Network Working Group J. Dong
Internet-Draft M. Chen
Intended status: Standards Track D. Dhody
Expires: March 4, 2016 Huawei Technologies
J. Tantsura
Ericsson
September 1, 2015
BGP Extensions for Path Computation Element (PCE) Discovery
draft-dong-pce-discovery-proto-bgp-03
Abstract
In networks where Path Computation Element (PCE) is used for
centralized path computation, it is desirable for Path Computation
Clients (PCCs) to automatically discover a set of PCEs and select the
suitable ones to establish the PCEP session. RFC 5088 and RFC 5089
define the PCE discovery mechanisms based on Interior Gateway
Protocols (IGP). This document describes several scenarios in which
the IGP based PCE discovery mechanisms cannot be used directly. This
document specifies the BGP extensions for PCE discovery in these
scenarios. The BGP based PCE discovery mechanism is complementary to
the existing IGP based mechanisms.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 4, 2016.
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Copyright Notice
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document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Carrying PCE Discovery Information in BGP . . . . . . . . . . 4
2.1. PCE Address Information . . . . . . . . . . . . . . . . . 4
2.2. PCE Discovery TLVs . . . . . . . . . . . . . . . . . . . 5
3. Operational Considerations . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
In network scenarios where Path Computation Element (PCE) is used for
centralized path computation, it is desirable for Path Computation
Clients (PCCs) to automatically discover a set of PCEs and select the
suitable ones to establish the PCEP session. [RFC5088] and [RFC5089]
define the PCE discovery mechanisms based on Interior Gateway
Protocols (IGP). Those IGP based mechanisms may not work in several
scenarios where the PCEs do not participate in the IGP, and it is
difficult for PCEs to participate in multiple IGP domains where PCE
discovery is needed.
In some scenarios, Backward Recursive Path Computation (BRPC)
[RFC5441] can be used by cooperating PCEs to compute inter-domain
path, in which case these cooperating PCEs should be known to each
other in advance. In case of inter-AS networks where the PCEs do not
participate in a common IGP, the existing IGP discovery mechanism
cannot be used to discover the PCEs in other domains.
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In the Hierarchical PCE scenario [RFC6805], the child PCEs need to
know the address of the parent PCEs. This cannot be achieved through
IGP based discovery, as normally the child PCEs and the parent PCE
are under different administration and reside in different domains.
Besides, as BGP could be used for north-bound distribution of routing
and Label Switched Path (LSP) information to PCE as described in
[I-D.ietf-idr-ls-distribution] [I-D.ietf-idr-te-lsp-distribution] and
[I-D.ietf-idr-te-pm-bgp], PCEs can obtain the routing information
without participating in IGP. In this scenario, some other PCE
discovery mechanism is needed.
A detailed set of requirements for a PCE discovery mechanism are
provided in [RFC4674].
This document proposes to extend BGP for PCE discovery in the above
scenarios. In networks where BGP-LS is used for the north-bound
routing information distribution to PCE, the BGP based PCE discovery
can reuse the existing BGP sessions and mechanisms to achieve PCE
discovery. It should be noted that in each IGP domain, the IGP based
PCE discovery mechanism may be used in conjunction with the BGP based
PCE discovery. Thus the BGP based PCE discovery is complementary to
the existing IGP based mechanisms.
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+-----------+
| PCE |
+-----------+
|
v
+-----------+
| BGP | +-----------+
| Speaker | | PCE |
+-----------+ +-----------+
| | | |
| | | |
+---------------+ | +-------------------+ |
v v v v
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
| & PCC | | & PCC | | |
+-----------+ +-----------+ +-----------+
|
| via
| IGP
v
+-----------+
| PCC |
+-----------+
Figure 1: BGP for PCE discovery
As shown in the network architecture in Figure 1, BGP is used for
both routing information distribution and PCE information discovery.
The routing information is collected from the network elements and
distributed to PCE, while the PCE discovery information is advertised
from PCE to PCCs, or between different PCEs. The PCCs maybe co-
located with the BGP speakers as shown in Figure 1. The IGP based
PCE discovery mechanism may be used for the distribution of PCE
discovery information in IGP domain.
2. Carrying PCE Discovery Information in BGP
2.1. PCE Address Information
The PCE discovery information is advertised in BGP UPDATE messages
using the MP_REACH_NLRI and MP_UNREACH_NLRI attributes [RFC4760].
The AFI and SAFI defined in [I-D.ietf-idr-ls-distribution] are re-
used, and a new NLRI Type is defined for PCE discovery information as
below:
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o Type = TBD: PCE Discovery NLRI
The format of PCE Discovery NLRI is shown in the following figure:
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
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ PCE-Address (4 or 16 octets) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. PCE Discovery NLRI
The 'Protocol-ID' field SHOULD be set to a new value which indicates
the information source protocol is PCE.
+-------------+----------------------------------+
| Protocol-ID | NLRI information source protocol |
+-------------+----------------------------------+
| TBD | PCE |
+-------------+----------------------------------+
As defined in [I-D.ietf-idr-ls-distribution], the 64-Bit 'Identifier'
field is used to identify the "routing universe" where the PCE
belongs.
2.2. PCE Discovery TLVs
The detailed PCE discovery information is carried in the BGP-LS
attribute [I-D.ietf-idr-ls-distribution] with a new "PCE Discovery
TLV", which contains a set of sub-TLVs for specific PCE discovery
information. The PCE Discovery TLV and sub-TLVs SHOULD only be used
with the PCE Discovery NLRI.
The format of the PCE Discovery TLV is shown as below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ PCE Discovery Sub-TLVs (variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. PCE Discovery TLV
The PCE Discovery sub-TLVs are listed as below. The format of the
PCE Discovery sub-TLVs are consistent with the IGP PCED sub-TLVs as
defined in [RFC5088] and [RFC5089]. The PATH-SCOPE sub-TLV MUST
always be carried in the PCE Discovery TLV. Other PCE Discovery sub-
TLVs are optional and may facilitate the PCE selection process on the
PCCs.
Type | Length | Name
------+------------+--------------------------------
TBD | 3 | PATH-SCOPE sub-TLV
TBD | variable | PCE-CAP-FLAGS sub-TLV
TBD | variable | OSPF-PCE-DOMAIN sub-TLV
TBD | variable | IS-IS-PCE-DOMAIN sub-TLV
TBD | variable | OSPF-NEIG-PCE-DOMAIN sub-TLV
TBD | variable | IS-IS-NEIG-PCE-DOMAIN sub-TLV
More PCE Discovery sub-TLVs may be defined in future and the format
SHOULD be in line with the new sub-TLVs defined for IGP based PCE
discovery.
3. Operational Considerations
Existing BGP operational procedures apply to the advertisement of PCE
discovery information. This information is treated as pure
application level data which has no immediate impact on forwarding
states. Normal BGP path selection can be applied to PCE Discovery
NLRI only for the information propagation in the network, while the
PCE selection on the PCCs would be based on the information carried
in the PCE Discovery TLV.
The PCE discovery information is considered relatively stable and
does not change frequently, thus this information will not bring
significant impact on the amount of BGP updates in the network.
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4. IANA Considerations
IANA needs to assign a new NLRI Type for 'PCE Discovery NLRI' from
the "BGP-LS NLRI-Types" registry.
IANA needs to assign a new Protocol-ID for "PCE" from the "BGP-LS
Protocol-IDs" registry.
IANA needs to assign a new TLV code point for 'PCE Discovery TLV'
from the "node anchor, link descriptor and link attribute TLVs"
registry.
IANA needs to create a new registry for "PCE Discovery Sub-TLVs".
The registry will be initialized as shown in section 2.2 of this
document.
5. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the BGP security model. See the 'Security Considerations'
section of [RFC4271] for a discussion of BGP security. Also refer to
[RFC4272] and [RFC6952] for analysis of security issues for BGP.
6. Acknowledgements
The authors would like to thank Zhenbin Li and Hannes Gredler for
their discussion and comments.
7. References
7.1. Normative References
[I-D.ietf-idr-ls-distribution]
Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
Ray, "North-Bound Distribution of Link-State and TE
Information using BGP", draft-ietf-idr-ls-distribution-11
(work in progress), June 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
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[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>.
[RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
January 2008, <http://www.rfc-editor.org/info/rfc5088>.
[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
January 2008, <http://www.rfc-editor.org/info/rfc5089>.
7.2. Informative References
[I-D.ietf-idr-te-lsp-distribution]
Dong, J., Chen, M., Gredler, H., Previdi, S., and J.
Tantsura, "Distribution of MPLS Traffic Engineering (TE)
LSP State using BGP", draft-ietf-idr-te-lsp-
distribution-03 (work in progress), May 2015.
[I-D.ietf-idr-te-pm-bgp]
Wu, Q., Previdi, S., Gredler, H., Ray, S., and J.
Tantsura, "BGP attribute for North-Bound Distribution of
Traffic Engineering (TE) performance Metrics", draft-ietf-
idr-te-pm-bgp-02 (work in progress), January 2015.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>.
[RFC4674] Le Roux, J., Ed., "Requirements for Path Computation
Element (PCE) Discovery", RFC 4674, DOI 10.17487/RFC4674,
October 2006, <http://www.rfc-editor.org/info/rfc4674>.
[RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
"A Backward-Recursive PCE-Based Computation (BRPC)
Procedure to Compute Shortest Constrained Inter-Domain
Traffic Engineering Label Switched Paths", RFC 5441,
DOI 10.17487/RFC5441, April 2009,
<http://www.rfc-editor.org/info/rfc5441>.
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[RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the
Path Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
DOI 10.17487/RFC6805, November 2012,
<http://www.rfc-editor.org/info/rfc6805>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<http://www.rfc-editor.org/info/rfc6952>.
Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
Mach(Guoyi) Chen
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: mach.chen@huawei.com
Dhruv Dhody
Huawei Technologies
Leela Palace
Bangalore, Karnataka 560008
India
Email: dhruv.ietf@gmail.com
Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
US
Email: jeff.tantsura@ericsson.com
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