Network Working Group X. Xu
Internet-Draft Alibaba Inc
Intended status: Standards Track S. Kini
Expires: March 6, 2020
P. Psenak
C. Filsfils
Cisco
S. Litkowski
Orange
September 3, 2019
Signaling Entropy Label Capability and Entropy Readable Label Depth
Using IS-IS
draft-ietf-isis-mpls-elc-08
Abstract
Multiprotocol 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 Entropy Label Capability (ELC), on that tunnel. 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. These mechanisms are particularly useful, where label
advertisements are done via protocols like IS-IS.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 6, 2020.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Advertising ERLD Using IS-IS . . . . . . . . . . . . . . . . 3
4. Advertising ELC Using IS-IS . . . . . . . . . . . . . . . . . 3
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. BGP-LS Extension . . . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[RFC6790] describes a method to load-balance Multiprotocol Label
Switching (MPLS) traffic flows using Entropy Labels (EL). "The Use
of Entropy Labels in MPLS Forwarding" [RFC6790] introduces the
concept of Entropy Label Capability (ELC) and defines the signalings
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
[I-D.ietf-isis-segment-routing-extensions]. In such scenarios, the
defined signaling mechanisms 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 LSPs are used for whatever reasons
(e.g., SR-MPLS [I-D.ietf-spring-segment-routing-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 [I-D.ietf-mpls-spring-entropy-label] may
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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.
2. Terminology
This memo makes use of the terms defined in [RFC6790] and [RFC4971].
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Advertising ERLD Using IS-IS
A new MSD-type of the Node MSD sub-TLV [RFC8491], called ERLD is
defined to advertise the ERLD of a given router. As shown in
Figure 2, it is formatted as described in [RFC8491] 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 line-cards with different capabilities of reading
the maximum label stack depth, the router MUST advertise the smallest
one.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type=TBD2 | ERLD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: ERLD MSD-Type Format
4. Advertising ELC Using IS-IS
Even 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.
One bit of the "Bit Values for Prefix Attribute Flags Sub-TLV"
registry defined in [RFC7794] (Bit 3 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 for any prefixes that are locally
attached unless all of its line-cards are capable of processing ELs.
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If a router supports ELs on all of its line-cards, it SHOULD set the
ELC for every local host prefix it advertises in IS-IS.
When a router leaks a prefix between two levels (upwards or
downwards), it MUST preserve the ELC signaling for this prefix.
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|X|R|N|E| ...
+-+-+-+-+-+-+-+-+...
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. The exact
mechanism used to exchange ELC between protocol instances running on
an ASBR is outside of the scope of this document and is
implementation specific.
5. Acknowledgements
The authors would like to thank Yimin Shen, George Swallow, Acee
Lindem, Les Ginsberg, Ketan Talaulikar, Jeff Tantsura, Bruno Decraene
Carlos Pignataro, Wim Hendrickx, and Gunter Van De Velde for their
valuable comments.
6. BGP-LS Extension
The IS-IS extensions defined in this document can be advertised via
BGP-LS [RFC7752] using existing BGP-LS TLVs.
The ELC Flag included in the Prefix Attribute Flags sub-TLV, as
defined in Section 4, is advertised using the Prefix Attribute Flags
TLV (TLV 1170) of the BGP-LS IPv4/IPv6 Prefix NLRI Attribute as
defined in section 2.3.2 of
[I-D.ietf-idr-bgp-ls-segment-routing-ext].
The ERLD MSD-type introduced for IS-IS in Section 3 is advertised
using the Node MSD TLV (TLV 266) of the BGP-LS Node NLRI Attribute as
defined in section 3 of [I-D.ietf-idr-bgp-ls-segment-routing-ext].
7. IANA Considerations
IANA is requested to allocate the E-bit (bit position 3 is desired)
from the "Bit Values for Prefix Attribute Flags Sub-TLV" registry.
IANA is requested to allocate a MSD type (the type code of 2 is
desired) from the "IGP MSD Types" registry for ERLD.
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8. Security Considerations
The security considerations as described in [RFC4971] nd
[I-D.ietf-mpls-spring-entropy-label] are applicable to this document.
Incorrectly setting the E flag (ELC capable) (during origination,
leaking or redistribution) may lead to black-holing of the traffic on
the egress node.
9. Normative References
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., and B. Decraene, "IS-IS Extensions for
Segment Routing", draft-ietf-isis-segment-routing-
extensions-25 (work in progress), May 2019.
[I-D.ietf-mpls-spring-entropy-label]
Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy label for SPRING
tunnels", draft-ietf-mpls-spring-entropy-label-12 (work in
progress), July 2018.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
"Intermediate System to Intermediate System (IS-IS)
Extensions for Advertising Router Information", RFC 4971,
DOI 10.17487/RFC4971, July 2007,
<https://www.rfc-editor.org/info/rfc4971>.
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[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
Authors' Addresses
Xiaohu Xu
Alibaba Inc
Email: xiaohu.xxh@alibaba-inc.com
Sriganesh Kini
Email: sriganeshkini@gmail.com
Peter Psenak
Cisco
Email: ppsenak@cisco.com
Clarence Filsfils
Cisco
Email: cfilsfil@cisco.com
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Stephane Litkowski
Orange
Email: stephane.litkowski@orange.com
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