Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-ISCapitalonlinexiaohu.xu@capitalonline.netsriganeshkini@gmail.comCisco Systems, Inc.Eurovea Centre, Central 3Pribinova Street 10Bratislava81109Slovakiappsenak@cisco.comCisco Systems, Inc.BrusselsBelgiumcfilsfil@cisco.comCisco Systems, Inc.La RigourdiereCesson SevigneFranceslitkows@cisco.comNokiaAztec West Business ParkBristol740 Waterside DriveBS32 4UFUnited Kingdommatthew.bocci@nokia.com
RTG
LSRMultiprotocol Label Switching (MPLS) has defined a mechanism to load-balance
traffic flows using Entropy Labels (EL). An ingress Label
Switching Router (LSR) cannot insert ELs for packets going into a given
Label Switched Path (LSP) unless an egress LSR has indicated via signaling that it has the
capability to process ELs, referred to as the Entropy Label Capability
(ELC), on that LSP. In addition, it would be useful for ingress LSRs
to know each LSR's capability for reading the maximum label stack depth
and performing EL-based load-balancing, referred to as Entropy Readable
Label Depth (ERLD). This document defines a mechanism to signal these two
capabilities using IS-IS and Border Gateway Protocol - Link State (BGP-LS).Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
.
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Table of Contents
. Introduction
. Terminology
. Advertising ELC Using IS-IS
. Advertising ERLD Using IS-IS
. Signaling ELC and ERLD in BGP-LS
. IANA Considerations
. Security Considerations
. References
. Normative References
. Informative References
Acknowledgements
Contributors
Authors' Addresses
Introduction describes a method to
load-balance Multiprotocol Label Switching (MPLS) traffic flows using
Entropy Labels (EL). It also introduces the concept of Entropy Label
Capability (ELC) and defines the signaling of this capability via MPLS
signaling protocols. Recently, mechanisms have been defined to signal
labels via link-state Interior Gateway Protocols (IGP) such as IS-IS
. This document defines a
mechanism to signal the ELC using IS-IS. In cases where Segment Routing (SR) is used with the MPLS data plane
(e.g., SR-MPLS ), it would be
useful for ingress LSRs to know each intermediate LSR's capability of
reading the maximum label stack depth and performing EL-based
load-balancing. This capability, referred to as Entropy Readable Label
Depth (ERLD) as defined in ,
may be used by ingress LSRs to determine the position of the EL label in
the stack, and whether it's necessary to insert multiple ELs at
different positions in the label stack. This document defines a
mechanism to signal the ERLD using IS-IS.TerminologyThis memo makes use of the terms defined in ,
and .The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are
to be interpreted as described in BCP 14 when, and
only when, they appear in all capitals, as shown here.Advertising ELC Using IS-ISEven though ELC is a property of the node, in some cases it is
advantageous to associate and advertise the ELC with a prefix. In a
multi-area network, routers may not know the identity of the prefix
originator in a remote area or may not know the capabilities of such
originator. Similarly, in a multi-domain network, the identity of the
prefix originator and its capabilities may not be known to the ingress
LSR. Bit 3 in the Prefix Attribute Flags is used as the ELC Flag (E-Flag), as shown in . If a router has multiple interfaces, the router
MUST NOT announce the ELC for any local host prefixes
unless all of its interfaces are capable of processing ELs. If a router
supports ELs on all of its interfaces, it SHOULD set the
ELC for every local host prefix it advertises in IS-IS. Prefix Attribute Flags
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|X|R|N|E| ...
+-+-+-+-+-+-+-+-+...
E-Flag:
ELC Flag (Bit 3) - Set for local host prefix of the originating node if it
supports ELC on all interfaces.
The ELC signaling MUST be preserved when a router propagates a prefix
between IS-IS levels .
When redistributing a prefix between two IS-IS protocol instances or
redistributing from another protocol to an IS-IS protocol instance, a
router SHOULD preserve the ELC signaling for that prefix
if it exists. The exact mechanism used to exchange ELC between protocol
instances running on an Autonomous System Border Router is outside of
the scope of this document.Advertising ERLD Using IS-ISA new MSD-Type , called
ERLD-MSD, is defined to advertise the ERLD of a given router. An MSD-Type code 2 has been
assigned by IANA for ERLD-MSD. The MSD-Value field is set to the ERLD in
the range between 0 to 255. The scope of the advertisement depends on
the application. If a router has multiple interfaces with different
capabilities of reading the maximum label stack depth, the router
MUST advertise the smallest value found across all its
interfaces.The absence of ERLD-MSD advertisements indicates only that the advertising
node does not support advertisement of this capability.The considerations for advertising the ERLD are specified in
.If the ERLD-MSD type is received in the Link MSD sub-TLV,
it MUST be ignored.Signaling ELC and ERLD in BGP-LSThe IS-IS extensions defined in this document can be advertised via
BGP-LS (distribution of Link-State and TE information using BGP)
using existing BGP-LS TLVs.The ELC is advertised using the Prefix Attribute Flags TLV as defined in
.The ERLD-MSD is advertised using the Node MSD TLV as defined in
.IANA ConsiderationsIANA has completed the following actions for this document:
Bit 3 in the "Bit Values for Prefix Attribute Flags Sub-TLV" registry has
been assigned to the ELC Flag. IANA has updated the registry to
reflect the name used in this document: ELC Flag (E-Flag).
Type 2 in the "IGP MSD-Types" registry has been assigned for the ERLD-MSD.
IANA has updated the registry to reflect the name used in this
document: ERLD-MSD.
Security ConsiderationsThis document specifies the ability to advertise additional node
capabilities using IS-IS and BGP-LS. As such, the security
considerations as described in , , , , , , and are applicable to this document.Incorrectly setting the E-Flag during origination, propagation, or
redistribution may lead to poor or no load-balancing of the MPLS traffic
or to MPLS traffic being discarded on the egress node.Incorrectly setting the ERLD value may lead to poor or no load-balancing of the
MPLS traffic.ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Domain-Wide Prefix Distribution with Two-Level IS-ISThis document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support optimal routing within a two-level domain. The IS-IS protocol is specified in ISO 10589, with extensions for supporting IPv4 (Internet Protocol) specified in RFC 1195. This document replaces RFC 2966.This document extends the semantics presented in RFC 1195 so that a routing domain running with both level 1 and level 2 Intermediate Systems (IS) (routers) can distribute IP prefixes between level 1 and level 2, and vice versa. This distribution requires certain restrictions to ensure that persistent forwarding loops do not form. The goal of this domain-wide prefix distribution is to increase the granularity of the routing information within the domain. [STANDARDS-TRACK]The Use of Entropy Labels in MPLS ForwardingLoad balancing is a powerful tool for engineering traffic across a network. This memo suggests ways of improving load balancing across MPLS networks using the concept of "entropy labels". It defines the concept, describes why entropy labels are useful, enumerates properties of entropy labels that allow maximal benefit, and shows how they can be signaled and used for various applications. This document updates RFCs 3031, 3107, 3209, and 5036. [STANDARDS-TRACK]North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGPIn a number of environments, a component external to a network is called upon to perform computations based on the network topology and current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network.This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual IGP links. The mechanism described is subject to policy control.Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs).IS-IS Prefix Attributes for Extended IPv4 and IPv6 ReachabilityThis document introduces new sub-TLVs to support advertisement of IPv4 and IPv6 prefix attribute flags and the source router ID of the router that originated a prefix advertisement.IS-IS Extensions for Advertising Router InformationThis document defines a new optional Intermediate System to Intermediate System (IS-IS) TLV named CAPABILITY, formed of multiple sub-TLVs, which allows a router to announce its capabilities within an IS-IS level or the entire routing domain. This document obsoletes RFC 4971.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Signaling Maximum SID Depth (MSD) Using IS-ISThis document defines a way for an Intermediate System to Intermediate System (IS-IS) router to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity. Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment ID (SID) stack can be supported in a given network. This document only defines one type of MSD: Base MPLS Imposition. However, it defines an encoding that can support other MSD types. This document focuses on MSD use in a network that is Segment Routing (SR) enabled, but MSD may also be useful when SR is not enabled.Entropy Label for Source Packet Routing in Networking (SPRING) TunnelsSegment Routing (SR) leverages the source-routing paradigm. A node steers a packet through an ordered list of instructions, called segments. Segment Routing can be applied to the Multiprotocol Label Switching (MPLS) data plane. Entropy labels (ELs) are used in MPLS to improve load-balancing. This document examines and describes how ELs are to be applied to Segment Routing MPLS.Signaling Maximum SID Depth (MSD) Using the Border Gateway Protocol - Link StateThis document defines a way for a Border Gateway Protocol - Link State (BGP-LS) speaker to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity.Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment Identifier (SID) stack can be supported in a given network.Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment RoutingInformative ReferencesSegment Routing with the MPLS Data PlaneSegment Routing (SR) leverages the source-routing paradigm. A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. In the MPLS data plane, the SR header is instantiated through a label stack. This document specifies the forwarding behavior to allow instantiating SR over the MPLS data plane (SR-MPLS).IS-IS Extensions for Segment RoutingSegment Routing (SR) allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF).This document describes the IS-IS extensions that need to be introduced for Segment Routing operating on an MPLS data plane.AcknowledgementsThe authors would like to thank , , , ,
, , , , ,
and for their valuable comments.ContributorsThe following people contributed to the content
of this document and should be considered as coauthors:NokiaAntwerpBelgiumgunter.van_de_velde@nokia.comNokiaBelgiumwim.henderickx@nokia.comArrcusUnited States of Americakeyur@arrcus.comAuthors' AddressesCapitalonlinexiaohu.xu@capitalonline.netsriganeshkini@gmail.comCisco Systems, Inc.Eurovea Centre, Central 3Pribinova Street 10Bratislava81109Slovakiappsenak@cisco.comCisco Systems, Inc.BrusselsBelgiumcfilsfil@cisco.comCisco Systems, Inc.La RigourdiereCesson SevigneFranceslitkows@cisco.comNokiaAztec West Business ParkBristol740 Waterside DriveBS32 4UFUnited Kingdommatthew.bocci@nokia.com