Networking Working Group Rich Bradford (Ed)
Internet-Draft JP Vasseur
Cisco Systems, Inc.
Adrian Farrel
Old Dog Consulting
Proposed Status: Standard
Expires: November 1, 2007
May 1, 2007
draft-ietf-pce-path-key-00.txt
Preserving Topology Confidentiality in Inter-Domain Path
Computation using a key based mechanism
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Bradford, Vasseur and Farrel 1
Draft-ietf-pce-path-key-00.txt May 2007
Copyright Notice
Copyright (C) The IETF Trust (2007). All rights reserved.
Abstract
Multiprotocol Label Switching (MPLS) 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 (ASs), 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 ASs 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 internal topology information.
This issue may be circumvented by returning a loose hop and by
invoking a new path computation from the domain boundary LSR
during TE LSP setup as the LSP enters the second domain, but this
technique has several issues including the problem of maintaining
path diversity.
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 (RSVP) explicit route object.
Table of contents
1. Terminology..................................................3
2. Introduction.................................................3
3. Path-Key Solution............................................5
3.1. Mode of Operation...........................................5
4. PCEP Protocol Extensions.....................................6
4.1. PKS sub-object..............................................6
4.2. PKS bit.....................................................8
5. PCEP Mode of operation.......................................9
6. Security Considerations......................................9
7. Manageability Considerations................................10
8. IANA considerations.........................................10
9. Intellectual Property Considerations........................11
10. References.................................................11
10.1. Normative References.....................................11
10.2. Informational References.................................12
11. Authors' Addresses:........................................12
Bradford, Vasseur, and Farrel 2
Draft-ietf-pce-path-key-00.txt May 2007
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].
1. Terminology
ASBR: border routers used to connect to another AS of a different
or the same Service Provider via one or more links inter-
connecting between ASs.
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
route based on a network graph and applying computational
constraints.
TE LSP: Traffic Engineering Label Switched Path
2. Introduction
Path computation techniques using the Path Computation Element
(PCE) have been described in [PCE-ARCH] and allow for path
computation of inter-domain Multiprotocol Label Switching (MPLS)
traffic engineering (TE) Label Switched Paths (LSPs).
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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 [PD-PATH-
COMP]), and the other using a PCE-based path computation technique
with cooperation between PCEs (as described in [PCE-ARCH]). 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 ASs 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 non
conforming to 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 for the segment
internal to a domain that must be kept confidential. The concept
of loose 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 or uses loose hops. Note that a Path computation Request may
request a loose or explicit path as detailed in [PCEP].
One option may consist of returning loose hop without further
extensions: 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 next loose hop. Given the nature of the
cooperation between PCEs in computing the original path, this
secondary computation occurs at a Label Switching Router (LSR) at
a domain boundary (i.e. an ABR or ASBR) and the path is expanded
as described in [PD-PATH-COMP].
The PCE-based computation model is particularly useful for
determining mutually disjoint inter-domain paths such as might be
required for service protection. A single path computation request
is used. However, if loose hops are returned, the path of each TE
Bradford, Vasseur, and Farrel 4
Draft-ietf-pce-path-key-00.txt May 2007
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, using the loose hop technique 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 Sub-object (PKS) returned in the PCEP Path
Computation Reply message (PCReq) ([PCEP]). Upon receiving the
computed path, the PKS sub-object will be carried out in an RSVP-
TE Path message (RSVP-TE [RFC3209]) during signaling. The PKS may
also, optionally, be used in recorded routes in RSVP-TE.
3. 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 it in the path
reported to the requesting PCC (or another PCE) by one or more
sub-objects referred to as the PKS. The entry and boundary LSR of
each CPS SHOULD be specified as hops in the returned path
immediately preceding the PKS, but where two PKSs are supplied in
sequence the entry node to the second MAY be encoded within the
first. The exit node of a CPS MAY be present as a strict hop
immediately following the PKS, but MAY also be hidden as part of
the PKS.
3.1. 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 [PCE-MONITORING]) 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 IPv4 sub-object defined in
[RFC3209] sub-object that identifies the LSR that will expand the
PKS into a explicit path hops. This will usually be the LSR that
is the start point of the CPS. The PCE that generates a PKS MUST
Bradford, Vasseur, and Farrel 5
Draft-ietf-pce-path-key-00.txt May 2007
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 strore the PKS for
a period of 10 minutes.
TBD: Need to define the scope of the PKS and spell out the
restrictions on Path Key re-use.
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 PKSs these are included in the ERO.
Like any other sub-objects, the PKS is passed transparently from
hop to hop, until it becomes the first sub-object 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 sub-object
that identifies the LSR that must expand the PKS, so the PKS will
not be encountered in ERO processing until the LSR that can
process it.
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) as define in [PCEP] to the requesting node. The
requesting node inserts the explicit hops into the ERO and
continues to process the TE LSP setup as per [RFC3209].
4. PCEP Protocol Extensions
4.1. PKS sub-object
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Draft-ietf-pce-path-key-00.txt May 2007
The PKS object format is identical as in [RSVP-PKS] but redefined
in the context of this document since a PCEP codepoint is
required.
The PKS is a fixed-length sub-object 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 a
reachable IPv4 or IPv6 address of the PCE.
Because of the IPv4 and IPv6 variants, two sub-objects are defined
as follows.
PKS IPv4 sub-object
PKS Object-Class is to be assigned by IANA (recommended value=16)
PKS Object-Type is to be assigned by IANA (recommended value=1)
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
The L bit SHOULD NOT be set, so that the sub-object
represents a strict hop in the explicit route.
Type
TBD Path Key with IPv4 address
Length
The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length is always
8.
IPv4 address
An IPv4 address of the PCE that can decode this key. The
address used SHOULD be an address of the PCE that is always
Bradford, Vasseur, and Farrel 7
Draft-ietf-pce-path-key-00.txt May 2007
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.
PKS IPv6 sub-object
PKS Object-Class is to be assigned by IANA (recommended value=16)
PKS Object-Type is to be assigned by IANA (recommended value=2)
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (16 bytes) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
As above.
Type
TBD Path Key with IPv6 address
Length
The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length is always
20.
IPv6 address
An IPv6 address of the PCE that can decode this key. The
address used SHOULD be an 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.
4.2. PKS bit
[PCEP] specifies the RP object that is used to specify various
characteristics of the path computation request.
Bradford, Vasseur, and Farrel 8
Draft-ietf-pce-path-key-00.txt May 2007
In this document we define a new bit named the PKS bit defined as
follow:
PKS (PKS - 1 bit - Value=0x60): when set, the requesting PCC
requires the retrieval of a strict path segment that corresponds
to a PKS carried within the path computation request. The PKS bit
MUST be cleared when the path computation request is not related
to a CPS retrieval.
5. PCEP Mode of operation
The retrieval of the explicit path 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 PKS object and the
PKS bit of the RP object MUST the set.
If the receiving PCE cannot find any related strict path or the
retrieval of such strict path is not allowed by policy, the PCE
MUST send a PCRep message that contains a NO-PATH object.
Upon receipt of this negative reply, the requesting LSR MUST fail
the LSP setup and SHOULD use the procedures associated with loose
hop expansion failure [RFC3209].
6. Security Considerations
This document proposes tunneling secure topology information
across an untrusted AS, so the security considerations are many
and apply to PCEP and RSVP-TE.
Issues include:
- Security 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 DNS 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. These interactions
include the:
- PCC->PCE request
Bradford, Vasseur, and Farrel 9
Draft-ietf-pce-path-key-00.txt May 2007
- 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 pt-pt links. 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.
7. Manageability Considerations
To be detailed in a further revision of this document.
8. IANA considerations
IANA assigns value to PCEP parameters. Each PCEP object has an
Object-Class and an Object-Type.
Two new PCEP objects are defined in this document: the IPv4 PKS
and the IPv6 PKS objects.
Object-Class Name
16 PKS IPv4
Object-Type
1
Bradford, Vasseur, and Farrel 10
Draft-ietf-pce-path-key-00.txt May 2007
16 PKS IPv6
Object-Type
2
9. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology
described in this document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights. Information on the procedures with respect to rights
in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required
to implement this standard. Please address the information to the
IETF at ietf-ipr@ietf.org.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC
3209, December 2001.
[PCEP] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E.,
Bradford, Vasseur, and Farrel 11
Draft-ietf-pce-path-key-00.txt May 2007
Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation Element
(PCE) communication Protocol (PCEP)", draft-vasseur-pce-pcep,
work in progress.
[RSVP-PKS] Bradford, R., Vasseur, J.P., Farrel, A., "RSVP
Extensions for Path Key Support", draft-bradford-ccamp-path-key-
ero, work in progress.
[PCE-MONITORING] Vasseur, J.P, "A set of monitoring tools for Path
Computation Element based Architecture", draft-vasseur-pce-
monitoring, work in progress.
10.2. Informational References
[PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE) Architecture", RFC4655, September 2006.
[PD-PATH-COMP] Vasseur, J., et al "A Per-domain path computation
method for establishing Inter-domain Traffic Engineering (TE)
Label
Switched Paths (LSPs)", draft-ietf-ccamp-inter-domain-pd-path-
comp, work in progress.
[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.
11. Authors' Addresses:
Rich Bradford (Editor)
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough , MA - 01719
Bradford, Vasseur, and Farrel 12
Draft-ietf-pce-path-key-00.txt May 2007
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
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Bradford, Vasseur, and Farrel 13
Draft-ietf-pce-path-key-00.txt May 2007
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Bradford, Vasseur, and Farrel 14
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