Internet DRAFT - draft-villamizar-mpls-tp-multipath-te-extn
draft-villamizar-mpls-tp-multipath-te-extn
MPLS C. Villamizar, Ed.
Internet-Draft Outer Cape Cod Network
Intended status: Standards Track Consulting
Expires: April 10, 2013 October 7, 2012
Multipath Extensions for MPLS Traffic Engineering
draft-villamizar-mpls-tp-multipath-te-extn-02
Abstract
Extensions to OSPF-TE, ISIS-TE, and RSVP-TE are defined in support of
carrying LSP with strict packet ordering requirements over multipath
and and carrying LSP with strict packet ordering requirements within
LSP without violating requirements to maintain packet ordering. LSP
with strict packet ordering requirements include MPLS-TP LSP.
OSPF-TE and ISIS-TE extensions defined here indicate node and link
capability regarding support for ordered aggregates of traffic,
multipath traffic distribution, and abilities to support multipath
load distribution differently per LSP.
RSVP-TE extensions either identifies an LSP as requiring strict
packet order, or identifies an LSP as carrying one or more LSP that
requires strict packet order further down in the label stack, or
identifies an LSP as having no restrictions on packet ordering except
the restriction to avoid reordering microflows. In addition an
extension indicates whether the first nibble of payload will reliably
indicate whether payload is IPv4, IPv6, or other type of payload,
most notably pseudowire using a pseudowire control word.
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 April 10, 2013.
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Copyright Notice
Copyright (c) 2012 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
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Architecture Summary . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5
1.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 6
2.1. Multipath Node Capability sub-TLV . . . . . . . . . . . . 6
2.2. Multipath Link Capability TLV . . . . . . . . . . . . . . 9
2.3. LSP Multipath Attributes TLV . . . . . . . . . . . . . . . 9
3. Protocol Mechanisms . . . . . . . . . . . . . . . . . . . . . 12
3.1. OSPF-TE and ISIS-TE Advertisement . . . . . . . . . . . . 12
3.1.1. Node Capability Advertisement . . . . . . . . . . . . 12
3.1.2. Link Capability Advertisement . . . . . . . . . . . . 12
3.1.3. Setting Max Depth and IP Depth . . . . . . . . . . . . 12
3.1.4. Advertising Multipath as Link Bundling . . . . . . . . 13
3.1.5. Hierarchical LSP Link Advertisement . . . . . . . . . 13
3.1.6. Advertisement of Legacy Multipath . . . . . . . . . . 14
3.2. RSVP-TE LSP Attributes . . . . . . . . . . . . . . . . . . 15
3.2.1. LSP Contained Ordered Aggregates Flags . . . . . . . . 15
3.2.2. LSP Attributes for Ordered Aggregates . . . . . . . . 17
3.2.3. Attributes for LSP without Packet Ordering . . . . . . 17
3.3. Path Computation Constraints . . . . . . . . . . . . . . . 20
3.3.1. Link Multipath Capabilities and Path Computation . . . 20
3.3.1.1. Path Computation with Ordering Constraints . . . . 20
3.3.1.2. Path Computation with No Ordering Constraint . . . 21
3.3.1.3. Path Computation for MPLS containing MPLS-TP . . . 21
3.3.2. Link IP Capabilities and Path Computation . . . . . . 21
3.3.2.1. LSP without Packet Ordering Requirements . . . . . 22
3.3.2.2. LSP with Ordering Requirements . . . . . . . . . . 22
3.3.3. Link Depth Limitations and Path Computation . . . . . 23
4. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 24
4.1. Legacy Multipath Behavior . . . . . . . . . . . . . . . . 24
4.2. Networks without Multipath Extensions . . . . . . . . . . 24
4.2.1. Netowrks with MP Capability on all Multipath . . . . . 24
4.2.2. Netowrks with OA Capability on all Multipath . . . . . 26
4.2.3. Legacy Netowrks with Mixed MP and OA Links . . . . . . 26
4.3. Transition to Multipath Extension Support . . . . . . . . 27
4.3.1. Simple Transitions . . . . . . . . . . . . . . . . . . 27
4.3.2. More Challenging Transitions . . . . . . . . . . . . . 27
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
6. Security Considerations . . . . . . . . . . . . . . . . . . . 28
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1. Normative References . . . . . . . . . . . . . . . . . . . 28
7.2. Informative References . . . . . . . . . . . . . . . . . . 29
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
Today the requirement to handle large aggregations of traffic, can be
handled by a number of techniques which we will collectively call
multipath. Multipath is very similar to composite link as defined in
[ITU-T.G.800], except multipath specifically excludes inverse
multiplexing. Some types of LSP, including but potentially not
limited to MPLS-TP LSP, require strict packet ordering.
A means to support a MPLS-TP client layer over a MPLS server layer
using MPLS Entropy Label is defined in
[I-D.villamizar-mpls-tp-multipath]. It is noted in
[I-D.villamizar-mpls-tp-multipath] that absent some protocol
extensions, some limitations must be accepted.
This document defines protocol extensions which better supports using
MPLS with multipath as a server layer for MPLS-TP, or to carry
MPLS-TP directly over a network which makes use of multipath.
Extensions are also applicable to MPLS when used in the presense of
very large microflows or very large LSP which cannot be load split as
a result of using MPLS Entropy Label [I-D.ietf-mpls-entropy-label].
1.1. Architecture Summary
Advertisements in a link state routing protocol, such as OSPF or
ISIS, support a topology map known as a link state database (LSDB).
When traffic engineering information is included in the LSDB the
topology map is known as a TE-LSDB or traffic engineering database
(TED).
A common MPLS LSP path computation is known as a constrained shortest
path first computation (CSPF) (see [RFC3945]). Other algorithms may
be used for path computation. Constraint-based routing was first
introduced in [RFC2702]).
OSPF-TE or ISIS-TE extensions are defined in Section 2.1 and
Section 2.2. OSPF-TE or ISIS-TE advertisements serve to populate the
TE-LSDB and provide the basis for constraint-based routing path
computation. Section 3.1 describes the use of OSPF-TE or ISIS-TE
multipath extensions in routing advertisements.
RSVP-TE extensions are defined in Section 2.3. Section 3.2 describes
the use of RSVP-TE extensions in setting up LSP including signaling
constraints on LSP which contain other LSP which specify RSVP-TE
extensions.
Section 3.3 describes the constraints on LSP path computation imposed
by the advertised ordered aggregate and multipath capabilities of
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links. Section 3.3.2 describes the constraints on LSP path
computation imposed by link advertisements regarding use of IP
headers in multipath traffic distribution. Section 3.3.3 describes
the impact of label stack depth limitations.
1.2. 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 RFC 2119 [RFC2119].
1.3. Definitions
Please refer to [I-D.villamizar-mpls-tp-multipath].
Ordered Aggregate (OA)
An ordered aggregate (OA) requires that packets be delivered in
the order in which they were received. Please refer to [RFC3260].
Microflow
A microflow is a single instance of an application-to- application
flow. Please refer to [RFC2475]. Reordering packets within a
microflow can cause service disruption. Please refer to
[RFC2991].
Multipath Traffic Distribution
Multipath traffic distribution refers to the mechanism which
distributes traffic among a set of component links or component
lower layer paths which together comprise a multipath. No
assumptions are made about the algorithms used in multipath
traffic distribution. This document only discusses constraints of
the type of information which can be used as the basis for
multipath traffic distribution in specific circumstances.
The phrase "strict packet ordering requirements" refers to the
requirement to deliver all packet in the order that they were
received. The absence of strict packet ordering requirements does
not imply total absence of packet ordering requirements. The
requirement to avoid reordering traffic within any given microflow,
as described in [RFC2991] applies to all traffic aggregates including
all MPLS LSP.
The abbreviations ELI and EL are Entropy Label Indicator and Entropy
Label, as defined in [I-D.ietf-mpls-entropy-label].
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2. Protocol Extensions
This section defined protocol extensions to OSPF-TE, ISIS-TE, and
RSVP-TE. Use of these extensions is described in Section 3 and
Section 4.
Two capability sub-TLV are added to two TLV that are used in both
OSPF-TE and ISIS-TE. The Multipath Node Capability sub-TLV is added
to the Node Attribute TLV ( see Section 2.1). The Multipath Link
Capability TLV is added to the Interface_ID (see Section 2.2).
One TLV is added to the LSP_ATTRIBUTES object defined in [RFC5420].
2.1. Multipath Node Capability sub-TLV
The Node Attribute TLV is defined in [RFC5786]. A new sub-TLV, the
Multipath Node Capability sub-TLV, is defined for inclusion in the
Node Attribute TLV.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Max Depth | IP Depth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Largest Supportable Microflow |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Multipath Capability Sub-TLV
The fields in the Multipath Capability sub-TLV are defined as
follows.
Type
The Type field is assigned a value of IANA-TBD-1. The Type field
is a two octet value.
Length
The Length field indicates the length of the sub-TLV in octets,
excluding the Type and Length fields. The Length field is a two
octet value.
Flags
The Flags field is a two octet (16 bit) value. The following
single bit fields are assigned within this value, starting at the
most significant bit, which is the bit transmitted first.
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0x8000 Ordered Aggregate Enabled
Setting the Ordered Aggregate Enabled bit indicates that an LSP
can be carried as an Ordered Aggregate Enabled on one or more
links.
0x4000 Multipath Enabled
Setting the Multipath Enabled bit indicates that an LSP can be
spread across component links at one or more multipath links.
0x2000 IPv4 Enabled Multipath
Setting the IPv4 Enabled Multipath bit indicates that the IPv4
header information can be used in multipath load balance. The
Multipath Enabled bit must be set if the IPv4 Enabled Multipath
bit is set.
0x1000 IPv6 Enabled Multipath
Setting the IP bit indicates that the IPv6 header information
can be used in multipath load balance. The Multipath Enabled
bit must be set if the IPv6 Enabled Multipath bit is set.
0x0800 UDP/IPv4 Multipath
Setting the UDP/IPv4 Multipath bit indicates that the UDP port
numbers carried in UDP over IPv4 can be used in multipath load
balance. The IPv4 Enabled Multipath bit must be set if UDP/
IPv4 Multipath is set. If the IPv4 Enabled Multipath bit is
set and the UDP/IPv4 Multipath bit is clear, then only source
and destination IP addresses are used.
0x0400 UDP/IPv6 Multipath
Setting the UDP/IPv6 Multipath bit indicates that the UDP port
numbers carried in UDP over IPv6 can be used in multipath load
balance. The IPv6 Enabled Multipath bit must be set if UDP/
IPv6 Multipath is set. The IPv6 Enabled Multipath bit must be
set if UDP/IPv6 Multipath is set. If the IPv6 Enabled
Multipath bit is set and the UDP/IPv6 Multipath bit is clear,
then only source and destination IP addresses are used.
0x0200 TCP/IPv4 Multipath
Setting the TCP/IPv4 Multipath bit indicates that the TCP port
numbers carried in TCP over IPv4 can be used in multipath load
balance. The IPv4 Enabled Multipath bit must be set if TCP/
IPv4 Multipath is set. If the IPv4 Enabled Multipath bit is
set and the TCP/IPv4 Multipath bit is clear, then only source
and destination IP addresses are used.
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0x0100 TCP/IPv6 Multipath
Setting the TCP/IPv6 Multipath bit indicates that the TCP port
numbers carried in TCP over IPv6 can be used in multipath load
balance. The IPv6 Enabled Multipath bit must be set if TCP/
IPv6 Multipath is set. The IPv6 Enabled Multipath bit must be
set if TCP/IPv6 Multipath is set. If the IPv6 Enabled
Multipath bit is set and the TCP/IPv6 Multipath bit is clear,
then only source and destination IP addresses are used.
0x0080 Default to Multipath
Setting the Default to Multipath bit indicates that for an LSP
which does not signal a desired behavior the traffic for that
LSP will be spread across component links at one or more
multipath links. If the Default to Multipath bit is not set,
then an LSP which does not signal otherwise will be treated as
an ordered aggregate.
0x0040 Default to IP/MPLS Multipath
Setting the Default to IP/MPLS Multipath indicates that for an
LSP which does not signal a desired behavior, the IP header
information will be used in the multipath load distribution.
If the Default to IP/MPLS Multipath is clear it indicates that
the the IP header information will not be used by default.
0x0020 Entropy Label Multipath
Setting the Entropy Label Multipath bit indicates that when
multipath is enabled for a given LSP, if an Entropy Label
Indicator (ELI) is found in the label stack, information below
the Entropy Label (EL) will not be used in multipath load
distribution.
0x0010 IP Optional Multipath
Setting the IP Optional Multipath bit indicates that when
multipath is enabled for a given LSP, whether the IP header
information is used in the multipath load distribution can be
set on a per LSP basis.
The remaining bits in the Flags field are reserved.
Max Depth
The Max Depth field is a one octet field indicating the maximum
label stack depth beyond which the multipath load distribution
cannot make use of further label stack entries.
IP Depth
The IP Depth field is a one octet field indicating the maximum
label stack depth beyond which the multipath load distribution
cannot make use of IP information.
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Largest Supportable Microflow
The Largest Supportable Microflow field is a IEEE 32 bit floating
point value expressing in bytes/second. Any microflow which
exceeds this capacity may experience either packet loss, or out-
of-order delivery, or both.
The reserved bits in the Flags field MUST be set to zero and MUST be
ignored unless implementing an extension which redefines one or more
of the reserved bits. Any further extension which redefines one or
more reserved Flags bit should maintain backwards compatibility with
prior implementations.
2.2. Multipath Link Capability TLV
The Interface_ID is defined in [RFC3471]. The Interface_ID is
updated in [RFC4201] to support a form of multipath known as Link
Bundling.
A new TLV, the Multipath Link Capability TLV, is defined here. The
Multipath Link Capability TLV is optionally included in the
Interface_ID. The format of the Multipath Link Capability TLV is
identical to the Multipath Node Capability sub-TLV defined in
Section 2.1, with one exception. In the Multipath Link Capability
TLV the Type field value is IANA-TBD-2.
If a Multipath Link Capability TLV is advertised for any link, then a
Multipath Node Capability sub-TLV MUST be advertised for the node.
2.3. LSP Multipath Attributes TLV
The LSP_ATTRIBUTES object is defined in [RFC5420]. A new LSP
Multipath Attributes TLV is defined for the LSP_ATTRIBUTES object.
The TLV Type is IANA_TBD_3. The format is described below.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | OA Depth | LSP Min Depth | LSP IP Depth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Largest Microflow Capacities |
| (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: LSP Multipath Attributes TLV
The fields in the LSP Multipath Attributes TLV are defined as
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follows.
Type
The Type field is assigned a value of IANA-TBD-3. The Type field
is a two octet value.
Length
The Length field indicates the length of the sub-TLV in octets,
excluding the Type and Length fields. The Length field is a two
octet value.
Flags
The Flags field is a one octet (8 bit) value. The following
single bit fields are assigned within this value, starting at the
most significant bit, which is the bit transmitted first.
0x80 IP Multipath Allowed
Setting the IP Multipath Allowed bit indicates that it is safe
to enable the use of a potential IP payload in the multipath
traffic distribution.
0x40 May Contain IPv4
Setting the May Contain IPv4 bit indicates that IPv4 traffic
may be contained within this LSP.
0x20 May Contain IPv6
Setting the May Contain IPv6 bit indicates that IPv6 traffic
may be contained within this LSP.
0x02 Entropy Label Required
Setting the Entropy Label Used bit indicates that midpoint LSR
MUST support ELI and EL in order to not violate packet ordering
constraints of the LSP or of contained LSP.
0x01 Entropy Label Used
Setting the Entropy Label Used bit indicates that an ELI and EL
is present in some or all label stack entries within this LSP.
The remaining bits in the Flags field are reserved.
OA Depth
The OA Depth field is set as follows
0 An OA Depth value of zero indicates that no ordered aggregates
are carried within the LSP, except those which are protected
from out of order delivery using Entropy Label.
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1 An OA Depth value of one indicates that the LSP is an ordered
aggregate of traffic (the LSP requires strict ordering of
packets) and has protected packet ordering using ELI and EL.
>1 An OA Depth value greater than one indicates that the LSP does
not have strict packet ordering requirements but contains
ordered aggregates at the label stack depth indicated or deeper
and that the ordered aggregates are not protected using ELI and
EL.
LSP Min Depth
The LSP Min Depth field indicates a minimal acceptable number of
label used in multipath traffic distribution for the stated
Largest Microflow Capacities field to be valid. If the LSP Min
Depth field is set to zero this value is unknown. See
Section 3.3.3.
LSP IP Depth
The LSP IP Depth field indicates a minimal label stack depth where
using an IP header is necessary for the stated Largest Microflow
Capacities field to be valid. If the LSP IP Depth field is set to
zero this value is unknown. See Section 3.3.3.
Largest Microflow Capacities
The Largest Microflow Capacities field contains zero, one, two, or
three IEEE 32 bit floating point values. Each value is a capacity
expressed in bytes per second.
Largest LSE Microflow
The first value, the Largest LSE Microflow, is the capacity of
the largest microflow if only the label stack entries are used
in multipath traffic distribution. If a Largest LSE Microflow
is not included, the LSP bandwidth request MUST be used.
Largest IP Microflow
The second value, the Largest IP Microflow, if present, is the
capacity of the largest microflow if the label stack entries
and any potential IP source and destination address are used in
multipath traffic distribution. If the Largest IP Microflow is
not included, the value of the Largest LSE Microflow MUST be
used.
Largest L4 Microflow
The third, the Largest L4 Microflow, if present, is the
capacity of the largest microflow if the label stack entries
and any potential IP addresses and TCP or UDP port numbers are
used in multipath traffic distribution. If a Largest L4
Microflow is not included, the value of the Largest IP
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Microflow MUST be used.
3. Protocol Mechanisms
3.1. OSPF-TE and ISIS-TE Advertisement
Every compliant node MUST advertise exactly one Multipath Node
Capability sub-TLV and MAY advertise zero of more Multipath Link
Capability sub-TLV as needed.
Procedures for accommodating legacy forwarding capabilities and non-
compliant nodes are discussed in Section 4.
3.1.1. Node Capability Advertisement
Every LSR which is adjacent to one or more multipath link MUST
advertise a Multipath Node Capability sub-TLV (see Section 2.1). The
capabilities advertised for the node SHOULD reflect the capabilities
of the majority of multipath links adjacent to the node.
Every LSR which is not adjacent to any multipath links MUST advertise
a Multipath Node Capability sub-TLV with both the Ordered Aggregate
Enabled bit in Flags set and all other Flags bits clear. Both Max
Depth and IP Depth can be set to zero. This advertisement identifies
the LSR as one which is conformant but has no multipath links,
allowing it to be distinguished from a non-conformant LSR with LAG or
other multipath which may have to be avoided when determining a path
for some LSP.
3.1.2. Link Capability Advertisement
For all of the links whose capability does not exactly match the
Multipath Node Capability sub-TLV advertised by that same LSR, the
LSR MUST advertise a Multipath Link Capability sub-TLV (see
Section 2.2).
For all of the links whose capability does exactly match the
Multipath Node Capability sub-TLV advertised by that same LSR, the
LSR SHOULD NOT advertise a Multipath Link Capability sub-TLV (see
Section 2.2). In this case the Multipath Link Capability TLV is
redundant, but harmless.
3.1.3. Setting Max Depth and IP Depth
The Max Depth and IP Depth field are intended to capture
architectural limits. Most forwarding hardware will only use a
limited number of label entries in the multipath traffic
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distribution. This limit is reflected in the Max Depth field. Most
forwarding hardware will limit the number of label entries that it
will look past before looking for an IP header to be used in the
multipath traffic distribution. This limit is reflected in the IP
Depth field.
3.1.4. Advertising Multipath as Link Bundling
All multipath links and FA for PSC LSP which traverse multipath links
MAY be advertised as Link Bundles as defined in [RFC4201]. The
settings of the Ordered Aggregate Enabled and Multipath Enabled
fields indicate key capabilities of the multipath. Advertising the
multipath as a link bundle can provide additional information, such
as the capability to place LSP on individual components.
If the Multipath Enabled bit is set in the Multipath Link Capability
TLV Flags, then the Maximum LSP Bandwidth in the Interface
Identification TLV can be set in one of two ways.
1. If the desired behavior for legacy LSR acting as ingress is to
limit LSP to the capacity of a single component link, then
Maximum LSP Bandwidth SHOULD be set as specified in [RFC4201].
2. If the desired behavior for legacy LSR acting as ingress is to
allow LSP to exceed the capacity of a single component link, then
Maximum LSP Bandwidth MAY be set to a higher value, up to the
value of Maximum Reservable Bandwidth. This would normally be
done if the legacy LSR were known to be carrying traffic which is
easily load split, such as typical Internet traffic.
LSR acting as ingress SHOULD ignore the Maximum LSP Bandwidth and MAY
set up LSP with capacity up to the Maximum Reservable Bandwidth as
long as microflows within the LSP will not exceed the Largest
Supportable Microflow capacity.
3.1.5. Hierarchical LSP Link Advertisement
A PSC LSP, as defined in [RFC4206] and updated in [RFC6107], may
carry other LSP. When signaling a PSC LSP expected characteristics
of the contained traffic must be estimated. The FA advertised for
the PSC LSP MUST reflect the broadest set of requirements the PSC LSP
can carry. If the setup of an additional reservation would exceeded
current capacity, a PSC LSP may be resignaled using make-before-break
semantics ([RFC3209].
For example, if it is expected that a PSC LSP will carry MPLS-TP LSP
or other LSP with strict packet reordering requirements at some label
depth, the minimum label stack depth at which an LSP with strict
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packet reordering requirements can be carried must be signaled in the
OA Depth field of the LSP Multipath Attributes TLV (see Section 2.3.
When the Forwarding Adjacency (FA) is advertised, the advertised Max
Depth and IP Depth MUST be one less that the minimum of the Max Depth
and IP Depth of any link that the PSC LSP traverses. The Max Depth
and IP Depth are considered independently of each other. The
reduction by one takes into account the PSC label. The Flags
advertised for the FA MUST reflect the capabilities of the links
along the path.
3.1.6. Advertisement of Legacy Multipath
An Ethernet LAG with no support for Entropy Label MUST have the
Ordered Aggregate Enabled bit cleared and the Multipath Enabled bit
set in the Multipath Link Capability TLV Flags. This indicates that
a MPLS-TP compliant server layer cannot be supported and that LSP
larger than the component links (LAG members) can be supported.
A Link Bundle that does not support the all-ones component defined in
[RFC4201] MUST have the Ordered Aggregate Enabled bit set and the
Multipath Enabled bit cleared in the Multipath Link Capability TLV
Flags. This indicates that a MPLS-TP compliant server layer can be
supported and that LSP larger than the component links cannot be
supported.
A link bundle that can support either the pinning of a LSP to a
single component link or the spreading of traffic across multiple
component links MUST have the Ordered Aggregate Enabled bit set and
the Multipath Enabled bit set in the Multipath Link Capability TLV
Flags. This indicates that a MPLS-TP compliant server layer can be
supported and that LSP larger than the component links can also be
supported.
Any form of multipath that supports Entropy Label MUST have the
Ordered Aggregate Enabled bit set and the Multipath Enabled bit set
and the Entropy Label Multipath bit set in the Multipath Link
Capability TLV Flags. Any form of multipath that does not supports
Entropy Label MUST have the Entropy Label Multipath bit cleared in
the Multipath Link Capability TLV Flags.
The remaining bits in the Multipath Link Capability TLV Flags MUST be
set according to the capability and configuration of the multipath or
LSP.
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3.2. RSVP-TE LSP Attributes
All LSR SHOULD advertise a LSP Multipath Attributes TLV with the
RSVP-TE signaling for each LSP for which it is serving as ingress.
If any legacy LSR remain in the network, it is easier to assign an
acceptable default treatment for LSP signaled by those legacy LSR if
the conforming LSR always send a LSP Multipath Attributes TLV.
There are two general cases, an LSP requires strict ordering of
packets, or it doesn't. In the latter case the LSP may contain other
LSP that require strict ordering and those must be protected from
reordering using an Entropy Label as described in
[I-D.villamizar-mpls-tp-multipath]. These two cases are briefly
described below.
Ordered Aggregates
LSP with strict packet order requirements MUST set the OA Depth
field to one to indicate that the LSP MUST be treated as ordered
aggregate. See Section 3.2.2.
LSP without Packet Ordering
LSP which do not have strict packet order requirements MUST only
carry LSP whose requirements are reflected in the containing LSP
Multipath Attributes TLV. See Section 3.2.3.
If an attempt is made to signal a contained LSP whose Ordered
Aggregate Attributes TLV and LSP Multipath Attributes TLV cannot be
supported by the containing (PSC) LSP, one of the two following
actions MUST be taken.
1. The containing (PSC) LSP MAY be resignaled with appropriate TLVs
to carry the new contained LSP using make-before-break semantics,
then continue to forward the contained LSP PATH message if the
containing (PSC) LSP is successfully updated.
2. The LSR MAY reject the contained LSP signaling by sending a
PathErr message.
3.2.1. LSP Contained Ordered Aggregates Flags
The Flags field in the LSP Multipath Attributes TLV MUST be set as
follows.
1. If the LSP may directly contain IPv4 traffic, then the May
Contain IPv4 bit in the Flags field MUST be set.
2. If the LSP may directly contain IPv6 traffic, then the May
Contain IPv6 bit in the Flags field MUST be set.
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3. If the LSP contains an LSP which has the May Contain IPv4 bit in
the Flags field then the May Contain IPv4 bit in the Flags field
MUST be set in the containing LSP.
4. If the LSP contains an LSP which has the May Contain IPv6 bit in
the Flags field then the May Contain IPv6 bit in the Flags field
MUST be set in the containing LSP.
5. If the LSP may contain pseudowires that do not use a pseudowire
control word [RFC4385], and may contain IPv4 or IPv6 traffic,
then the IP Multipath Allowed bit in the Flags field MUST be
cleared.
6. If the LSP is known to contain no pseudowires that do not use a
pseudowire control word, then the IP Multipath Allowed bit in the
Flags field SHOULD be set unless disallowed due to a contained
LSP.
7. If an Entropy Label is added below the LSP label, then the
Entropy Label Used bit MUST be set.
8. If the LSP contains any LSP with the IP Multipath Allowed bit in
the Flags field clear, then the IP Multipath Allowed bit in the
Flags field MUST be clear.
If the LSP does not contain other LSP, it may contain IP traffic
and/or pseudowire that terminate on that LSR. If the LSP does not
contain other LSP. The LER will know whether the LSP is used in an
IP LER capacity. The LER will also know whether it terminates any
pseudowire for a given LSP. The LER will also know if it is using
Entropy Label for a given LSP and if it requires strict packet
ordering for a given LSP. Therefore, when a LSP does not contain
other LSP, then it is possible to accurately set the Flags field in
the LSP Multipath Attributes TLV, as well the OA Depth, and LSP IP
Depth fields.
If an LSP contains other LSP, and all of the contained include a LSP
Multipath Attributes TLV, then it is still possible to accurately set
the Flags field in the LSP Multipath Attributes TLV, as well the OA
Depth, and LSP IP Depth fields. It is only when LSP contains other
LSP that do not have a LSP Multipath Attributes TLV where default
behavior has to be configured based on assumptions about LSP
originated by the legacy LSR where there is a potential for those
configured assumptions to be inaccurate.
See Section 4 for guidelines for handling LSP which contain LSP that
do not have a LSP Multipath Attributes TLV. The most conservative
approach in this case is to clear the IP Multipath Allowed bit and
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set the May Contain IPv4 bit and the May Contain IPv6 bit, however
this may not always be necessary.
3.2.2. LSP Attributes for Ordered Aggregates
An LSP with strict packet order requirements MUST always include a
LSP Multipath Attributes TLV.
Most of the Flags in the LSP Multipath Attributes TLV can be set as
described in Section 3.2.1. There are two cases which affect the
setting of the remaining Flags bits.
Entropy Label not used
If an Entropy Label is not used, then the Entropy Label Used bit,
the Entropy Label Required bit, and the IP Multipath Allowed bit
MUST be cleared.
Entropy Label is used If an Entropy Label is used, then the Entropy
Label Used bit, and the Entropy Label Required bit, and the IP
Multipath Allowed bit MUST be set.
The OA Depth field MUST be set to one. The Min Depth MUST be set to
one. The LSP IP Depth SHOULD be set to zero. The Largest Microflow
Capacities field SHOULD be empty. The entire LSP is one microflow.
The Largest Microflow Capacities field MAY contain one entry if there
is some reason to do so, such as an LSP which may peak at capacity
higher than the bandwidth reserved for the LSP. The Largest
Microflow Capacities for an LSP SHOULD be configurable independently
of the LSP bandwidth reservation.
3.2.3. Attributes for LSP without Packet Ordering
If an LSP does not have strict packet order constraints, then the
LSR_ATTRIBUTE object SHOULD always include a LSP Multipath Attributes
TLV.
Most of the Flags in the LSP Multipath Attributes TLV can be set as
described in Section 3.2.1. There are two cases which affect the
setting of the remaining Flags bits, the OA Depth field, the LSP Min
Depth, and the LSP IP Depth field.
Entropy Label not used
* The OA Depth MUST be either set to zero or set to a configured
value that is greater than one, or set based on the contained
LSP.
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* If the OA Depth is set to a configured value, then any setup
attempt for a contained LSP with a depth greater than or equal
to that value SHOULD be rejected and a PathErr message sent.
Otherwise, if a setup attempt for a contained LSP with a depth
greater that the current value included in the containing LSP
OA Depth field, then the containing LSP MUST be rerouted with a
OA Depth field value greater than any of the contained OA Depth
field values.
* The Entropy Label Used bit MUST be set if any contained LSP has
the Entropy Label Used bit set.
* The Entropy Label Required bit MUST be set if any contained LSP
has the Entropy Label Required bit set.
Entropy Label is used
* The OA Depth MUST be set to zero.
* The Entropy Label Used bit MUST be set.
* The Entropy Label Required bit MUST be set if any contained LSP
has the Entropy Label Required bit set.
* The Entropy Label Required bit MUST be set if any contained LSP
has the OA Depth field set to a non-zero value.
* The Entropy Label Required bit SHOULD be clear if there are no
contained LSP has the OA Depth field set to a non-zero value
and no contained LSP with the Entropy Label Required bit set.
In this case the Entropy Label Required bit MAY be set by
configuration, generally in anticipation of needing it in the
future to carry other LSP.
* LSP Min Depth field MUST be set to three if the Entropy Label
Required bit is set.
* If the Entropy Label Required bit is not set, then the LSP Min
Depth field and LSP IP Depth field SHOULD be set to three if
there are no contained LSP. The LSP Min Depth field and LSP IP
Depth MAY be configured to a minimum value greater than three,
generally in anticipation of needing it in the future to carry
other LSP.
* If the Entropy Label Required bit is not set, and there are
contained LSP, then the LSP Min Depth field MUST be set to a
value greater than three.
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* If the Entropy Label Required bit is not set, the LSP Min Depth
field MUST be set to a value that is at least the sum of three
plus the LSP Min Depth field in any contained LSP.
* If the Entropy Label Required bit is not set, and either the
May Contain IPv4 bit or the May Contain IPv6 bit is set, then
the LSP IP Depth field MUST be set to a value of one or
greater.
* If the Entropy Label Required bit is not set, and any contained
LSP has the May Contain IPv4 bit or the May Contain IPv6 bit is
set, then the LSP IP Depth field MUST be set to a value of two
or greater.
* If the Entropy Label Required bit is not set, and any contained
LSP has the LSP IP Depth field set to a value greater than one,
then the LSP IP Depth field MUST be set to a value greater than
the highest LSP IP Depth value set in any contained LSP.
The values of the LSP Min Depth field and the LSP IP Depth field MAY
be constrained to upper limits by configuration. If an attempt to
setup a contained LSP would result in exceeding one of these limits,
then the LSR SHOULD reject the signaling attempt and send a PathErr
message.
If Entropy Label is not used on the signaled LSP and there are no
contained LSP, then the Largest LSE Microflow in the Largest
Microflow Capacities field MUST be set to the requested bandwidth of
the LSP. The optional Largest IP Microflow and Largest L4 Microflow
SHOULD be included and MAY be set to configured minimum values.
If Entropy Label is not used on the signaled LSP an LSP that does not
have strict packet order constraints contains other LSP, then the LSP
Multipath Attributes TLV advertised by the set of contained LSP MUST
be used to set the LSP Multipath Attributes TLV Largest Microflow
Capacities values for LSP Multipath Attributes TLV. The value of
Largest LSE Microflow, Largest IP Microflow, and Largest L4 Microflow
in the LSP Multipath Attributes TLV of the containing LSP cannot be
less than the maximum effective value of the same parameter for any
contained LSP Multipath Attributes TLV.
If Entropy Label is used on the signaled LSP then the Largest LSE
Microflow field is set according to the largest microflow that can
result from computing the Entropy Label. This value is the greatest
of a set of sources of entropy. A configured value MAY be used for
IP, or it MAY be assumed that the largest interface carrying IP could
carry a single microflow. For contained LSP which have the Entropy
Label Used bit clear, the value in the Largest IP Microflow can be
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used if the IP Multipath Allowed bit is set for that LSP and the LSR
can make use of the IP information in the label stack. For contained
LSP which have the Entropy Label Used bit set, the Largest LSE
Microflow value already reflects any prior hashing of IP fields.
If the Entropy Label Required bit is set and the LSP being set up is
using Entropy Label, then the Largest IP Microflow and Largest L4
Microflow SHOULD be omitted. All midpoint LSR SHOULD not look for
entropy beyond the Entropy Label.
If the LSP being set up is not using Entropy Label, then the Largest
IP Microflow and Largest L4 Microflow SHOULD be included unless the
Entropy Label Used bit is set for every contained LSP. The Largest
IP Microflow and Largest L4 Microflow SHOULD be omitted if hashing on
the IP addresses or IP addresses and ports would yield no greater
entropy than hashing on the label stack alone.
3.3. Path Computation Constraints
The RSVP-TE extensions provides a set of requirements to be met by
the links which the LSP is to traverse. This set of requirements
also serves as the basis for path computation constraints and for
admission control constraints.
3.3.1. Link Multipath Capabilities and Path Computation
Three cases are considered. An LSP may have strict ordering
constraints. An MPLS-TP LSP is an example of an LSP with strict
ordering constraints. This first type of LSP is covered in
Section 3.3.1.1. An LSP may have no ordering constraints at all
other than the constraint that microflows cannot be reordered. This
second case is covered in Section 3.3.1.2. The remaining case is
where an LSP has no ordering constraints but carries traffic for
other LSP which do have ordering constraints. This third case is
covered in Section 3.3.1.3.
3.3.1.1. Path Computation with Ordering Constraints
For an MPLS-TP LSP or other LSP with a strict packet ordering
constraint, any link or FA for which the Ordered Aggregate Enabled
bit and Entropy Label Multipath are both clear MUST be excluded from
the path computation. If the Default to Multipath bit is set on a
link, then setting the OA Depth field to one will override that
default.
Link with the Ordered Aggregate Enabled bit clear and the Entropy
Label Multipath bit set MAY be included in the path computation if
the LSR is capable of encapsulating an LSP with a strict packet
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ordering constraint with a fixed Entropy Label. If the LSR is not
capable of adding an ELI and EL, then these links MUST be excluded
from the path computation.
3.3.1.2. Path Computation with No Ordering Constraint
For an MPLS LSP which has no constraint on packet ordering except
that microflows must remain in order and does not contain other LSP
with ordering constraints, any link for which the Multipath Enabled
bit is set can be used. If s link is advertised as a Link Bundle and
the Multipath Enabled bit is set for the link, the available
bandwidth SHOULD be taken from the "Unreserved Bandwidth" rather than
the "Maximum LSP Bandwidth" (see [RFC4201]).
For most LSP, the bandwidth requirement of the largest microflow is
not known but an upper bound is known. For example if the LSP
aggregates pseudowires or other LSP of no more than some maximum
capacity or LSP which have signaled a microflow upper bound, then an
upper bound on the largest microflow is known. If this upper bound
exceeds the "Maximum LSP Bandwidth" of a given link, then that link
MUST be excluded from the path computation.
3.3.1.3. Path Computation for MPLS containing MPLS-TP
To carry LSP which have strict packet ordering requirements and do
not have the Entropy Label Used flag set as a client within a server
LSP that do not have strict packet ordering requirements, Entropy
Label must be added at the server layer LSP to traverse any link or
FA that has the Multipath Enabled bit set. For these LSP links which
have the Multipath Enabled bit set and the Entropy Label Multipath
bit clear MUST be excluded from the path computation.
If the LSR is not capable of adding an Entropy Label, then to carry
any client LSP with the Entropy Label Used clear and the OA Depth set
to a non-zero value, the server LSP SHOULD exclude any link or FA
that has the Multipath Enabled bit set. For these LSP, any link or
FA that has the Multipath Enabled bit set and cannot carry a
microflow as large as the entire LSP MUST be excluded from the path
computation. These LSP MAY be signaled as having strict packet
ordering requirements if they can be carried as a single microflow,
but this practice is NOT RECOMMENDED.
3.3.2. Link IP Capabilities and Path Computation
An MPLS-TP LSP cannot be reordered. There may be other types of LSP
with strict packet ordering requirements. If LSP with strict packet
ordering requirements carry IP, using IP headers in the multipath
load distribution would violate the packet ordering requirements.
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Some LSP cannot be reordered but do not carry IP, and do not carry
payloads which could be mistaken as IP. For example, any LSP
carrying only pseudowire traffic, where all pseudowires are using a
control word carries no payloads which could be mistaken as IP.
These type of LSP can be carried within MPLS LSP that allow use of IP
header information in multipath load distribution.
This section focuses on Cases in which links or FA must be excluded
from path computation based on the setings of the IP related Flags
bits in the Multipath Link Capability TLV.
3.3.2.1. LSP without Packet Ordering Requirements
Many LSP carry only IP or predominantly IP, use no hierarchy or have
little diversity in the MPLS label stack, and carry far more traffic
than can be carried over a single component link in a multipath.
Many LSP due to their high capacity, must traverse only multipath
which will use IP header information in the multipath traffic
distribution.
For these LSP, links must be excluded from the path computation which
do not have the IPv4 Enabled Multipath and IPv6 Enabled Multipath bit
set (if carrying both IPv4 and IPv6) and do not have either the
Default to IP/MPLS Multipath bit set or the IP Optional Multipath bit
set.
Hierarchical PSC LSP which require the use IP header information in
the multipath traffic distribution MUST NOT set the Ordered Aggregate
Enabled bit, MUST set the Default to IP/MPLS Multipath bit, and MUST
NOT set the IP Optional Multipath bit in the FA advertisement. The
IP Optional Multipath bit MUST be clear because the LSP cannot change
the behavior of midpoint LSR, except perhaps in the case of single
hop LSP.
3.3.2.2. LSP with Ordering Requirements
The only time that links or FA with both the Ordered Aggregate
Enabled bit and the Entropy Label Multipath bit clear can be used is
a special case for MPLS-TP LSP that carry only IP traffic. This case
does not apply if the MPLS_TP LSP is carrying other LSP or if it is
carrying pseudowires.
Where MPLS-TP LSP are carrying only IP, any link or FA with both the
Ordered Aggregate Enabled bit and the Entropy Label Multipath bit
clear for which the use of IP header information is not disabled or
cannot be disabled on a per LSP basis, that link MUST be excluded
from the path computation.
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Where MPLS-TP LSP are carrying only IP, links MAY be included in the
path computation have the IPv4 Enabled Multipath and IPv6 Enabled
Multipath bits clear, or have the Default to IP/MPLS Multipath bit
clear, or have the IP Optional Multipath bit set. Links with the IP
Optional Multipath set, MUST disable use of IP in the load balance
for LSP with the IP Multipath Allowed bit clear.
An MPLS-TP LSP are carrying only IP MUST have OA Depth set to one and
LSP Min Depth set to one and the IP Multipath Allowed bit cleared.
Call admission SHOULD NOT reject an LSP on the basis of OA Depth
being set to one if use of IP headers is always disabled, or can be
disabled for the specific LSP. If an MPLS-TP is set up this way end
then does start to carry other LSP or carry pseudowires, then
reordering within the MPLS-TP LSP will occur.
3.3.3. Link Depth Limitations and Path Computation
For any LSP which does not have strict packet ordering constraints,
LSP configuration SHOULD include the following parameters.
LSP Min Depth
a minimal acceptable number of label used in multipath traffic
distribution,
LSP IP Depth
a minimal label stack depth where the IP header can be used in
multipath traffic distribution
For example, if a PSC LSP will carry LSP which in turn carry very
high capacity pseudowires using the pseudowire flow label (see
[RFC6391]), the flow label is four labels deep. In this case, LSP
Min Depth should be four or higher.
For example, if the same PSC LSP will carry LSP which carry IP
traffic with no additional labels, then the IP header is two labels
deep. In this case, LSP IP Depth should be two or higher.
For an LSP with non-zero LSP Min Depth, all links with Max Depth set
to a value below LSP Min Depth MUST be excluded from the LSP Path
Computation.
For an LSP with non-zero LSP IP Depth, all links with IP Depth set to
a value below LSP IP Depth MUST be excluded from the LSP Path
Computation.
If all LSP carried an accurate LSP Min Depth and LSP IP Depth then
neither of these parameters would ever have to be configured. In a
network with legacy LSR, it may be necessary to configure these
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parameters for some LSP. A per-LSP minimum value of each parameter
SHOULD be configurable.
4. Backwards Compatibility
Networks today use three forms of multipath.
1. IP ECMP, including IP ECMP at LER using more than one LSP.
2. Ethernet Link Aggregation [IEEE-802.1AX].
3. MPLS Link Bundling [RFC4201].
4.1. Legacy Multipath Behavior
IP ECMP and Ethernet Link Aggregation always distribute traffic over
the entire multipath either using information in the MPLS label
stack, or using information in a potential IP header, or using both
types of information.
One of two behaviors is assumed for link bundles. Either the link
bundles place each LSP in its entirety on a single link bundle
component link for all LSP, or link bundles distribute traffic over
the entire link bundle using the same techniques used for ECMP and
Ethernet Link Aggregation. This second behavior is known as the "all
ones" component link (see [RFC4201]).
4.2. Networks without Multipath Extensions
Networks exist that are comprised entirely of LSR which do not
support these multipath extensions. In these networks there is no
way of telling how multipath links will behave. Since an Ethernet
Link Aggregation Goup (LAG) is advertised as an ordinary link, there
is no way to tell that it is a LAG and not an ordinary link.
4.2.1. Netowrks with MP Capability on all Multipath
Most large core network today rely heavily on the use of multipath.
Ethernet Link Aggregation is heavily used and LSR are configured to
use the "all ones" component link for all LSP. The "all ones"
component link is the default for many Link Bundling implementations
used in core networks.
This is equivalent to the following setting in the Multipath Node
Capabilities sub-TLV or Multipath Link Capabilities sub-TLV.
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1. Clear the Ordered Aggregate Enabled bit and the IP Optional
Multipath bit.
2. Set the Multipath Enabled bit, set the Default to Multipath bit,
and clear the Entropy Label Multipath bit.
3. If the label stack is used in the multipath traffic distribution,
set Max Depth to the number of label stack entries supported,
otherwise set it to zero.
4. Since Entropy Label support is not yet widespread, most LSR would
behave as if Entropy Label Multipath were clear.
5. If an IP packet under the label stack can be used in the
multipath traffic distribution (very common, almost universal in
core LSR), set IPv4 Enabled Multipath, set IPv6 Enabled
Multipath, set Default to IP/MPLS Multipath, and set IP Depth to
the maximum number of label stack entries which can be skipped
over before finding the IP stack. Otherwise clear IPv4 Enabled
Multipath, clear IPv6 Enabled Multipath and clear Default to IP/
MPLS Multipath.
6. On core networks where UDP and TCP ports are rarely used in
multipath, clear all UDP and TCP related bits. On networks where
multipath is configured to use TCP and UDP port numbers, these
bits would be set.
These networks can support very large LSP but cannot support LSP
which require strict packet ordering with other labels below such an
LSP, such as pseudowire labels. They may also misroute OAM packet
which use GAL (see [RFC5586]) if they use the GAL label in
determining the load balance. Generally the Link Bundle
advertisements indicate a "Maximum LSP Bandwidth" that is equal to
the "Unreserved Bandwidth" if Link Bundling is used with the all-ones
component link.
Good or bad, if the behavior is consistent, defaults can be
configured in other LSR, such that an accurate guess can be made when
no Multipath Link Capability TLV is available for a given link.
For example, in many networks, any link of 10 Gb/s or less can be
assumed to be a plain link (no multipath) while any link with a
capacity greater than 10 Gb/s can be assumed to be a multipath These
assumptions would hold if no 40 Gb/s or 100 Gb/s links are used.
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4.2.2. Netowrks with OA Capability on all Multipath
Some networks, particularly edge networks which tend to be lower
capacity, do not use Link Aggregation, and if they use Link Bundling
at all, configure each LSR to place each LSP in its entirety on a
single link bundle component link for all LSP. Some edge equipment
only supports this link bundle behavior.
This is equivalent to the following setting in the Multipath Node
Capabilities sub-TLV or Multipath Link Capabilities sub-TLV.
Set the Ordered Aggregate Enabled bit,
Clear the Multipath Enabled bit.
All remaining bits in the Flags field should be clear.
The Max Depth and IP Depth should be set to zero.
These networks can support LSP which require strict packet ordering,
but cannot support very large LSP.
Like the behavior described in Section 4.2.1, whether this behavior
is good or bad, defaults can be configured which accurately guess the
capabilities of links for which no Multipath Link Capability TLV is
available.
4.2.3. Legacy Netowrks with Mixed MP and OA Links
Some network may support Ethernet Link Aggregation and all or a
subset of LSR which place each LSP in its entirety on a single link
bundle component link for all LSP.
If the "Maximum LSP Bandwidth" is set as described in Section 4.2.1,
then very large LSP can be supported over link bundles. Very large
LSP cannot be supported on LSR which place each LSP in its entirety
on a single link bundle component link for all LSP, but these are
clearly indicated in signaling,
In these mixed networks it may not be possible to reliably support
LSP which require strict packet ordering. It is not possible to know
where Ethernet Link Aggregation is used and it is not possible to
accurately determine Link Bundling behavior on link bundles where
"Maximum LSP Bandwidth" is equal to "Unreserved Bandwidth".
Upgrading LSR to support Entropy Label on both LAG and Link Bundles
would improve the ability to carry LSP which require strict packet
ordering. To gain any benefit the LSP ingress would have to add ELI
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and EL.
If not all LSR are upgraded, then the MPLS TE multipath extensions
identify those LSR and multipath that have been upgraded.
4.3. Transition to Multipath Extension Support
If a Multipath Node Capability sub-TLV is not advertised (see
Section 2.1), then the LSR does not support these multipath
extensions. This allows detection of such nodes and if necessary
application of defaults to cover legacy multipath such as typical
Ethernet Link Aggregation Behavior.
4.3.1. Simple Transitions
For networks with LSR that do not support multipath extensions,
transition is easiest if all legacy LSR support and are configured
with a common link bundling behavior. If Ethernet Link Aggregation
is not used, a single configured default is needed to cover LSR that
do not advertise a Multipath Node Capability sub-TLV.
If Ethernet Link Aggregation had been previously used on Legacy LSR,
if possible LAG should be disabled and the members of the former LAG
configured and advertised as a link bundle which uses the equivalent
"all ones" behavior.
If Ethernet Link Aggregation remains but can be identified in some
way, such as links with capacity in excess of some value (for
example: greater than 10 Gb/s), then defaults can be set up for these
LAG. Alternately administrative attributes could be used [RFC3209].
The transition network in this case lacks the ability to determine
the largest microflow that can pass through legacy nodes, but this
was the case prior to transition for the entire network prior to
transition.
4.3.2. More Challenging Transitions
Transition is made more difficult if legacy LSR in a network support
Ethernet Link Aggregation but do not support Link Bundle and cannot
be identified by simple means, or the newer LSR lack sufficient
configuration capability to support conditional defaults.
This situation is most easily handled if a small upgrade to such an
LSR can advertise a fixed Multipath Node Capability sub-TLV giving
the characteristics of the Ethernet Link Aggregation implementation
on that node. Absent of such cooperation, the problem can be solved
by configuration on newer LSR which allows association of a Multipath
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Internet-Draft MPLS TE Multipath Extensions October 2012
Node Capability sub-TLV with a specific legacy router ID and possibly
a legacy router ID and link.
LSR supporting Multipath Extensions will need to assign default
values through configuration to these legacy LSR running Ethernet
Link Aggregation. These default values serve to allow LSP which
require strict packet ordering to avoid these legacy LSR.
LSR which do not support [RFC4201] may be sufficiently rare that the
ability to assign default values per legacy LSR or per [RFC3209]
administrative attribute may not be needed in practice.
5. IANA Considerations
[ ... to be completed ... ]
The symbolic constants IANA-TBD-1 through IANA-TBD-3 need to be
replaced. Complete instructions, including identification of the
number space for each of these will be added to a later version of
this internet-draft.
6. Security Considerations
The combination of MPLS, MPLS-TP, and multipath does not introduce
any new security threats. The security considerations for MPLS/GMPLS
and for MPLS-TP are documented in [RFC5920] and
[I-D.ietf-mpls-tp-security-framework].
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.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
[RFC5420] Farrel, A., Papadimitriou, D., Vasseur, JP., and A.
Ayyangarps, "Encoding of Attributes for MPLS LSP
Establishment Using Resource Reservation Protocol Traffic
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Internet-Draft MPLS TE Multipath Extensions October 2012
Engineering (RSVP-TE)", RFC 5420, February 2009.
[RFC5786] Aggarwal, R. and K. Kompella, "Advertising a Router's
Local Addresses in OSPF Traffic Engineering (TE)
Extensions", RFC 5786, March 2010.
7.2. Informative References
[I-D.ietf-mpls-entropy-label]
Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
draft-ietf-mpls-entropy-label-06 (work in progress),
September 2012.
[I-D.ietf-mpls-tp-security-framework]
Fang, L., Niven-Jenkins, B., Mansfield, S., and R.
Graveman, "MPLS-TP Security Framework",
draft-ietf-mpls-tp-security-framework-04 (work in
progress), July 2012.
[I-D.villamizar-mpls-tp-multipath]
Villamizar, C., "Use of Multipath with MPLS-TP and MPLS",
draft-villamizar-mpls-tp-multipath-03 (work in progress),
October 2012.
[IEEE-802.1AX]
IEEE Standards Association, "IEEE Std 802.1AX-2008 IEEE
Standard for Local and Metropolitan Area Networks - Link
Aggregation", 2006, <http://standards.ieee.org/getieee802/
download/802.1AX-2008.pdf>.
[ITU-T.G.800]
ITU-T, "Unified functional architecture of transport
networks", 2007, <http://www.itu.int/rec/T-REC-G/
recommendation.asp?parent=T-REC-G.800>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999.
[RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, November 2000.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
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Internet-Draft MPLS TE Multipath Extensions October 2012
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, April 2002.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC6107] Shiomoto, K. and A. Farrel, "Procedures for Dynamically
Signaled Hierarchical Label Switched Paths", RFC 6107,
February 2011.
[RFC6391] Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
J., and S. Amante, "Flow-Aware Transport of Pseudowires
over an MPLS Packet Switched Network", RFC 6391,
November 2011.
Author's Address
Curtis Villamizar (editor)
Outer Cape Cod Network Consulting
Email: curtis@occnc.com
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