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).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.
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 ReferencesBorder Gateway Protocol - Link State (BGP-LS) Extensions for Segment RoutingInformative ReferencesAcknowledgementsThe 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:NokiaAntwerpBelgium gunter.van_de_velde@nokia.com NokiaBelgium wim.henderickx@nokia.com ArrcusUnited States of Americakeyur@arrcus.com