One document matched: draft-iwijnand-mpls-mldp-multi-topology-00.txt
MPLS Working Group IJsbrand Wijnand
Internet Draft Cisco Systems, Inc.
Intended status: Standards Track
Expires: May 13, 2012 Kamran Raza
Cisco Systems, Inc.
November 14, 2011
mLDP Extensions for Multi Topology Routing
draft-iwijnand-mpls-mldp-multi-topology-00.txt
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Abstract
The Multi-Topology Routing (MTR) enables service differentiation
through class-based forwarding. IGP protocols (OSPF and IS-IS) have
already been extended to setup MTR. In order to deploy mLDP in an
MTR setup, mLDP is also required to become topology-aware. This
document specifies extensions to mLDP to support Multi-Topology
Routing.
Table of Contents
1. Glossary ..........................................................2
2. Introduction ......................................................3
3. Conventions used in this document .................................4
4. MT-Scoped mLDP FEC ................................................4
4.1.1 New MT IP Address Families .................................4
4.1.2 MT MP FEC Element ..........................................5
4.2 Topology IDs ...................................................6
5. Multipoint MT Capability...........................................7
6. MT Applicability on FEC-based features ............................8
6.1 Typed Wildcsrd MP FEC Elements ................................8
6.2 End-of-LIB .....................................................8
7. Topology-Scoped Forwarding ........................................9
7.1 Upstream LSR selection .........................................9
7.2 Downstream forwarding interface ................................9
8. Security Considerations ...........................................9
9. IANA Considerations ..............................................10
10. References ......................................................10
9.1. Normative References .........................................10
9.2. Informative References .......................................11
10. Acknowledgments .................................................11
1. Glossary
MT - - Multi-Topology
MT-ID Multi-Topology Identifier
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MTR - - Multi-Topology Routing
IGP - - Interior Gateway Protocol
mLDP - - Multi-point LDP
P2MP - - Point-to-Multipoint
MP2MP - - Multipoint-to-Multipoint
MP - Multi-point (P2MP or MP2MP)
LSP - - Label Switched Path
2. Introduction
The Multi-Topology Routing (MTR) enables service differentiation
through class-based forwarding. For example, MTR can be used to
define separate IP topologies for voice, video, and data traffic
classes. To support MTR, an IGP maintains independent IP topologies,
termed as "Multi-Topologies" (MT), and computes/installs routes per
topology. OSPF extensions [RFC4915] and ISIS extensions [RFC5120]
specify the MT extensions under respective IGP. To support IGP MT,
similar extensions [MT-LDP] have been proposed in LDP to make LDP
MT-aware, and be able to setup unicast Label Switched Paths (LSPs)
along IGP MT routing paths.
Multi-point LDP (mLDP) refers to extensions in LDP to setup multi-
point LSPs, point-to-multipoint (P2MP) or multipoint-to-multipoint
(MP2MP), by means of set of extensions and procedures defined in
[RFC6388]. In order to work in an MTR setup to take advantage of
MTs, it is a natural extension to make mLDP become MT-aware. This
document specifies the extensions to mLDP to support IGP Multi-
Topology Routing (MTR).
[Editor Note: This document will be updated and synchronized with MT
LDP [MT-LDP] specification as/when MT LDP specification is updated]
3. 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].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
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4. MT-Scoped mLDP FECs
The Multi-Topology Identifier (MTID) is an identifier that is used
to associate an MP LSP with a certain MTR topology. This identifier
is part of the mLDP FEC encoding. It is part of the FEC encoding
because LDP peers may want to setup an MP LSP via their own defined
MTR policy. In order to avoid conflicting MTR policies for the same
mLDP FEC, the MTID needs to be a part of the FEC, so that different
MTID values will result in unique MP-LSP FEC elements.
Since the MTID is part of the FEC, it will apply to all the LDP
messages that potentially include an mLDP FEC element.
Following subsections propose the extensions to bind an mLDP FEC to
a topology.
4.1.1. New MT IP Address Families
To extend IP address families for MT, we propose two new Address
Families named "MT IP" and "MT IPv6" that can be used to specify IP
prefixes within a topology scope. The format of the data associated
with these new Address Family is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (IP) Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MT IP Address Families Data Format
Where "(IP) Prefix" is an IPv4 and IPv6 address for "MT IP" and "MT
IPv6" AF respectively, and the field "MT-ID" corresponds to 16-bit
Topology ID for given prefix. The Address Family length incorporates
both the (IP) Prefix field, as well as following 4-octets for MT.
For MT IP and MT IPv6 AF, the AF length is 8 and 20 octets
respectively.
4.1.2. MT MP FEC Element
Base mLDP specification [RFC6388] defines MP FEC Element as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MP FEC type | AF (IP/IPv6) | AF Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Root Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MP FEC Element Format [RFC6388]
Where "Root Node Address" encoding is as defined for given "Address
Family", and whose length (in octets) is specified by the "AF
Length" field.
To extend MP FEC elements for MT, the MTID is an identifier that is
relevant in the context of the root address of the MP LSP. The MTID
identifier determines in which topology the root address needs to be
resolved. Since the MTID should be considered part of the mLDP FEC,
the most natural place to encode the MTID is as part of the root
address. For that reason we are proposing to use new MT IP Address
Family as defined in Section 4.1.1.
For MT mLDP, the MP FEC element's "Address Family" field will be set
to "MT IP" or "MT IPv6", and the FEC element will be encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MP FEC type | AF (MT IP/ MTIPv6) | AF Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Root Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: MT-Scoped MP FEC Element Format
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In the context of this document, the applicable LDP FECs for MT mLDP
include:
o MP FEC Elements:
o P2MP (0x6)
o MP2MP Upstream (0x7)
o MP2MP Downstream (0x8)
o Typed Wildcard FEC Element(0x5)
In case of "Typed Wildcard FEC Element", the sub FEC MUST be one of
the MP FECs listed above.
This specification allows the use of Topology-scoped mLDP FECs in
LDP label and notification messages, as applicable.
4.2. Topology IDs
This document assumes the same definitions and procedures associated
with MT-ID as defined in [MT-LDP] specification. Additionally, it
defines following special topology values:
Default Topology (0x0): Used for backward compatibility)
Wildcard Topology (0xffff): Used for wildcard label operations.
5. Multipoint MT Capability
"Multipoint MT Capability" is a new LDP capability, defined in
accordance with LDP Capability definition guidelines [RFC5561], that
is to be advertised to its peers by an mLDP speaker to announce its
capability to support MTR and the procedures specified in this
document. This capability MAY be sent either in an Initialization
message at the session establishment time, or in a Capability
message dynamically during the lifetime of a session (only if
"Dynamic Announcement" capability [RFC5561] has been successfully
negotiated with the peer).
The format of this capability is as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Multipoint MT Cap.(IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
Figure 1 : "Multipoint MT Capability" TLV Format
Where:
U- and F-bits: MUST be 1 and 0, respectively, as per Section 3 of
LDP Capabilities [RFC5561].
Multipoint MT: TLV type (IANA assigned).
Length: The length (in octets) of TLV. The value of this field
MUST be 1 as there is no Capability-specific data [RFC5561] that
follows in the TLV.
S-bit: MUST be 1 if used in LDP Initialization message. MAY be
set to 0 or 1 in dynamic Capability message to advertise or
withdraw the capability respectively.
An mLDP speaker that has successfully advertised and negotiated
"Multipoint MT" capability MUST support the following:
1. Topology-scoped mLDP FECs in LDP messages ( Section 4. )
2. Topology-scoped mLDP forwarding setup ( Section 7. )
6. MT Applicability on FEC-based features
6.1. Typed Wildcard MP FEC Elements
RFC5918 extends base LDP and defines Typed Wildcard FEC Element
framework [RFC5918]. Typed Wildcard FEC element can be used in any
LDP message to specify a wildcard operation/action for given type of
FEC.
The MT extensions proposed in document do not require any extension
in procedures for Typed Wildcard Prefix FEC element, and these
procedures apply as-is to Multipoint MT FEC wildcarding. The MT
extensions, though, allow use of "MT IP" or "MT IPv6" in the Address
Family field of the Typed Wildcard FEC element in order to use
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wildcard operations in the context of a given topology. The use of
MT-scoped address family also allows us to specify MT-ID in these
operations.
This document extends Typed Wildcard MP FEC element encoding for MT
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Typed Wcard (5)| Type = MP FEC | Len = 6 | AF = MT IP ..|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|... or MT IPv6 | Reserved | MT ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MT ID (contd.) |
+-+-+-+-+-+-+-+-+
Fig 6: "Typed Wildcard MP FEC Element" for MT
The proposed format allows an LSR to perform wildcard MP FEC
operations under the scope of a topology.
6.2. End-of-LIB
[RFC5919] specifies extensions and procedures for an LDP speaker to
signal its convergence for given FEC type towards a peer. The
procedures defined in [RFC5919] apply as-is to MT MP FEC element.
This means that an mLDP speaker MAY signal its mLDP convergence
using Typed Wildcard MP FEC element, and its MT mLDP convergence per
topology using MT Typed Wildcard MP FEC element (as defined in
earlier section).
7. Topology-Scoped Forwarding
Since the MTID is part of the mLDP FEC, there is no need to support
the concept of multiple topology tables in mLDP. Each MP LSP will be
unique due to the MTID being part of the FEC. There is also no need
to have specific Label Forwarding Tables per topology. Each MP LSP
will have its own unique local label in the LFT. In order to satisfy
the MTR in mLDP, the upstream LSR and downstream forwarding
interface procedures must be changed.
7.1. Upstream LSR selection
The procedures as described in draft-ietf-mpls-ldp-p2mp-15 section-
2.4.1.1 depend on the best path to reach the root. When the MTID is
signaled as part of the FEC, the MTID is used to select the topology
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that must to be used to find the best path to the root address.
Using the next-hop from this best path, a LDP peer is selected
following the procedures as defined in draft-ietf-mpls-ldp-p2mp-15.
7.2. Downstream forwarding interface
The procedures as described in draft-ietf-mpls-ldp-p2mp-15 section-
2.4.1.2 describe how a downstream forwarding interface is selected.
In these procedures any interface leading to the downstream LDP
neighbor can be considered as candidate forwarding interface. When
the MTID is part of the FEC, this is no longer true. An interface
must only be selected if it is part of the same topology that was
signaled in the mLDP FEC element. Besides this restriction, the
other procedures in draft-ietf-mpls-ldp-p2mp-15 section-2.4.1.2
apply.
8. Security Considerations
This extension to mLDP does not introduce any new security
considerations beyond that already apply to the base LDP
specification [RFC5036], base mLDP specification [RFC6388], and MPLS
security framework [RFC5920].
9. IANA Considerations
The document introduces following new protocol elements that require
IANA consideration and code point assignment:
o New LDP Capability TLV: "Multipoint MT Capability" TLV (requested
code point: 0x50F from LDP registry "TLV Type Name Space")
o New address families under IANA registry "Address Family
Numbers":
- MT IP: Multi-Topology IP version 4 (requested codepoint: 26)
- MT IPv6: Multi-Topology IP version 6 (requested codepoint: 27)
o New registry "LDP Multi-Topology (MT) ID Name Space" under "LDP
Parameter" namespace. The registry is defined as:
Range/Value Name
----------- ------------------------
0 Default Topology
1-4095 Unassigned
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4096-65534 Reserved (for future allocation)
65535 Wildcard Topology
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.
[RFC4915] P. Psenak, S. Mirtorabi, A. Roy, L. Nguyen, P. Pillay-
Esnault, "Multi-Topology Routing in OSPF", RFC 4915, June
2007.
[RFC5120] T. Przygienda, Z2 Sagl, N. Shen, N., "M-ISIS: Multi-
Topology Routing in IS-IS", RFC 5120, February 2008.
[MT-LDP] Q. Zhao, L. Fang, C. Zhou, L. Li, N. So, R. Torvi, "LDP
Extension for Multiple Topology Support", draft-zhao-mpls-
ldp-multi-topology-02, Work in progress, July 2011.
[RFC6388] I. Minei, I. Wijnand, K. Kompella, B., "LDP Extensions for
P2MP and MP2MP LSPs", RFC 6388, November 2011.
10.2. Informative References
[RFC5036] L. Andersson, I. Minei, B. Thomas, "LDP Specification",
RFC 5036, October 2007.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and
Le Roux, JL., "LDP Capabilities", RFC 5561, July 2009.
[RFC5919] R. Asati, P. Mohapatra, E. Chen, B. Thomas, "Signaling LDP
Label Advertisement Completion", RFC 5919, August 2010.
[RFC5918] Asati, R., Minei, I., and Thomas, B. "Label Distribution
Protocol Typed Wildcard FEC", RFC 5918, August 2010.
[RFC5920] L. Fang, L. et al., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
11. Acknowledgments
The authors would like to acknowledge Eric Rosen for his input on
this specification.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
IJsbrand Wijnand
Cisco Systems, Inc.
De kleetlaan 6a,
Diegem 1831 Belgium.
Email: ice@cisco.com
Kamran Raza
Cisco Systems, Inc.
2000 Innovation Drive,
Ottawa, Ontario K2K-3E8, Canada.
Email: skraza@cisco.com
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