATA[
o AGGREGATE-VPN-IPv6 SESSION object: Class = 1, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 DestAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
| Reserved | Flags | Reserved | DSCP |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<t>The flags and DSCP are identical to the AGGREGATE-IPv4 and
AGGREGATE-IPv6 SESSION objects.</t>
<figure>
<preamble />
<artwork><![CDATA[
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 |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<figure>
<preamble />
<artwork><![CDATA[
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 |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<t>The flags, PHB-ID, vDstPort and Extended vDstPort are identical to
the GENERIC-AGGREGATE-IPv4 and GENERIC-AGGREGATE-IPv6 SESSION
objects.</t>
</section>
<section anchor="obj-agg-template"
title="AGGREGATE-VPN-IPv4 and AGGREGATE-VPN-IPv6 SENDER_TEMPLATE objects">
<t>The usage of Aggregated VPN-IPv4 SENDER_TEMPLATE object is
described in <xref target="aggregation" />. The AGGREGATE-VPN-IPv4
SENDER_TEMPLATE object should appear in all RSVP messages that
ordinarily contain a AGGREGATE-IPv4 SENDER_TEMPLATE object as defined
in <xref target="RFC3175" /> and <xref target="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 SENDER_TEMPLATE object defined in <xref
target="obj-template" />. The VPN-IPv4 address in this object is built
by combining the IPv4 address from the incoming SENDER_TEMPLATE with
the RD in the BGP advertisement from the ingress PE for this prefix
and customer. The format of the object is as follows:</t>
<figure>
<preamble />
<artwork><![CDATA[
o AGGREGATE-VPN-IPv4 SENDER_TEMPLATE object:
Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| VPN-IPv4 AggregatorAddress (12 bytes) |
+ +
| |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<figure>
<preamble />
<artwork><![CDATA[
o AGGREGATE-VPN-IPv6 SENDER_TEMPLATE object:
Class = 11, C-Type = TBA
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ VPN-IPv6 AggregatorAddress (24 bytes) +
/ /
. .
/ /
| |
+-------------+-------------+-------------+-------------+
]]></artwork>
<postamble />
</figure>
<t>The flags and DSCP are identical to the AGGREGATE-IPv4 and
AGGREGATE-IPv6 SESSION objects.</t>
</section>
<section anchor="obj-agg-filterspec"
title="AGGREGATE-VPN-IPv4 and AGGREGATE-VPN-IPv6 FILTER_SPEC objects">
<t>The usage of Aggregated VPN-IPv4 FILTER_SPEC object is described in
<xref target="aggregation" />. The AGGREGATE-VPN-IPv4 FILTER_SPEC
object should appear in all RSVP messages that ordinarily contain a
AGGREGATE-IPv4 FILTER_SPEC object as defined in <xref
target="RFC3175" /> and <xref target="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 FILTER_SPEC object defined in <xref
target="obj-filterspec" />. The VPN-IPv4 address in this object is
built by combining the IPv4 address from the incoming FILTER_SPEC with
the RD in the BGP advertisement from the ingress PE for this prefix
and customer. The format of the object is as follows:</t>
<figure>
<preamble />
<artwork><![CDATA[
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.
]]></artwork>
<postamble />
</figure>
<t />
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document requires IANA assignment of new RSVP C-Types to
accommodate the new objects described in <xref target="objects" />. In
addition, a new PathError code/value is required to identify a
signalling reachability failure and the need for a VPN-IPv4 or VPN-IPv6
RSVP_HOP object as described in <xref target="inter-as-b-no-cac" />.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t><xref target="RFC4364" /> addresses the security considerations of
BGP/MPLS VPNs in general. General RSVP security considerations are
addressed in <xref target="RFC2205" />. To ensure the integrity of RSVP,
the RSVP Authentication mechanisms defined in <xref target="RFC2747" />
and <xref target="RFC3097" />may be used. These 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. <xref
target="I-D.behringer-tsvwg-rsvp-security-groupkeying" /> discusses
applicability of various keying approaches for RSVP Authentication. 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 <xref
target="I-D.behringer-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), P routers remain isolated from RSVP messages
signalling customer reservations. Providers MAY choose to block PEs from
sending IP Router-Alert datagrams to P routers as a security practice,
without impacting the functionality described herein.</t>
<t>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 signalling exposure
to ASBRs and PEs. We discuss these in turn.</t>
<t>A customer who makes resource reservations on the CE-PE links for his
sites is only competing for link resources with himself, as in 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, this
draft 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 have 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)</t>
<t>The second concern arises only when the service provider chooses to
offer resource reservation across the backbone, as described in <xref
target="backbone" />. 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. <xref
target="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.</t>
<t>A third issue may arise when Inter-AS Option B is used and admission
control is not required on the inter-AS link (<xref
target="inter-as-b-no-cac" />). In this case, the VPN PE includes a
VPN-IPv4 address in the PHOP/NHOP objects it generates, which is used by
the peer to determine a VPN label to communicate back with this PE. This
results in a direct VPN-IPv4 route to a PE being exported to another AS,
and potentially could allow customers to direct RSVP messages to remote
PEs if those routes were advertised to the customers. However, as
described in <xref target="inter-as-b-no-cac" />, a variety of
techniques may be used to prevent such routes from being advertised to
customers. Alternatively, ASBRs may implement the signalling procedures
described in <xref target="inter-as-b-cac" />, even if admission control
is not required on the inter-AS link, as these procedures do not require
any direct P/PE route advertisement out of the AS.</t>
<t>Finally, certain operations described herein (<xref
target="cac-pe-ce" />) require an ASBR or PE to receive and locally
process a signalling packet addressed to the BGP next-hop address
advertised by that router. This requirement does not strictly apply to
MPLS/BGP VPNs <xref target="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, it would be possible to
use one of the approaches described in <xref
target="inter-as-b-no-cac" /> to prevent such routers from being
reachable by customers. That is, whenever a signalling 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
allow the provider to restrict advertisement of PE and ASBR addresses so
that these addresses are not reachable by customer devices.</t>
</section>
<section anchor="Acknowledgments" title="Acknowledgments">
<t>Thanks to Ashwini Dahiya, Prashant Srinivas, Yakov Rekhter, Eric
Rosen for their many contributions to solving the problems described in
this draft. Thanks to Ferit Yegenoglu and Dan Tappan for their useful
comments.</t>
</section>
<appendix anchor="altern" title="Alternatives Considered">
<t>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.</t>
<appendix title="GMPLS UNI approach">
<t><xref target="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 <xref target="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.</t>
<t>To the extent possible, the approach described in this document is
consistent with <xref target="RFC4208" />, while filling in more of
the details and avoiding the problem noted above.</t>
</appendix>
<appendix title="VRF label approach">
<t>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 <xref target="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.</t>
<t>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
message sent from ingress PE to egress PE. That address must be
reachable from the egress PE, and 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.</t>
</appendix>
<appendix title="VRF label plus VRF address approach">
<t>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.</t>
<t />
</appendix>
</appendix>
</middle>
<back>
<references title="Normative References">
<?rfc include='reference.RFC.2119'?>
<?rfc include='reference.RFC.2205'?>
<?rfc include='reference.RFC.4364'?>
<?rfc include='reference.RFC.3175'?>
<?rfc include='reference.RFC.4804'?>
<?rfc include='reference.RFC.4659'?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.1633'?>
<?rfc include='reference.RFC.2209'?>
<?rfc include='reference.RFC.2210'?>
<?rfc include='reference.RFC.3473'?>
<?rfc include='reference.RFC.4860'?>
<?rfc include='reference.RFC.3032'?>
<?rfc include='reference.RFC.4080'?>
<?rfc include='reference.RFC.2747'?>
<?rfc include='reference.RFC.2961'?>
<?rfc include='reference.RFC.3097'?>
<?rfc include='reference.RFC.4206'?>
<?rfc include='reference.RFC.4208'?>
<?rfc include='reference.I-D.kumaki-l3vpn-e2e-rsvp-te-reqts'?>
<?rfc include='reference.I-D.behringer-tsvwg-rsvp-security-groupkeying'?>
</references>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-23 01:10:56 |