OSPF A. Smirnov
Internet-Draft A. Retana
Updates: 5786 (if approved) M. Barnes
Intended status: Standards Track Cisco Systems, Inc.
Expires: July 30, 2017 January 26, 2017
OSPF Routing with Cross-Address Family MPLS Traffic Engineering Tunnels
draft-ietf-ospf-xaf-te-00
Abstract
When using Traffic Engineering (TE) in a dual-stack IPv4/IPv6 network
the Multiprotocol Label Switching (MPLS) TE Label Switched Paths
(LSP) infrastructure may be duplicated, even if the destination IPv4
and IPv6 addresses belong to the same remote router. In order to
achieve an integrated MPLS TE LSP infrastructure, OSPF routes must be
computed over MPLS TE tunnels created using information propagated in
another OSPF instance. This is solved by advertising cross-address
family (X-AF) OSPF TE information.
This document describes an update to RFC5786 that allows for the easy
identification of a router's local X-AF IP addresses.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 30, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
TE Extensions to OSPFv2 [RFC3630] and to OSPFv3 [RFC5329] have been
described to support intra-area TE in IPv4 and IPv6 networks,
respectively. In both cases the TE database provides a tight
coupling between the routed protocol and TE signaling information in
it. In other words, any use of the TE link state database is limited
to IPv4 for OSPFv2 [RFC2328] and IPv6 for OSPFv3 [RFC5340].
In a dual stack network it may be desirable to set up common MPLS TE
LSPs to carry traffic destined to addresses from different address
families on a router. The use of common LSPs eases potential
scalability and management concerns by halving the number of LSPs in
the network. Besides, it allows operators to group traffic based on
business characteristics and/or applications or class of service, not
constrained by the network protocol which carries it.
For example, an LSP created based on MPLS TE information propagated
by OSPFv2 instance can be defined to carry both IPv4 and IPv6
traffic, instead of having both OSPFv2 and OSPFv3 to provision a
separate LSP for each address family. Even if in some cases the
address family-specific traffic is to be separated, the calculation
from a common database may prove operationally beneficial.
A requirement when creating a common MPLS TE infrastructure is the
ability to reliably map the X-AF family addresses to the
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corresponding advertising tail-end router. This mapping is a
challenge because the LSAs containing the routing information are
carried in one OSPF instance while the TE calculation may be done
using a TE database from a different instance.
A simple solution to this problem is to rely on the Router ID to
identify a node in the corresponding OSPFv2 and OSPFv3 databases.
This solution would mandate both instances on the same router to be
configured with the same Router ID. However, relying on the
correctness of the configuration puts additional burden on network
management and adds cost to the operation of the network. The
network becomes even more difficult to manage if OSPFv2 and OSPFv3
topologies do not match exactly, for example if area borders are
drawn differently in the two protocols. Also, if the routing
processes do fall out of sync (having different Router IDs, even if
for local administrative reasons), there is no defined way for other
routers to discover such misalignment and to take any corrective
measures (such as to avoid routing through affected TE tunnels or
issuing warning to network management). The use of misaligned router
IDs may result in delivering the traffic to the wrong tail-end
router, which could lead to suboptimal routing or even traffic loops.
This document describes an update to [RFC5786] that allows for the
easy identification of a router's local X-AF IP addresses. Routers
using the Node Attribute TLV [RFC5786] can include non-TE enabled
interface addresses in their OSPF TE advertisements, and also use the
same sub-TLVs to carry X-AF information, facilitating the mapping
mentioned above.
The method described in this document can also be used to compute
X-AF mapping of egress LSR for sub-LSPs of a Point-to-Multipoint LSP
(see [RFC4461]). Considerations of using Point-to-Multipoint MPLS TE
for X-AF traffic forwarding is outside the scope of this
specification.
2. 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 [RFC2119].
3. Operation
[RFC5786] defined the Node IPv4 Local Address and Node IPv6 Local
Address sub-TLVs of the Node Attribute TLV for a router to advertise
additional local IPv4 and IPv6 addresses. To solve the problem
outlined in [RFC5786] OSPFv2 would advertise and use only IPv4
addresses and OSPFv3 would advertise and use only IPv6 addresses.
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This document updates [RFC5786] so that a router can also announce
one or more local X-AF addresses using the corresponding Local
Address sub-TLV. In other words, to implement the X-AF routing
technique proposed in this document, OSPFv2 will advertise the Node
IPv6 Local Address sub-TLV and OSPFv3 will advertise the Node IPv4
Local Address sub-TLV, possibly in addition to advertising other IP
addresses as documented by [RFC5786].
A node that implements X-AF routing SHOULD advertise in the
corresponding Node Local Address sub-TLV all X-AF IP addresses local
to the router that can be used by Constrained SPF (CSPF) to calculate
MPLS TE LSPs. In general, OSPF SHOULD advertise the IP address
listed in the Router Address TLV of the X-AF instance maintaining
MPLS TE database plus any additional local addresses advertised by
the X-AF OSPF instance in its Node Local Address sub-TLV.
Implementation MAY advertise other local X-AF addresses.
If the Node Attribute TLV carries both the Node IPv4 Local Address
sub-TLV and the Node IPv6 Local Address sub-TLV, then the X-AF
component must be considered for the consolidated calculation of MPLS
TE LSPs. Both instances may carry the required information, it is
left to local configuration to determine which database is used.
On Area Border Routers (ABR), each advertised X-AF IP address MUST be
advertised into at most one area. If OSPFv2 and OSPFv3 area borders
match (i.e. for each interface area number for OSPFv2 and OSPFv3
instances is numerically equal), then the X-AF addresses MUST be
advertised into the same area in both instances. This allows other
ABRs connected to the same set of areas to know with which area to
associate MPLS TE tunnels.
During the X-AF routing calculation, X-AF IP addresses are used to
map locally created LSPs to tail-end routers in the LSDB. The
mapping algorithm can be described as:
Walk the list of all MPLS TE tunnels for which the computing
router is a head-end. For each MPLS TE tunnel T:
1. If T's destination IP address is from the same address family as
the computing OSPF instance, then the tunnel must have been
signaled based on MPLS TE information propagated in the same OSPF
instance. Process the tunnel as per [RFC3630] or [RFC5329].
2. Otherwise it is a X-AF MPLS TE tunnel. Note tunnel's destination
IP address.
3. Walk the X-AF IP addresses in the LSDBs of all connected areas.
If a matching IP address is found, advertised by router R in area
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A, then mark the tunnel T as belonging to area A and terminating
on tail-end router R. Assign an intra-area SPF cost to reach
router R within area A as the IGP cost of tunnel T.
After completing this calculation, each TE tunnel is associated with
an area and tail-end router in terms of the routing LSDB of the
computing OSPF instance and has a metric.
Note that for clarity of description the mapping algorithm is
specified as a single calculation. Actual implementations for the
efficiency may choose to support equivalent mapping functionality
without implementing the algorithm exactly as it is described.
As an example lets consider a router in dual-stack network running
OSPFv2 and OSPFv3 for IPv4 and IPv6 routing correspondingly. Suppose
OSPFv2 instance is used to propagate MPLS TE information and the
router is configured to accept TE LSPs terminating at local addresses
198.51.100.1 and 198.51.100.2. Then the router will advertise into
OSPFv2 instance IPv4 address 198.51.100.1 in the Router Address TLV,
additional local IPv4 address 198.51.100.2 in the Node IPv4 Local
Address sub-TLV, plus other Traffic Engineering TLVs as required by
[RFC3630]. If OSPFv3 instance in the network is enabled for X-AF TE
routing (that is, to use for IPv6 routing MPLS TE LSPs computed by
OSPFv2), then the OSPFv3 instance of the router will advertise the
Node IPv4 Local Address sub-TLV listing local IPv4 addresses
198.51.100.1 and 198.51.100.2. Other routers in the OSPFv3 network
will use this information to reliably identify this router as egress
LSR for MPLS TE LSPs terminating at either 198.51.100.1 or
198.51.100.2.
4. Backward Compatibility
Node Attribute TLV and Node Local Address sub-TLVs and their usage
are defined in [RFC5786] and updated by [RFC6827]. Way of using
these TLVs as specified in this document is fully backward compatible
with previous standard documents.
An implementation processing Node Attribute TLV MUST interpret its
content as follows:
o If the Node Attribute TLV contains Local TE Router ID sub-TLV then
this Node Attribute TLV MUST be treated as carrying routing
information for ASON (Automatically Switched Optical Network) and
processed as specified in [RFC6827].
o Otherwise Node Attribute TLV contains one or more instance(s) of
Node IPv4 Local Address and/or Node IPv6 Local Address sub-TLVs.
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Meaning of each Local Address sub-TLV has to be identified
separately.
* If Node Local Address sub-TLV belongs to the same address
family as instance of OSPF protocol advertising it then address
carried in the sub-TLV MUST be treated as described in
[RFC5786].
* Otherwise the address is used for X-AF tunnel tail-end mapping
as defined by this document.
5. Security Considerations
This document introduces no new security concerns. Security
considerations of using Node Attribute TLV are discussed in
[RFC5786].
6. IANA Considerations
This document has no IANA actions.
7. Acknowledgements
The authors would like to thank Peter Psenak and Eric Osborne for
early discussions and Acee Lindem for discussing compatibility with
ASON extensions.
We would also like to thank the authors of RFC5786 for laying down
the foundation for this work.
8. References
8.1. Normative References
[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>.
[RFC5786] Aggarwal, R. and K. Kompella, "Advertising a Router's
Local Addresses in OSPF Traffic Engineering (TE)
Extensions", RFC 5786, DOI 10.17487/RFC5786, March 2010,
<http://www.rfc-editor.org/info/rfc5786>.
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8.2. Informative References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<http://www.rfc-editor.org/info/rfc3630>.
[RFC4461] Yasukawa, S., Ed., "Signaling Requirements for Point-to-
Multipoint Traffic-Engineered MPLS Label Switched Paths
(LSPs)", RFC 4461, DOI 10.17487/RFC4461, April 2006,
<http://www.rfc-editor.org/info/rfc4461>.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<http://www.rfc-editor.org/info/rfc5329>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>.
[RFC6827] Malis, A., Ed., Lindem, A., Ed., and D. Papadimitriou,
Ed., "Automatically Switched Optical Network (ASON)
Routing for OSPFv2 Protocols", RFC 6827,
DOI 10.17487/RFC6827, January 2013,
<http://www.rfc-editor.org/info/rfc6827>.
Authors' Addresses
Anton Smirnov
Cisco Systems, Inc.
De kleetlaan 6a
Diegem 1831
Belgium
Email: as@cisco.com
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Alvaro Retana
Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
Email: aretana@cisco.com
Michael Barnes
Cisco Systems, Inc.
510 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: mjbarnes@cisco.com
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