Networking Working Group Rich Bradford (Ed)
Internet-Draft JP Vasseur
Intended Status: Standards Track Cisco Systems, Inc.
Created: November 17, 2008 Adrian Farrel
Expires: May 17, 2009 Old Dog Consulting
Preserving Topology Confidentiality in Inter-Domain Path
Computation Using a Key-Based Mechanism
draft-ietf-pce-path-key-05.txt
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Abstract
Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
Traffic Engineering (TE) Label Switched Paths (LSPs) may be
computed by Path Computation Elements (PCEs). Where the TE LSP
crosses multiple domains, such as Autonomous Systems (ASes), the
path may be computed by multiple PCEs that cooperate, with each
responsible for computing a segment of the path. However, in some
cases (e.g., when ASes are administered by separate Service
Providers), it would break confidentiality rules for a PCE to
supply a path segment to a PCE in another domain, thus disclosing
AS-internal topology information. This issue may be circumvented
by returning a loose hop and by invoking a new path computation
from the domain boundary Label Switching Router (LSR) during TE
LSP setup as the signaling message enters the second domain, but
this technique has several issues including the problem of
maintaining path diversity.
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This document defines a mechanism to hide the contents of a
segment of a path, called the Confidential Path Segment (CPS). The
CPS may be replaced by a path-key that can be conveyed in the PCE
Communication Protocol (PCEP) and signaled within in a Resource
Reservation Protocol TE (RSVP-TE) explicit route object.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC-2119 [RFC2119].
Table of contents
1. Introduction.................................................3
1.1. Terminology.................................................4
2. Path-Key Solution............................................5
2.1. Mode of Operation...........................................5
2.2. Example.....................................................6
3. PCEP Protocol Extensions.....................................7
3.1. Path Keys in PCRep Messages.................................7
3.1.1. PKS with 32-bit PCE ID....................................8
3.1.2. PKS with 128-bit PCE ID...................................9
3.2. Unlocking Path Keys.........................................9
3.2.1. Path Key Bit.............................................10
3.2.2. PATH-KEY Object..........................................10
3.2.3. Path Computation Request (PCReq) message with Path Key...10
4. PCEP Mode of Operation for Path Key Expansion...............11
5. Security Considerations.....................................12
6. Manageability Considerations................................13
6.1. Control of Function Through Configuration and Policy.......13
6.2. Information and Data Models................................14
6.3. Liveness Detection and Monitoring..........................14
6.4. Verifying Correct Operation................................14
6.5. Requirements on Other Protocols and Functional Components..15
6.6. Impact on Network Operation................................15
7. IANA Considerations.........................................15
7.1. New Subobjects for the ERO Object..........................15
7.2. New PCEP Object............................................16
7.3. New RP Object Bit Flag.....................................16
7.4. New NO-PATH-VECTOR TLV Bit Flag............................16
8. Normative References........................................17
9. Informational References....................................17
10. Acknowledgements...........................................18
11. Authors' Addresses.........................................18
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1. Introduction
Path computation techniques using the Path Computation Element
(PCE) are described in [RFC4655] and allow for path computation of
inter-domain Multiprotocol Label Switching (MPLS) Traffic
Engineering (TE) and Generalized MPLS (GMPLS) Label Switched Paths
(LSPs).
An important element of inter-domain TE is that TE information is
not shared between domains for scalability and confidentiality
reasons ([RFC4105] and [RFC4216]). Therefore, a single PCE is
unlikely to be able to compute a full inter-domain path.
Two path computation scenarios can be used for inter-domain TE
LSPs: one using per-domain path computation (defined in [RFC5152]),
and the other using a PCE-based path computation technique with
cooperation between PCEs (as described in [RFC4655]). In this second
case, paths for inter-domain LSPs can be computed by cooperation
between PCEs each of which computes a segment of the path across one
domain. Such a path computation procedure is described in [BRPC].
If confidentiality is required between domains (such as would very
likely be the case between Autonomous Systems (ASes) belonging to
different Service Providers) then cooperating PCEs cannot exchange
path segments or else the receiving PCE and the Path Computation
Client (PCC) will be able to see the individual hops through
another domain thus breaking the confidentiality requirement
stated in [RFC4105] and [RFC4216]. We define the part of the path
which we wish to keep confidential as the Confidential Path
Segment (CPS).
One mechanism for preserving the confidentiality of the CPS is for
the PCE to return a path containing a loose hop in place of the
segment that must be kept confidential. The concept of loose and
strict hops for the route of a TE LSP is described in [RFC3209].
The Path Computation Element Communication Protocol (PCEP) defined
in [PCEP] supports the use of paths with loose hops, and it is a
local policy decision at a PCE whether it returns a full explicit
path with strict hops or uses loose hops. Note that a Path
computation Request may request an explicit path with strict hops
or may allow loose hops as detailed in [PCEP].
The option of returning a loose hop in place of the CPS can be
achieved without further extensions to PCEP or the signaling
protocol. If loose hops are used, the TE LSPs are signaled as
normal ([RFC3209]), and when a loose hop is encountered in the
explicit route it is resolved by performing a secondary path
computation to reach the resource or set of resources identified
by the loose hop. Given the nature of the cooperation between PCEs
in computing the original path, this secondary computation occurs
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at or on behalf of a Label Switching Router (LSR) at a domain
boundary (i.e., an Area Border Router (ABR) or an AS Border Router
(ASBR)) and the path is expanded as described in [RFC5152].
The PCE-based computation model is particularly useful for
determining mutually disjoint inter-domain paths such as might be
required for service protection [RFC5298]. A single path computation
request is used. However, if loose hops are returned, the path of
each TE LSP must be recomputed at the domain boundaries as the TE
LSPs are signaled, and since the TE LSP signaling proceeds
independently for each TE LSP, disjoint paths cannot be guaranteed
since the LSRs in charge of expanding the EROs are not synchronized.
Therefore, if the loose hop technique is used without further
extensions, path segment confidentiality and path diversity are
mutually incompatible requirements.
This document defines the notion of a Path Key that is a token
that replaces a path segment in an explicit route. The Path Key is
encoded as a Path Key Subobject (PKS) returned in the PCEP Path
Computation Reply message (PCRep) ([PCEP]). Upon receiving the
computed path, the PKS will be carried in an RSVP-TE Path message
(RSVP-TE [RFC3209] and [RSVP-PKS]) during signaling.
The BNF in this document follows the format described in [RBNF].
1.1. Terminology
This document makes use of the following terminology and acronyms.
AS: Autonomous System.
ASBR: Autonomous System Border Routers used to connect to another
AS of a different or the same Service Provider via one or more
links inter-connecting between ASes.
CPS: Confidential Path Segment. A segment of a path that contains
nodes and links that the AS policy requires to not be disclosed
outside the AS.
Inter-AS TE LSP: A TE LSP that crosses an AS boundary.
LSR: Label Switching Router.
LSP: Label Switched Path.
PCC: Path Computation Client: Any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: An entity (component, application
or network node) that is capable of computing a network path or
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route based on a network graph and applying computational
constraints.
TE LSP: Traffic Engineering Label Switched Path
2. Path-Key Solution
The Path-Key solution may be applied in the PCE-based path
computation context as follows. A PCE computes a path segment
related to a particular domain and replaces any CPS in the path
reported to the requesting PCC (or another PCE) by one or more
subobjects referred to as PKSes. The entry boundary LSR of each
CPS SHOULD be specified using its TE Router Id as a hop in the
returned path immediately preceding the CPS, and other sub-objects
MAY be included in the path immediately before the hop identifying
the boundary LSR to indicate link and label choices. Where two
PKSes are supplied in sequence with no intervening nodes, the
entry node to the second CPS MAY be part of the first CPS and does
not need to be explicitly present in the returned path. The exit
node of a CPS MAY be present as a strict hop immediately following
the PKS.
2.1. Mode of Operation
During path computation, when local policy dictates that
confidentiality must be preserved for all or part of the path
segment being computed or if explicitly requested by the Path
Computation Request, the PCE associates a path-key with the
computed path for the CPS, places its own identifier (its PCE ID
as defined in Section 3.1) along with the path-key in a PKS, and
inserts the PKS object in the path returned to the requesting PCC
or PCE immediately after the subobject that identifies (using the
TE Router Id) the LSR that will expand the PKS into explicit path
hops.This will usually be the LSR that is the start point of the
CPS. The PCE that generates a PKS SHOULD store the computed path
segment and the path-key for later retrieval. A local policy
SHOULD be used to determine for how long to retain such stored
information, and whether to discard the information after it has
been queried using the procedures described below. It is
RECOMMENDED for a PCE to store the PKS for a period of 10 minutes.
A path-key value is scoped to the PCE that computed it as
identified by the PCE-ID carried in the PKS. A PCE MUST NOT re-use
a path-key value to represent a new CPS for at least 30 minutes
after discarding the previous use of the same path-key. A PCE that
is unable to retain information about previously used path-key
values over a restart SHOULD use some other mechanism to guarantee
uniqueness of path-key values such as embedding a timestamp or
version number in the path-key.
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A head-end LSR that is a PCC converts the path returned by a PCE
into an explicit route object (ERO) that it includes in the
Resource Reservation Protocol (RSVP) Path message. If the path
returned by the PCE contains a PKS, this is included in the ERO.
Like any other subobjects, the PKS is passed transparently from
hop to hop, until it becomes the first subobject in the ERO. This
will occur at the start of the CPS which will usually be the
domain boundary. The PKS MUST be preceded by an ERO subobject that
identifies the LSR that must expand the PKS. This means that
(following the rules for ERO processing set out in [RFC3209])
the PKS will not be encountered in ERO processing until the ERO is
being processed by the LSR that is capable of correctly handling the
PKS.
An LSR that encounters a PKS when trying to identify the next-hop
retrieves the PCE-ID from the PKS and sends a Path Computation
Request (PCReq) message as defined in [PCEP] to the PCE identified
by the PCE-ID that contains the path-key object .
Upon receiving the PCReq message, the PCE identifies the computed
path segment using the supplied path-key, and returns the
previously computed path segment in the form of explicit hops
using an ERO object contained in the Path Computation Reply
(PCReqp) to the requesting node as defined in [PCEP]. The
requesting node inserts the explicit hops into the ERO and
continues to process the TE LSP setup as per [RFC3209].
2.2. Example
Figure 1 shows a simple two-AS topology with a PCE responsible
for the path computations in each AS. An LSP is requested from
the ingress LSR in one AS to the egress LSR in the other AS. The
ingress, acting as PCC, sends a path computation request to PCE-
1. PCE-1 is unable to compute an end-to-end path and invokes PCE-
2 (possibly using the techniques described in [BRPC]). PCE-2
computes a path segment from ASBR-2 to the egress as {ASBR-2, C,
D, Egress}. It could pass this path segment back to PCE-1 in
full, or it could send back the path {ASBR-2, Egress} where the
second hop is a loose hop.
However, in order to protect the confidentiality of the topology
in the second AS while still specifying the path in full, PCE-2
may send PCE-1 a path segment expressed as {ASBR-2, PKS, Egress}
where the PKS is a Path Key Subobject as defined in this
document. In this case, PCE-2 has identified the segment {ASBR-2,
C, D, Egress} as a Confidential Path Segment (CPS). PCE-1 will
compute the path segment that it is responsible for, and will
supply the full path to the PCC as {Ingress, A, B, ASBR-1, ASBR-
2, PKS, Egress}.
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Signaling proceeds in the first AS as normal, but when the Path
message reaches ASBR-2 the next hop is the PKS, and this must be
expanded before signaling can progress further. ASBR-2 uses the
information in the PKS to request PCE-2 for a path segment, and
PCE-2 will return the segment {ASBR-2, C, D, Egress} allowing
signaling to continue to set up the LSP.
----------------------------- ----------------------------
| ------- | | ------- |
| | PCE-1 |<---------------+--+-->| PCE-2 | |
| ------- | | ------- |
| ^ | | ^ |
| | | | | |
| v | | v |
| ------- ---- | | ---- |
| | PCC | - - |ASBR| | | |ASBR| - - ------ |
| |Ingress|--|A|--|B|--| 1 |-+--+-| 2 |--|C|--|D|--|Egress| |
| ------- - - ----- | | ---- - - ------ |
| | | |
----------------------------- ----------------------------
Figure 1 : A Simple network to demonstrate the use of the PKS
3. PCEP Protocol Extensions
3.1. Path Keys in PCRep Messages
Path Keys are carried in PCReq and PCRep messages as part of the
various objects that carry path definitions. In particular, a Path
Key is carried in the Explicit Route Object (ERO) on PCRep
messages.
In all cases, the Path Key is carried in a Path Key Subobject
(PKS).
The PKS is a fixed-length subobject containing a Path-Key and a
PCE-ID. The Path Key is an identifier, or token used to represent
the CPS within the context of the PCE identified by the PCE-ID.
The PCE-ID identifies the PCE that can decode the Path Key using
an identifier that is unique within the domain that the PCE
serves. The PCE-ID has to be mapped to a reachable IPv4 or IPv6
address of the PCE by the first node of the CPS (usually a domain
border router) and a PCE MAY use one of its reachable IP addresses
as its PCE-ID. Alternatively and to provide greater security (see
Section 5) or increased confidentiality, according to domain-local
policy, the PCE MAY use some other identifier that is scoped only
within the domain.
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To allow IPv4 and IPv6 addresses to be carried, two subobjects are
defined in the following subsections.
The Path Key Subobject may be present in the PCEP ERO or the PCEP
PATH-KEY object (see Section 3.2).
3.1.1. PKS with 32-bit PCE ID
The Subobject Type for the PKS with 32-bit PCE ID is to be
assigned by IANA (recommended value 64). The format of this
subobject is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Path Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PCE ID (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
The L bit SHOULD NOT be set, so that the subobject represents a
strict hop in the explicit route.
Type
Subobject Type for a Path Key with 32-bit PCE ID as assigned by
IANA.
Length
The Length contains the total length of the subobject in bytes,
including the Type and Length fields. The Length is always 8.
PCE ID
A 32-bit identifier of the PCE that can decode this key. The
identifier MUST be unique within the scope of the domain that
the CPS crosses, and MUST be understood by the LSR that will
act as PCC for the expansion of the PKS. The interpretation of
the PCE-ID is subject to domain-local policy. It MAY be an IPv4
address of the PCE that is always reachable, and MAY be an
address that is restricted to the domain in which the LSR that
is called upon to expand the CPS lies. Other values that have
no meaning outside the domain (for example, the Router ID of
the PCE) MAY be used to increase security or confidentiality
(see Section 5).
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3.1.2. PKS with 128-bit PCE ID
The Subobject Type for the PKS with 128-bit PCE ID is to be
assigned by IANA (recommended value 65). The format of the
subobject is as follows.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Path Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PCE ID (16 bytes) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
As above.
Type
Subobject Type for a Path Key with 128-bit PCE ID as assigned
by IANA.
Length
The Length contains the total length of the subobject in bytes,
including the Type and Length fields. The Length is always 20.
PCE ID
A 128-bit identifier of the PCE that can decode this key. The
identifier MUST be unique within the scope of the domain that
the CPS crosses, and MUST be understood by the LSR that will
act as PCC for the expansion of the PKS. The interpretation of
the PCE-ID is subject to domain-local policy. It MAY be an IPv6
address of the PCE that is always reachable, but MAY be an
address that is restricted to the domain in which the LSR that
is called upon to expand the CPS lies. Other values that have
no meaning outside the domain (for example, the IPv6 TE Router
ID) MAY be used to increase security (see Section 5).
3.2. Unlocking Path Keys
When a network node needs to decode a Path Key so that it can
continue signaling for an LSP, it must send a PCReq to the
designated PCE. The PCReq defined in [PCEP] needs to be modified
to support this usage which differs from the normal path
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computation request. To that end, a new flag is defined to show
that the PCReq relates to the expansion of a PKS, and a new object
is defined to carry the PKS in the PCReq. These result in an
update to the BNF for the message. The BNF used in this document is
as described in [RBNF].
3.2.1. Path Key Bit
[PCEP] defines the Request Parameters (RP) object that is used to
specify various characteristics of the path computation request
(PCReq).
In this document we define a new bit named the Path Key bit as
follows. See Section 7.3 for the IANA assignment of the
appropriate bit number.
Path Key bit: When set, the requesting PCC requires the retrieval
of a Confidential Path Segment that corresponds to the PKS carried
in a PATH_KEY object in the path computation request. The Path Key
bit MUST be cleared when the path computation request is not
related to a CPS retrieval.
3.2.2. PATH-KEY Object
When a PCC needs to expand a path-key in order to expand a CPS it
issues a path computation request (PCReq) to the PCE identified in
the PKS in the RSVP-TE ERO that it is processing. The PCC supplies
the PKS to be expanded in a PATH-KEY Object in the PCReq message.
The PATH-KEY Object is defined as follows.
PATH-KEY Object-Class is to be assigned by IANA (recommended
value=16)
Path Key Object-Type is to be assigned by IANA (recommended
value=1)
The PATH-KEY Object MUST contain at least one Path Key Subobject
(see Section 3.1). The first PKS MUST be processed by the PCE.
Subsequent subobjects SHOULD be ignored.
3.2.3. Path Computation Request (PCReq) message with Path Key
The format of a PCReq message including a PATH-KEY object is
unchanged as follows:
<PCReq Message>::= <Common Header>
[<SVEC-list>]
<request-list>
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where:
<svec-list>::=<SVEC>[<svec-list>]
<request-list>::=<request>[<request-list>]
To support the use of the message to expand a PKS, the definition
of <request> is modified as follows :
<request>::= <RP>
<segment-computation> | <path-key-expansion>
where:
<segment-computation> ::= <END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>]
[<IRO>]
[<LOAD-BALANCING>]
<path-key-expansion> ::= <PATH-KEY>
Thus, the format of the message for use in normal path computation
is unmodified.
4. PCEP Mode of Operation for Path Key Expansion
The retrieval of the explicit path (the CPS) associated with a PKS
by a PCC is no different than any other path computation request
with the exception that the PCReq message MUST contain a PATH_KEY
object and the Path Key bit of the RP object MUST the set. On
receipt of a PCRep containing a CPS, the requesting PCC SHOULD
use insert the CPS into the ERO that it will signal, in accordance
with local policy.
If the receiving PCE does not recognize itself as identified by the
PCE ID carried in the PKS it MAY forward the PCReq message to
another PCE according to local policy. If the PCE does not forward
such a PCReq, it MUST respond with a PCRep message containing a NO-
PATH object.
If the receiving PCE recognizes itself, but cannot find the
related CPS, or if the retrieval of the CPS is not allowed by
policy, the PCE MUST send a PCRep message that contains a NO-PATH
object. The NO-PATH-VECTOR TLV SHOULD be used as described in
[PCEP] and a new bit-number (see Section 7.4) is assigned to
indicate "Cannot expand PKS".
Upon receipt of a negative reply, the requesting LSR MUST fail the
LSP setup and SHOULD use the procedures associated with loose hop
expansion failure [RFC3209].
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5. Security Considerations
This document describes tunneling confidential path information
across an untrusted domain (such as an AS). There are many
security considerations that apply to PCEP and RSVP-TE.
Issues include:
- Confidentiality of the CPS (can other network elements probe for
expansion of path-keys, possibly at random?).
- Authenticity of the path-key (resilience to alteration by
intermediaries, resilience to fake expansion of path-keys).
- Resilience from DoS attacks (insertion of spurious path-keys;
flooding of bogus path-key expansion requests).
Most of the interactions required by this extension are point to
point, can be authenticated and made secure as described in [PCEP]
and [RFC3209]. These interactions include the:
- PCC->PCE request
- PCE->PCE request(s)
- PCE->PCE response(s)
- PCE->PCC response
- LSR->LSR request and response (Note that a rogue LSR could
modify the ERO and insert or modify Path Keys. This would
result in an LSR (which is downstream in the ERO) sending
decode requests to a PCE. This is actually a larger problem
with RSVP. The rogue LSR is an existing issue with RSVP and
will not be addressed here.
- LSR->PCE request. Note that the PCE can check that the LSR
requesting the decode is the LSR at the head of the Path Key.
This largely contains the previous problem to DoS rather than
a security issue. A rogue LSR can issue random decode
requests, but these will amount only to DoS.
- PCE->LSR response.
Thus, the major security issues can be dealt with using standard
techniques for securing and authenticating point-to-point
communications. In addition, it is recommended that the PCE
providing a decode response should check that the LSR that issued
the decode request is the head end of the decoded ERO segment.
Further protection can be provided by using a PCE ID to identify
the decoding PCE that is only meaningful within the domain that
contains the LSR at the head of the CPS. This may be an IP address
that is only reachable from within the domain, or some not-address
value. The former requires configuration of policy on the PCEs,
the latter requires domain-wide policy.
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6. Manageability Considerations
6.1. Control of Function Through Configuration and Policy
The treatment of a path segment as a CPS, and its substitution in
a PCReq ERO with a PKS, is a function that MUST be under operator
and policy control where a PCE supports the function. The operator
MUST be given the ability to specify which path segments are to be
replaced and under what circumstances. For example, an operator
might set a policy that states that every path segment for the
operator's domain will be replaced by a PKS when the PCReq has
been issued from outside the domain.
The operation of the PKS extensions require that path-keys are
retained by the issuing PCE to be available for retrieval by an
LSR (acting as a PCC) at a later date. But it is possible that the
retrieval request will never be made, so good housekeeping
requires that a timer is run to discard unwanted path-keys. A
default value for this timer is suggested in Section 2.1.
Implementations SHOULD provide the ability for this value to be over-
ridden through operator configuration or policy.
After a PKS has been expanded in response to a retrieval request,
it may be valuable to retain the path-key and CPS for debug
purposes. Such retention SHOULD NOT be the default behavior of an
implementation, but MAY be available in response to operator request.
Once a path-key has been discarded, the path-key value SHOULD NOT
be immediately available for re-use for a new CPS since this might
lead to accidental misuse. A default timer value is suggested in
Section 2.1. Implementations SHOULD provide the ability for this
value to be over-ridden through operator configuration or policy.
A PCE must set a PCE-ID value in each PKS it creates so that PCCs
can correctly identify it and send PCReq messages to expand the
PKS to a path segment. A PCE implementation SHOULD allow operator
or policy control of the value to use as the PCE-ID. If the PCE
allows PCE-ID values that are not routable addresses to be used,
the PCCs MUST be configurable (by the operator or through policy)
to allow them to map from the PCE-ID to a routable address of the
PCE. Such mapping may be algorithmic, procedural (for example,
mapping a PCE-ID equal to the IGP Router ID into a routable
address), or configured through a local or remote mapping table.
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6.2. Information and Data Models
A MIB module for PCEP is already defined in [PCEP-MIB]. The
configurable items listed in Section 6.1 MUST be added as readable
objects in the module and SHOULD be added as writable objects.
A new MIB module MUST be created to allow inspection of path-keys.
For a given PCE, this MIB module MUST provide a mapping from path-
key to path segment (that is, a list of hops), and MUST supply
other information including:
- The identity of the PCC that issued the original request that
led to the creation of the path-key.
- The request ID of the original PCReq.
- Whether the path-key has been retrieved yet, and if so, by which
PCC.
- How long until the path segment associated with the path-key
will be discarded.
- How long until the path-key will be available for re-use.
6.3. Liveness Detection and Monitoring
The procedures in this document extend PCEP, but do not introduce
new interactions between network entities. Thus, no new liveness
detection or monitoring is required.
It is possible that a head-end LSR that has be given a path
including PKSs replacing specific CPSs will want to know whether
the path-keys are still valid (or have timed out). However, rather
than introduce a mechanism to poll the PCE that is responsible for
the PKS, it is considered pragmatic to simply signal the
associated LSP.
6.4. Verifying Correct Operation
The procedures in this document extend PCEP, but do not introduce
new interactions between network entities. Thus, no new tools for
verifying correct operation are required.
A PCE SHOULD maintain counters and logs of the following events
that might indicate incorrect operation (or might indicate
security issues).
- Attempts to expand an unknown path-key.
- Attempts to expand an expired path-key.
- Duplicate attempts to expand the same path-key.
- Expiry of path-key without attempt to expand it.
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6.5. Requirements on Other Protocols and Functional Components
The procedures described in this document require that the LSRs
signal PKSs as defined in [RSVP-PKS]. Note that the only changes
to LSRs are at the PCCs. Specifically, changes are only needed at
the head-end LSRs that build RSVP-TE Path messages containing
Path-Key Subobjects in their EROs, and the LSRs that discover such
subobjects as next hops and must expand them. Other LSRs in the
network, even if they are on the path of the LSP, will not be
called upon to process the PKS.
6.6. Impact on Network Operation
As well as the security and confidentiality aspects addressed by
the use of the PKS, there may be some scaling benefits associated
with the procedures described in this document. For example, a
single PKS in an explicit route may substitute for many subobjects
and can reduce the overall message size correspondingly. In some
circumstances, such as when the explicit route contains multiple
subobjects for each hop (including node IDs, TE link IDs,
component link IDs for each direction of a bidirectional LSP, and
label IDs for each direction of a bidirectional LSP) or when the
LSP is a point-to-multipoint LSP, this scaling improvement may be
very significant.
Note that a PCE will not supply a PKS unless it is knows that the
LSR that will receive the PKS through signaling will be able to
handle it. Furthermore, as noted in Section 6.5, only those LSRs
specifically called upon to expand the PKS will be required to
process the subobjects during signaling. Thus, the only backward
compatibility issues associated with the procedures introduced in
this document arise when a head-end LSR receives a PCRep with an
ERO containing a PKS and does not know how to encode this into
signaling.
Since the PCE that inserted the PKS requires to keep the CPS
confidential, the legacy head-end LSR cannot be protected. It must
either fail the LSP setup, or request a new path computation
avoiding the domain that has supplied it with unknown subobjects.
7. IANA Considerations
IANA assigns values to PCEP parameters in registries defined in
[PCEP]. IANA is requested to make the following additional
assignments.
7.1. New Subobjects for the ERO Object
IANA has previously assigned an Object-Class and Object-Type to
the ERO carried in PCEP messages [PCEP]. IANA also maintains a
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draft-ietf-pce-path-key-05.txt November 2008
list of subobject types valid for inclusion in the ERO.
IANA is requested to assign two new subobject types for inclusion
in the ERO as follows:
Subobject Type
64 Path Key with 32-bit PCE ID [This.I-D]
65 Path Key with 128-bit PCE ID [This.I-D]
7.2. New PCEP Object
IANA is requested to assign a new object class in the registry of
PCEP Objects as follows.
Object Name Object Name Reference
Class Type
16 PATH-KEY 1 Path Key [This.I-D]
Subobjects
This object may carry the following subobjects as defined
for the ERO object.
64 Path Key with 32-bit PCE ID [This.I-D]
65 Path Key with 128-bit PCE ID [This.I-D]
7.3. New RP Object Bit Flag
IANA maintains a registry of bit flags carried in the PCEP RP
object as defined in [PCEP]. IANA is requested to assign a new bit
flag as follows:
Bit Hex Name Reference
Number
15 0x000100 Path Key (P-bit) [This.I-D]
7.4. New NO-PATH-VECTOR TLV Bit Flag
IANA maintains a registry of bit flags carried in the PCEP NO-
PATH-VECTOR TLV in the PCEP NO-PATH object as defined in [PCEP].
IANA is requested to assign a new bit flag as follows:
Bits Number Name Flag Reference
1 PKS expansion failure [This.I-D]
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8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[PCEP] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E.,
Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation
Element (PCE) communication Protocol (PCEP)", draft-ietf-
pce-pcep, work in progress.
9. Informative References
[RFC3209] Awduche, Berger, Gan, Li, Srinivasan and Swallow, "RSVP-TE:
Extensions to RSVP for LSP Tunnels", RFC 3209, December
2001.
[RFC4655] Farrel, Vasseur & Ash, "A Path Computation Element (PCE)-
Based Architecture", RFC 4655, August 2006.
[RSVP-PKS] Bradford, R., Vasseur, J.P., Farrel, A., "RSVP Extensions
for Path Key Support", draft-bradford-ccamp-path-key-ero,
work in progress.
[RFC5152] Vasseur, J., et al "A Per-Domain Path Computation Method
for Establishing Inter-Domain Traffic Engineering (TE)
Label Switched Paths (LSPs)", RFC 5152, Fenruary 2008.
[BRPC] Vasseur, J., et al "A Backward Recursive PCE-based
Computation (BRPC) procedure to compute shortest inter-
domain Traffic Engineering Label Switched Path", draft-
ietf-pce-brpc, work in progress.
[RFC4105] Le Roux, J., Vasseur, JP, Boyle, J., "Requirements for
Support of Inter-Area and Inter-AS MPLS Traffic
Engineering", RFC 4105, June 2005.
[RFC4216] Zhang, R., Vasseur, JP., et. al., "MPLS Inter-AS Traffic
Engineering requirements", RFC 4216, November 2005.
[RFC5298] Takeda, T., et al, "Analysis of Inter-domain Label
Switched Path (LSP) Recovery", RFC 5298, August 2008.
[PCEP-MIB] Kiran Koushik, A., and Stephan, E., "PCE communication
protocol (PCEP) Management Information Base", draft-
kkoushik-pce-pcep-mib, work in progress.
[RBNF] Farrel, A., "Reduced Backus-Naur Form (RBNF) A Syntax Used
in Various Protocol Specifications", draft-farrel-rtg-
common-bnf, work in progress.
Bradford, Vasseur, and Farrel [Page 17]
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10. Acknowledgements
The authors would like to thank Eiji Oki, Ben Campbell, and Ross
Callon for their comments on this document.
11. Authors' Addresses
Rich Bradford (Editor)
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA - 01719
USA
EMail: rbradfor@cisco.com
J.-P Vasseur
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA - 01719
USA
EMail: jpv@cisco.com
Adrian Farrel
Old Dog Consulting
EMail: adrian@olddog.co.uk
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