Network Working Group R. Aggarwal
Internet Draft Juniper Networks
Expiration Date: September 2010
J. L. Le Roux
France Telecom
March 08, 2010
MPLS Upstream Label Assignment for RSVP-TE
draft-ietf-mpls-rsvp-upstream-05.txt
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Abstract
This document describes procedures for distributing upstream-assigned
labels for Resource Reservation Protocol - Traffic Engineering (RSVP-
TE). It also describes how these procedures can be used for avoiding
branch LSR traffic replication on a LAN for RSVP-TE point-to-
multipoint (P2MP)LSPs.
Table of Contents
1 Specification of requirements ......................... 3
2 Introduction .......................................... 3
3 RSVP-TE Upstream Label Assignment Capability .......... 3
4 Distributing Upstream-Assigned Labels in RSVP-TE ...... 4
4.1 Procedures ............................................ 5
5 RSVP-TE Tunnel Identifier Exchange .................... 5
6 RSVP-TE Point-to-Multipoint LSPs on a LAN ............. 7
7 IANA Considerations ................................... 8
8 Security Considerations ............................... 8
9 Acknowledgements ...................................... 9
10 References ............................................ 9
10.1 Normative References .................................. 9
10.2 Informative References ................................ 9
11 Author's Address ...................................... 10
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1. Specification of requirements
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].
2. Introduction
This document describes procedures for distributing upstream-assigned
labels [RFC5331] for Resource Reservation Protocol with Traffic
Engineering (RSVP-TE). These procedures follow the architecture for
MPLS Upstream Label Assignment described in [RFC5331].
This document describes extensions to RSVP-TE that a LSR can use to
advertise to its neighboring LSRs whether the LSR supports upstream
label assignment.
This document also describes extensions to RSVP-TE to distribute
upstream-assigned labels.
The usage of MPLS upstream label assignment using RSVP-TE for
avoiding branch LSR [RSVP-P2MP] traffic replication on a LAN for
RSVP-TE P2MP TE LSPs [RFC4875] is also described.
3. RSVP-TE Upstream Label Assignment Capability
According to [RFC5331], upstream-assigned label bindings MUST NOT be
used unless it is known that a downstream LSR supports them. This
implies that there MUST be a mechanism to enable a LSR to advertise
to its RSVP-TE neighbor LSR(s) its support of upstream-assigned
labels.
[RFC5063] defines a CAPABILITY object to be carried within Hello
messages, and used to indicate the set of capabilities supported by a
node. This object provides the ability to encode a set of capability
flags. This document defines a new flag, the U flag, to signal a
LSR's support of upstream label assignment to its RSVP-TE neighbors.
The format of a Capability object 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Class-Num(TBA)| C-Type (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |U|T|R|S|
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
T, R and S flags are defined in [RFC5063].
Upstream Label Assignement Capable (U): 1 bit When set this means
that the LSR is capable of both distributing upstream-assigned label
bindings and receiving upstream-assigned label bindings
Reserved bits MUST be set to zero on transmission and MUST be ignored
on receipt.
The usage of RSVP-TE Hello messages for exchanging upstream label
assignment capability implies that a LSR MAY exchange RSVP-TE Hellos
with a neighbor before sending/receiving any other RSVP-TE messages
to/from that neighbor.
4. Distributing Upstream-Assigned Labels in RSVP-TE
An optional RSVP-TE object, the UPSTREAM_ASSIGNED_LABEL object is
introduced to signal an upstream-assigned label. The Class-Num for
this object comes from the 0bbbbbbb space and is to be determined by
IANA.
UPSTREAM_ASSIGNED_LABEL C-Num = TBD
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label |
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The label can be encoded as in [RFC3209] when the C-Type is 1 or as a
Generalized Label [RFC3473] when the C-Type is 2 or 3.
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4.1. Procedures
A RSVP-TE LSR that assigns Upstream-Assigned Labels, distributes them
to the downstream LSRs by including them in RSVP-TE Path messages.
A RSVP-TE LSR MUST NOT distribute the UPSTREAM_ASSIGNED_LABEL Object
to a downstream LSR if the downstream LSR had not previously
advertised the CAPABILITY object with the U bit set in its RSVP-TE
Hello messages.
If a downstream RSVP-TE LSR receives a Path message that carries an
UPSTREAM_ASSIGNED_LABEL Object and the LSR does not support the
object C-Num/C-Type it will return an "Unknown Object C-Num/C-Type"
error. If the LSR does support the object, but is unable to process
the upstream-assigned label as described in [RFC5331] it SHOULD send
a PathErr with the error code "Routing problem" and the error value
"MPLS Upstream Assigned Label Processing Failure". If the LSR
successfully processes the Path message and the upstream-assigned
label it MUST send a Resv message upstream as per [RFC3209] but it
MUST NOT include the LABEL object with a downstream assigned label in
the Resv Message. This is because as described in [RFC5331] two LSRs
Ru and Rd for a LSP that is bound to FEC F, MUST use either
downstream-assigned label distribution or upstream-assigned label
distribution,for FEC F, but NOT both, for packets that are to be
transmitted on the LSP from Ru to Rd.
5. RSVP-TE Tunnel Identifier Exchange
As described in [RFC5331] an upstream LSR Ru MAY transmit a MPLS
packet, the top label of which (L) is upstream-assigned, to a
downstream LSR Rd, by encapsulating it in an IP or MPLS tunnel. In
this case the fact that L is upstream-assigned is determined by Rd by
the tunnel on which the packet is received. There must be a mechanism
for Ru to inform Rd that a particular tunnel from Ru to Rd will be
used by Ru for transmitting MPLS packets with upstream-assigned MPLS
labels.
When RSVP-TE is used for upstream label assignment, the IF_ID
RSVP_HOP object is used for signaling the Tunnel Identifier. If Ru
uses an IP or MPLS tunnel to transmit MPLS packets with upstream
assigned labels to Rd, Ru MUST include the IF_ID RSVP_HOP object
[RFC3473] in Path messages along with the UPSTREAM_ASSIGNED_LABEL
Object.
Four new TLVs are introduced in the IF_ID RSVP_HOP object [RFC3471]
to support RSVP-TE P2MP LSPs, LDP P2MP LSPs, IP Multicast Tunnels and
context labels. The TLV value acts as the tunnel identifier.
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1. RSVP-TE P2MP LSP TLV. Type = TBD. Value of the TLV is the RSVP-TE
P2MP Session Object and optionally the P2MP Sender Template Object
[RFC4875]. The TLV value identifies the RSVP-TE P2MP LSP. This
mechanism extends RSVP-TE P2P Hierarchy [LSP-HIER] to RSVP-TE P2MP
Hierarchy. It allows Ru to tunnel an "inner" RSVP-TE P2MP LSP, the
label for which is upstream assigned, over an "outer" RSVP-TE P2MP
LSP that has leaves <Rd1...Rdn>. The P2MP LSP IF_ID TLV allows Ru to
signal to <Rd1...Rdn> the binding of the inner P2MP LSP to the outer
P2MP LSP. The control plane signaling between Ru and <Rd1...Rdn> for
the inner P2MP LSP uses directed RSVP-TE signaling messages as in
[LSP-HIER].
2. LDP P2MP LSP TLV. Type = TBD. Value of the TLV is the LDP P2MP FEC
as defined in [MLDP]. The TLV value identifies the LDP P2MP LSP. It
allows Ru to tunnel an "inner" RSVP-TE P2MP LSP, the label for which
is upstream assigned, over an "outer" LDP P2MP LSP that has leaves
<Rd1...Rdn>. The P2MP LSP IF_ID TLV allows Ru to signal to
<Rd1...Rdn> the binding of the inner LDP P2MP LSP to the outer LDP-
P2MP LSP. The control plane signaling between Ru and <Rd1...Rdn> for
the inner P2MP LSP uses directed RSVP-TE signaling messages as in
[LSP-HIER].
2. IP Multicast Tunnel TLV. Type = TBD. In this case the TLV value is
a <Source Address, Multicast Group Address> tuple. Source Address is
the IP address of the root of the tunnel i.e. Ru, and Multicast Group
Address is the Multicast Group Address used by the tunnel.
3. MPLS Context Label TLV. Type = TBD. In this case the TLV value is
a <Source Address, MPLS Context Label> tuple. The Source Address
belongs to Ru and the MPLS Context Label is an upstream assigned
label, assigned by Ru. This allows Ru to tunnel an "inner" RSVP-TE
P2MP LSP, the label of which is upstream assigned, over an "outer"
MPLS LSP, where the outer LSP has the following property:
+ The label pushed by Ru for the outer MPLS LSP is an upstream
assigned context label, assigned by Ru. When <Rd1...Rdn> perform
a MPLS label lookup on this label a combination of this label and
the incoming interface MUST be sufficient for <Rd1...Rdn> to
uniquely determine Ru's context specific label space to lookup
the next label on the stack in. <Rd1...Rdn> MUST receive the data
sent by Ru with the context specific label assigned by Ru being
the top label on the label stack.
Currently the usage of the context label TLV is limited only to RSVP-
TE P2MP LSPs on a LAN as specified in the next section. The context
label TLV MUST NOT be used for any other purposes.
Note that when the outer P2MP LSP is signaled with RSVP-TE or MLDP
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the above procedures assume that Ru has a priori knowledge of all the
<Rd1, ... Rdn>. In the scenario where the outer P2MP LSP is signaled
using RSVP-TE, Ru can obtain this information from RSVP-TE. However,
in the scenario where the outer P2MP LSP is signaled using MLDP, MLDP
does not provide this information to Ru. In this scenario the
procedures by which Ru could acquire this information are outside the
scope of this document.
6. RSVP-TE Point-to-Multipoint LSPs on a LAN
This section describes one application of upstream label assignment
using RSVP-TE. Further applications are to be described in separate
documents.
[RFC4875] describes how to setup RSVP-TE P2MP LSPs. On a LAN the
solution described in [RFC4875] relies on "ingress replication". A
LSR on a LAN (say Il), that is a branch LSR for a P2MP LSP, (say Ru)
sends a separate copy of a packet that it receives on the P2MP LSP to
each of the downstream LSRs on the LAN (say <Rd1...Rdn> that are
adjacent to it in the P2MP LSP.
In order to increase efficiency of bandwidth utilization, it is
desirable for Ru to send a single copy of the packet for the P2MP LSP
on the LAN, when there are multiple downstream routers on the LAN
that are adjacent in that P2MP LSP. This requires that each of
<Rd1...Rdn> must be able to associate the label L, used by Ru to
transmit packets for the P2MP LSP on the LAN, with that P2MP LSP. It
is possible to achieve this using RSVP-TE upstream-assigned labels
with the following procedures. Assume that Ru and <Rd1...Rdn> support
upstream label assignment.
Ru sends a Path message for the P2MP LSP to each of <Rd1...Rdn> that
is adjacent on the P2MP LSP, with the same UPSTREAM_ASSIGNED_LABEL
object. This object carries an upstream assigned label, L. This
message also carries a MPLS Context Label TLV, as described in the
previous section, with the value of the MPLS label set to a value
assigned by Ru on inteface I1 as specified in [RFC5331]. <Rd1...Rdn>
"reserve" the upstream assigned label in the separate Upstream
Neighbor Label Space that they maintain for Ru [RFC5331].
Ru can then transmit a single packet for the P2MP LSP to <Rd1..Rdn>
with a top label L using procedures defined in [RFC5331] and
[RFC5332]. The MPLS packet transmitted by Ru contains as the top
label the context label assigned by Ru on the LAN interface, I1. The
bottom label is the upstream label assigned by Ru to the RSVP-TE P2MP
LSP. The top label is looked up in the context of the LAN interface,
I1, [RFC5331] by a downstream LSR on the LAN. This lookup enables the
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downstream LSR to determine the context specific label space to
lookup the inner label in.
If a subset of <Rd1...Rdn> do not support upstream label assignment
these procedures can still be used between Ru and the remaining
subset of <Rd1...Rdn>. Ingress replication and downstream label
assignment will continue to be used for LSRs that do not support
upstream label assignment.
7. IANA Considerations
This document defines a new U flag in the CAPABILITY object defined
by [RFC5063]. IANA is requested to assign a new bit to this flag from
the 32 bit flags field of the CAPABILITY object.
This document defines a new RSVP-TE object, the
UPSTREAM_ASSIGNED_LABEL object. The Class-Num for this object comes
from the 0bbbbbbb space and IANA is requested to assign this Class-
Num.
This document defines four new TLVs in the IF_ID RSVP_HOP object
[RFC3471]:
- RSVP-TE P2MP LSP TLV
- LDP P2MP LSP TLV
- IP Multicast Tunnel TLV
- MPLS Context Label TLV
IANA is requested to assign the type values of these TLVs.
8. Security Considerations
The security considerations discussed in RFC 5331 and RFC 5332 apply
to this document.
More detailed discussion of security issues that are relevant in the
context of MPLS and GMPLS, including security threats, related
defensive techniques, and the mechanisms for detection and reporting,
are discussed in "Security Framework for MPLS and GMPLS Networks
[MPLS-SEC].
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9. Acknowledgements
Thanks to Yakov Rekhter for his contribution. Thanks to Ina Minei and
Thomas Morin for their comments.
10. References
10.1. Normative References
[RFC3031] "MPLS Architecture", E. Rosen, A. Viswanathan, R. Callon,
RFC 3031.
[RFC5331] R. Aggarwal, Y. Rekhter, E. Rosen, "MPLS Upstream Label
Assignment and Context Specific Label Space", draft-ietf-mpls-
upstream-label-05.txt
[RFC5332] T. Eckert, E. Rosen, R. Aggarwal, Y. Rekhter, draft-ietf-
mpls-codepoint-08.txt
[RFC3209] Awduche et. al." "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels.", Bradner, March 1997
[RFC3473] Berger, L., Editor, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling - Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3471] Berger, L. Editor, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC 3471 January
2003.
[RFC5063] A. Satyanarayana et. al., "Extensions to GMPLS Resource
Reservation Protocol (RSVP) Graceful Restart", RFC5063
10.2. Informative References
[MVPN] E. Rosen, R. Aggarwal [Editors], "Multicast in BGP/MPLS VPNs",
draft-ietf-l3vpn-2547bis-mcast-06.txt
[RFC4875] R. Aggarwal, D. Papadimitriou, S. Yasukawa [Editors],
"Extensions to RSVP-TE for Point to Multipoint TE LSPs", RFC 4875
[MPLS-SEC] L. fang, ed, "Security Framework for MPLS and GMPLS
Networks", draft-ietf-mpls-mpls-and-gmpls-security-framework-07.txt
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11. Author's Address
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Phone: +1-408-936-2720
Email: rahul@juniper.net
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
France
E-mail: jeanlouis.leroux@orange-ftgroup.com
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