Network Working Group V. Lopez
Internet-Draft O. Gonzalez de Dios
Intended status: Informational Telefonica I+D
Expires: January 2, 2015 D. King
Old Dog Consulting
S. Previdi
Cisco Systems, Inc.
J. Tantsura
Ericsson
July 1, 2014
Traffic Engineering Database dissemination for Hierarchical PCE
scenarios
draft-lopez-pce-hpce-ted-02
Abstract
The PCE architecture is well-defined and may be used to compute the
optimal path for LSPS across domains in MPLS-TE and GMPLS networks.
The Hierarchical Path Computation Element (H-PCE) [RFC6805] was
developed to provide an optimal path when the sequence of domains is
not known in advance. The procedure and mechanism for populating the
Traffic Engineering Database (TED) with domain topology and link
information used in H-PCE-based path computations is open to
interpretation. This informational document describes how topology
dissemination mechanisms may be used to provide TE information
between Parent and Child PCEs (within the H-PCE context). In
particular, it describes how BGP-LS might be used to provide inter-
domain connectivity. This document is not intended to define new
extensions, it demonstrates how existing procedures and mechanisms
may be used.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on January 2, 2015.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Parent PCE Domain Topology . . . . . . . . . . . . . . . 3
1.2. Parent PCE TED requirements . . . . . . . . . . . . . . . 4
2. H-PCE Domain Topology Dissemination and Construction Methods 4
3. H-PCE architecture using BGP-LS . . . . . . . . . . . . . . . 5
4. Including inter-domain connectivity in BGP-LS . . . . . . . . 8
4.1. Mapping from OSPF-TE . . . . . . . . . . . . . . . . . . 9
4.1.1. Node Descriptors . . . . . . . . . . . . . . . . . . 9
4.1.2. Link Descriptors . . . . . . . . . . . . . . . . . . 9
4.1.3. Mapping OSPF TE parameters into BGP-LS attribute . . 10
4.2. Mapping from ISIS-TE . . . . . . . . . . . . . . . . . . 10
5. Manageability Considerations . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
In scenarios with multiple domains in both MPLS-TE and GMPLS
networks, the hierarchical Path Computation Element (H-PCE)
Architecture, defined in [RFC6805], allows to obtain the optimum end-
to-end path. The architecture exploits a hierarchical relation among
domains.
[RFC6805] defines the architecture and requirements for the end-to-
end path computation across domains. The solution draft for the
H-PCE [I-D.draft-ietf-pce-hierarchy-extensions] is focused on the
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PCEP protocol extensions to support such H-PCE procedures, including
negotiation of capabilities and errors. However, neither the
architecture nor the solution draft specify which mechanism must to
be used to build and populate the parent PCE (pPCE) Traffic
Engineering Database (TED).
The H-PCE architecture documents define the minimum content needed in
the traffic engineering database required to compute paths. The
information required by parent TEDB are identified in [RFC6805] and
further elaborated in
[I-D.draft-ietf-pce-inter-area-as-applicability]. For instance,
[RFC6805] and [I-D.draft-ietf-pce-inter-area-as-applicability]
suggest that BGP-LS could be used as a "northbound" TE advertisement.
This means that a PCE does not need to listen IGP in its domain, but
its TED is populated by messages received (for example) from a Route
Reflector. [I-D.draft-ietf-idr-te-pm-bgp] extends BGP-LS to
disseminate traffic engineering information. The parameters
considered are: delay, packet loss and bandwidth.
This document highlights the applicability of BGP-LS to the
dissemination of domain topology within the H-PCE architecture. In
particular, it describes how can BGP-LS be used to send the inter-
domain connectivity. It also shows how can OSPF-TE and ISIS-TE
updates be mapped into BGP-LS.
Note that this document is not intended to define new protocol
extensions, it is an informational document and where required it
highlights where existing mechanisms and protocols may be applied.
1.1. Parent PCE Domain Topology
The pPCE maintains a domain topology map of the child domains and
their interconnectivity. This map does not include any visibility
into the child domains. Where inter-domain connectivity is provided
by TE links, the capabilities of those links may also be known to the
pPCE. The pPCE maintains a TED for the parent domain, the nodes in
the parent domain are abstractions of the cPCE domains (connected by
real or virtual TE links), but the pPCE domain may also include real
nodes and links.
The procedure and protocol mechanism for disseminating and
construction of the pPCE TED may be provided using a number of
mechanisms, including manually configuring the necessary information
or automated using a separate instance of a routing protocol to
advertise the domain interconnectivity. Since inter-domain TE links
can be advertised by the IGPs operating in the child domains, this
information could then be exported to the parent PCE either by the
child PCEs or using north-bound export mechanisms.
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1.2. Parent PCE TED requirements
The information that would be exchanged includes:
o Identifier of advertising child PCE.
o Identifier of PCE's domain.
o Identifier of the link.
o TE properties of the link (metrics, bandwidth).
o Other properties of the link (technology-specific).
o Identifier of link endpoints.
o Identifier of adjacent domain.
2. H-PCE Domain Topology Dissemination and Construction Methods
A variety of methods exist to provide are different alternatives so
the parent PCE can get the topological information from the child
PCEs (cPCEs):
o Statically configure all inter-domain link and topology
information.
o Membership of an IGP instance. The necessary topological
information could be disseminated by joining the IGP instance of
each child PCE domain. However, by doing so, it would break the
domain confidentiality principles and is subject to scalability
issues.
o PCEP Notification Messages. Another solution is to send the
interconnection information between domains using PCEP
Notifications (see section 4.8.4 of [RFC6805]). One approach,
followed in research work, is embedding in PCEP Notifications the
Inter-AS OSPF-TE Link State Advertisements (LSA) to send the
Inter-Domain Link information from child PCEs to the parent PCE
and to send reachability information (list of end-points in each
domain). However, it is argued that the utilization of PCEP to
disseminate topology is beyond scope of the protocol.
o Separate IGP instance. [RFC6805] points out that in models such
as ASON it is possible to consider a separate instance of an IGP
running within the parent domain where the participating protocol
speakers are the nodes directly present in that domain and the
PCEs (parent and child PCEs).
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o Use north-bound distribution of TE information. The North-Bound
Distribution of Link-State and TE Information using BGP has been
recently propose in the IEFT [I-D.draft-ietf-idr-ls-distribution].
This approach is known as BGP-LS and defines a mechanism by which
links state and traffic engineering information can be collected
from networks and exported to external elements using the BGP
routing protocol. By using BGP-LS as northbound distribution
mechanism, there would be a BGP speaker in each domains that sends
the necessary information to a BGP speaker in the parent domain.
This architecture is further elaborated in this document.
3. H-PCE architecture using BGP-LS
As mentioned in [I-D.draft-dugeon-pce-ted-reqs] PCE has to retrieve
Traffic Engineering (TE) information to carry out its path
computation. This is required not only for intra-domain information,
which can be got using IGP (like OSPF-TE or ISIS-TE), but also for
inter-domain information in the Hierarchical PCE (H-PCE)
architecture.
Figure 1 shows an example of a H-PCE architecture. In this example,
there is a parent PCE and three child PCEs, and they are organized in
multiple domains. The parent PCE does not have information of the
whole network, but is only aware of the connectivity among the
domains and provides coordination to the child PCEs. Figure 2 shows
which is the visibility that parent PCE has from the network
according to the definition in [RFC6805].
Thanks to this topological information, when there is a request to a
child PCE with the destination in another domain, this path request
is sent to the parent PCE, which selects a set of candidate domain
paths and sends requests to the child PCEs responsible for these
domains. Then, the parent PCE selects the best solution and it is
transmitted to the source PCE.
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-----------------------------------------------------------------
| Parent PCE Domain |
| ----- |
| |pPCE | |
| ----- |
| |
| ---------------- ---------------- ---------------- |
| | Domain 1 | | Domain 2 | | Domain 3 | |
| | | | | | | |
| | ------ | | ------ | | ------ | |
| | |cPCE 1| | | |cPCE 2| | | |cPCE 3| | |
| | ------ | | ------ | | ------ | |
| | | | | | | |
| | ----| |---- ----| |---- | |
| | |BN11+---+BN21| |BN23+---+BN31| | |
| | ----| |---- ----| |---- | |
| | | | | | | |
| | ----| |---- ----| |---- | |
| | |BN12+---+BN22| |BN24+---+BN32| | |
| | ----| |---- ----| |---- | |
| | | | | | | |
| ---------------- ---------------- ---------------- |
-----------------------------------------------------------------
Figure 1: Example of Hierarchical PCE architecture
----------------------------
| Parent PCE view |
| ---- |
| |pPCE| |
| ---- |
| |
| ---- ---- ---- |
| | |---| |---| | |
| | D1 | | D2 | | D3 | |
| | |---| |---| | |
| ---- ---- ---- |
----------------------------
Figure 2: Parent PCE topology information
Thanks to the dissemination of inter-domain adjacency information
from each cPCE to the pPCE, the pPCE can have a view of reachability
between the domains. The H-PCE architecture with BGP-LS is shown in
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Figure 3. Each domain has a cPCE that is able to compute paths in
the domain. This child PCE has access to a domain TED, which is
built using IGP information. In each domain, a BGP speaker has
access to such domain TED and acts as BGP-LS Route Reflector to
provide network topology to the pPCE. Next to the pPCE, there is a
BGP speaker that maintains a BGP session with each of the BGP
speakers in the domains to receive the topology and build the parent
TED. A policy can be applied to the BGP-LS speakers to decide which
information is sent to its peer speaker. The minimum amount of
information that needs to be exchanged is the inter-domain
connectivity, including the details of the Traffic Engineering Inter-
domain Links [RFC6805]. With this information, the parent PCE is
able to have access to a domain topology map and its connectivity.
Additionally, the BGP-LS speaker can be configured to send some
intra-domain information for virtual or candidate paths with some TE
information. In this case, the parent PCE has access to an extended
database, with visibility of both intra-domain and inter-domain
information and can compute the sequence of domains with better
accuracy.
BGP-LS [I-D.draft-ietf-idr-ls-distribution] extends the BGP Update
messages to advertise link-state topology thanks to new BGP Network
Layer Reachability Information (NLRI). The Link State information is
sent in two BGP attributes, the MP_REACH (defined in [RFC4670]) and a
LINK_STATE attribute (defined in
[I-D.draft-ietf-idr-ls-distribution]). To describe the inter domain
links, in the MP_REACH attribute, a Link NLRI can be used with the
local node descriptors the address of the source, and in the remote
descriptors, the address of the destination of the link. The Link
Descriptors field has a TLV (Link Local/Remote Identifiers), which
carries the prefix of the Unnumbered or Numbered Interface. In case
of the message informs about an intra-domain link, the standard
traffic engineering information is included in the LINK_STATE
attribute.
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----------------------------------------------------------------------
| Parent PCE Domain |
| ------- ----- ----- |
| -------+BGP-LS +---+ TED +--+pPCE | |
| / |Speaker| ----- ----- |
| / --+---+ |
| / | \_________________
| / | \
| ------------/-------- ----+------------ ------+------------ |
| | Domain 1 / | | | Domain 2 | | | Domain 3 | |
| | / | | | | | | | |
| | ------+ | | -+----- | | ---+--- | |
| | |BGP-LS | | | |BGP-LS | | | |BGP-LS | | |
| | |Speaker| | | |Speaker| | | |Speaker| | |
| | ---+--- | | ---+--- | | ---+--- | |
| | | | | | | | | | |
| | ---+--- ------ | | ---+-- ------ | | ---+--- ------ | |
| | | TED +-+cPCE 1| | | | TED +-+cPCE| | | | TED +-+cPCE 1| | |
| | ---+--- ------ | | ---+-- ------ | | ---+--- ------ | |
| | | | | | | | | | |
| | ---+--- | | ---+--- | | ---+--- | |
| | | IGP | | | | IGP | | | | IGP | | |
| | | Peer | | | | Peer | | | | Peer | | |
| | ------- | | ------- | | ------- | |
| | | | | | | | | | |
| ------+--------------- -----+----------- ------+------------ |
| | | | |
| ------------------- ---------------- ------------------- |
| | Domain 1 | | Domain 2 | | Domain 3 | |
| ------------------- ---------------- ------------------- |
----------------------------------------------------------------------
Figure 3: Example of Hierarchical PCE architecture with BGP-LS
4. Including inter-domain connectivity in BGP-LS
In order for the parent PCE to carry out the path computation tasks
it needs the inter-domain topology between the child domain
scenarios. This topology is learnt through IGP by each BGP-LS
speaker. The Traffic Engineering extensions (OSPF-TE or ISIS-TE)
allow IGP to carry link state information that can be used in
optimizing technics such as the PCE algorithms. However, the parent
PCE does not require such TE information, but just connectivity
between the domains. However, TE information within the domain could
be disseminated to the parent PCE to reduce the queries to the child
PCEs.
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4.1. Mapping from OSPF-TE
Carrying TE information in OSPF is a well-known standardized feature
[RFC3630]. This section explains how this information can be
exported outside one IGP domain using BGP-LS. BGP-LS extends the BGP
Update messages to advertise link-state topology thanks to the new
BGP Network Layer Reachability Information (NLRI) and BGP-LS
attribute.
The BGP NLRI carries the descriptors used to define the element in
question (e.g. link or node) and the BGP-LS attribute carries the
chosen parameters to characterize the described element. Information
is codified using multiple TLV triplets just as the ones used in
OSPF-TE making it easy to integrate. For the purpose of this
document, we consider a scenario where there is an origin (router)
with the correspondent IPv4, a destination with its IPv4 and a link
having the following TE parameters: maximum BW, maximum reservable BW
and unreserved BW.
4.1.1. Node Descriptors
In the OSPF packet, there are two fields that tell us the origin and
destination node IDs. The origin IP is the Source OSPF Router ID in
the OSPF header and this is mapped into the IGP Router ID subTLV
inside the Local Node Descriptors field
[I-D.draft-ietf-idr-ls-distribution]. The destination IP is found as
the Link ID field in the MPLS LSA in OSPF. This is mapped into the
correspondent IGP Router ID in the Remote Node Descriptors field
[I-D.draft-ietf-idr-ls-distribution].
There are other subTLVs inside the Local/Remote Node Descriptors but
they are not relevant for this document.
4.1.2. Link Descriptors
The only two TLVs in the Link Descriptors field to map from OSPF are
the local and remote interface addresses. This information is mapped
directly from the Local/Remote Interface address TLV carried in the
MPLS LSA of OSPF into the Local/Remote Interface address subTLV of
the Link Descriptors field.
The same procedure must be applied for unnumbered interfaces but
utilizing the Link Local/Remote Identifiers TLV.
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4.1.3. Mapping OSPF TE parameters into BGP-LS attribute
As mentioned before, these parameters are not required in the H-PCE
scenario. They are just required to reduce the number of queries to
the children PCEs. The parent PCE can use bandwidth information
between two domains to request for some possible connections instead
of all.
The BGP-LS attribute will be a set of TLV triplets carrying the
desired TE parameters learnt by OSPF. Bandwidth parameters are used
to illustrate the example but they are many more (like, available
labels).
The BGP-LS attribute is mapped in the following way. The TLVs
carried in the MPLS-TE LSA in OSPF are directly translated into the
equivalent TLVs in BGP-LS. As such, the Unreserved BW TLV in OSPF is
mapped into the Unreserved BW TLV in BGP-LS. The same happens with
the Maximum BW TLV and the Maximum Reservable BW TLV.
4.2. Mapping from ISIS-TE
TBD
5. Manageability Considerations
TBD
6. Security Considerations
TBD
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
[RFC4670] Nelson, D., "RADIUS Accounting Client MIB for IPv6", RFC
4670, August 2006.
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[RFC6805] King, D. and A. Farrel, "The Application of the Path
Computation Element Architecture to the Determination of a
Sequence of Domains in MPLS and GMPLS", RFC 6805, November
2012.
7.2. Informative References
[I-D.draft-dugeon-pce-ted-reqs]
Dugeon, O., Meuric, J., Douville, R., Casellas, R., and O.
Gonzalez de Dios, "Path Computation Element (PCE) Traffic
Engineering Database (TED) Requirements", February 2014.
[I-D.draft-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", November 2013.
[I-D.draft-ietf-idr-te-pm-bgp]
Wu, Q., Wang, D., Previdi, S., Gredler, H., and S. Ray,
"BGP attribute for North-Bound Distribution of Traffic
Engineering (TE) performance Metrics", January 2014.
[I-D.draft-ietf-pce-hierarchy-extensions]
Zhang, F., Zhao, Q., Gonzalez de Dios, O., Casellas, R.,
and D. King, "Extensions to Path Computation Element
Communication Protocol (PCEP) for Hierarchical Path
Computation Elements (PCE)", July 2013.
[I-D.draft-ietf-pce-inter-area-as-applicability]
King, D., Meuric, J., Dugeon, O., Zhao, Q., and O.
Gonzalez de Dios, "Applicability of the Path Computation
Element to Inter-Area and Inter-AS MPLS and GMPLS Traffic
Engineering", February 2013.
Authors' Addresses
Victor Lopez
Telefonica I+D
Don Ramon de la Cruz 82-84
Madrid 28045
Spain
Phone: +34913128872
Email: vlopez@tid.es
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Oscar Gonzalez de Dios
Telefonica I+D
Don Ramon de la Cruz 82-84
Madrid 28045
Spain
Phone: +34913128832
Email: ogondio@tid.es
Daniel King
Old Dog Consulting
UK
Email: daniel@olddog.co.uk
Stefano Previdi
Cisco Systems, Inc.
Via Del Serafico 200
Rome 00144
IT
Email: sprevidi@cisco.com
Jeff Tantsura
Ericsson
USA
Email: jeff.tantsura@ericsson.com
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