Signaling Entropy Label
Capability and Entropy Readable Label Depth Using IS-ISAlibaba Incxiaohu.xxh@alibaba-inc.comsriganeshkini@gmail.comCiscomsiva@cisco.comCiscocfilsfil@cisco.comOrangestephane.litkowski@orange.comMultiprotocol 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
tunnel unless an egress LSR has indicated via signaling that it has the
capability of processing ELs, referred to as Entropy Label Capability
(ELC), on that tunnel. In addition, it would be useful for ingress LSRs
to know each LSR's capability of reading the maximum label stack depth
and performing EL-based load-balancing, referred to as Entropy Readable
Label Depth (ERLD), in the cases where stacked LSPs are used for
whatever reasons. This document defines mechanisms to signal these two
capabilities using IS-IS. These mechanisms are useful when the label
advertisement is also done via IS-IS. In addition, this document
introduces the Non-IGP Functional Capabilities Sub-TLV for advertising
IS-IS router's actual non-IGP functional capabilities. ELC is one of
such non-IGP functional capabilities. describes a method to load balance
Multiprotocol Label Switching (MPLS) traffic flows using Entropy Labels
(EL). introduces the concept of Entropy Label
Capability (ELC) and defines the signalings of this capability via MPLS
signaling protocols. Recently, mechanisms are being defined to signal
labels via link-state Interior Gateway Protocols (IGP) such as IS-IS
. In such
scenario, the signaling mechanisms defined in
are inadequate. This draft defines a mechanism to signal the ELC using IS-IS. This mechanism is useful when the label
advertisement is also done via IS-IS.In addition, in the cases where stacked LSPs are used for whatever
reasons (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 whether it's necessary to insert an EL
for a given LSP of the stacked LSP tunnel in the case where there has
already been at least one EL in the label stack .This memo makes use of the terms defined in
and .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.This document defines the Non-IGP Functional Capabilities Sub-TLV
with Sub-TLV type of TBD1 within the body of the IS-IS Router Capability
TLV. An IS-IS router advertising an IS-IS Router Capability TLV MAY
include the Non-IGP Functional Capabilities Sub-TLV. The Sub-TLV MUST
reflect the advertising IS-IS router's actual non-IGP functional
capabilities in the flooding scope of the containing Router Capability
TLV.The format of the Router Non-IGP Functional Capabilities Sub-TLV is
as follows:Type: TBD1.Length: Indicates the length of the value portion in octets and
will be a multiple of 4 octets dependent on the number of
capabilities advertised. Initially, the length will be 4, denoting 4
octets of non-IGP functional capability bits.Value: A variable-length sequence of capability bits rounded to a
multiple of 4 octets padded with undefined bits. Initially, there
are 4 octets of capability bits. Bits are numbered left to right
starting with the most significant bit being bit 0.The Non-IGP Functional Capabilities Sub-TLV MAY be followed by
optional Sub-TLVs that further specify a non-IGP functional capability.
The specifications for non-IGP functional capabilities advertised in
this Sub-TLV MUST describe protocol behavior and address backwards
compatibility.One bit of the Non-IGP Functional Capability Bits (Bit 0 is desired)
is to be assigned by the IANA for the ELC . If a
router has multiple line cards, the router MUST NOT announce the ELC
unless all of its linecards are capable of
processing ELs.How to apply the ELC advertisement to the inter-area, inter-AS and
inter-protocol scenarios is outside the scope of this document.A new MSD-type of the Node MSD sub-TLV , called ERLD is defined to
advertise the ERLD of a given router. As shown in Figure 2, it is
formatted as described in with a new MSD-Type code to
be assigned by IANA (the type code of 2 is desired) and the 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
linecards with different capabilities of reading the maximum label stack
deepth, the router MUST advertise the smallest one.The authors would like to thank Yimin Shen, George Swallow, Acee
Lindem, Les Ginsberg, Ketan Talaulikar, Jeff Tantsura, Bruno Decraene
and Carlos Pignataro for their valuable comments.This document requests IANA to allocate one sub-TLV type of the
Router Capability TLV registry for the Non-IGP Functional Capabilities
Sub-TLV. Futhermore, this document requests IANA to creat a subregistry
for "Non-IGP Functional Capability Bits" within the "Interior Gateway
Protocol (IGP) Parameters" registry. This subregistry is comprised of
the fields Bit Number, Capability Name, and Reference. Initially, one
bit is reqested to be assigned for the ELC. The registration procedure
is "Expert Review" as defined in . The following
values are defined by this document:IANA is requested to allocate a MSD type (the type code of 2 is
desired) from the “IGP MSD Types” registry for ERLD.The security considerations as described in
is applicable to this document. This document does not introduce any new
security risk.