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Versions: (draft-li-hierarchical-isis) 00

Internet Engineering Task Force                                    T. Li
Internet-Draft                                           Arista Networks
Intended status: Standards Track                        December 7, 2018
Expires: June 10, 2019


                           Hierarchical IS-IS
                 draft-li-lsr-isis-hierarchical-isis-00

Abstract

   The IS-IS routing protocol was originally defined with a two level
   hierarchical structure.  This was adequate for the networks at the
   time.  As we continue to expand the scale of our networks, it is
   apparent that additional hierarchy would be a welcome degree of
   flexibility in network design.

   This document defines IS-IS Levels 3 through 8.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on June 10, 2019.

Copyright Notice

   Copyright (c) 2018 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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  PDU changes . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Circuit Type  . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  PDU Type  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Additional PDUs . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  LAN IS to IS hello PDU (LAN-HELLO-PDU)  . . . . . . . . .   4
     3.2.  Point-to-point IS to IS hello PDU (P2P-HELLO-PDU) . . . .   4
     3.3.  Level n Link State PDU (Ln-LSP-PDU) . . . . . . . . . . .   4
     3.4.  Level n complete sequence numbers PDU (Ln-CSNP-PDU) . . .   5
     3.5.  Level n partial sequence numbers PDU (Ln-PSNP-PDU)  . . .   5
   4.  Inheritance of TLVs . . . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  PDU Type  . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.2.  New PDUs  . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The IS-IS routing protocol IS-IS [ISO10589] currently supports a two
   level hierarchy of abstraction.  The fundamental unit of abstraction
   is the 'area', which is a (hopefully) connected set of systems
   running IS-IS at the same level.  Level 1, the lowest level, is
   abstracted by routers that participate in both Level 1 and Level 2.

   Practical considerations, such as the size of an area's link state
   database, cause network designers to restrict the number of routers
   in any given area.  Concurrently, the dominance of scale-out
   architectures based around small routers has created a situation
   where the scalability limits of the protocol are going to become
   critical in the foreseeable future.

   The goal of this document is to enable additional hierarchy within
   IS-IS by creating additional hierarchy.  Each additional level of
   hierarchy has a multiplicative effect on scale, so the addition of
   six levels should be a significant improvement.  While all six levels
   may not be needed in the short term, it is apparent that the original
   designers of IS-IS reserved enough space for these levels, and
   defining six additional levels is only slightly harder than adding a




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   single level, so it makes some sense to expand the design for the
   future.

   The modifications described herein are designed to be fully backward
   compatible.

   Section references in this document are references to sections of IS-
   IS [ISO10589].

1.1.  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].

2.  PDU changes

   In this section, we enumerate all of the redefinitions of protocol
   header fields necessary to add additional levels.

2.1.  Circuit Type

   In the fixed header of some IS-IS PDUs, a field is named 'Reserved/
   Circuit Type' (Section 9.5).  The high order six bits are reserved,
   with the low order two bits indicating Level 1 (bit 1) and Level 2
   (bit 2).

   This field is renamed to be 'Circuit Type'.  The bits are redefined
   as follows:

   1.  Level 1

   2.  Level 2

   3.  Level 3

   4.  Level 4

   5.  Level 5

   6.  Level 6

   7.  Level 7

   8.  Level 8

   The value of zero (no bits set) is reserved.  PDUs with a Circuit
   Type of zero SHALL be ignored.



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   The set bits of the Circuit Type MUST be contiguous.  If bit n and
   bit m are set in the Circuit Type, then all bits in the interval
   [n:m] must be set.

2.2.  PDU Type

   The fixed header of IS-IS PDUs contains an octet with three reserved
   bits and the 'PDU Type' field.  The three reserved bits are
   transmitted as zero and ignored on receipt.  (Section 9.5)

   To allow for additional PDU space, this entire octet is renamed the
   'PDU Type' field.

3.  Additional PDUs

3.1.  LAN IS to IS hello PDU (LAN-HELLO-PDU)

   The 'LAN IS to IS hello PDU' (LAN-HELLO-PDU) is identical in format
   to the 'Level 2 LAN IS to IS hello PDU' (Section 9.6), except that
   the PDU Type has value AAA.  The LAN-HELLO-PDU MUST be used instead
   of the 'Level 1 LAN IS to IS hello PDU' (Section 9.5) or the 'Level 2
   LAN IS to IS hello PDU' on any circuit that has one or more of Level
   3 through Level 8 enabled.

3.2.  Point-to-point IS to IS hello PDU (P2P-HELLO-PDU)

   The 'Point-to-point IS to IS hello PDU' can be used on circuits of
   any Level without modification.

3.3.  Level n Link State PDU (Ln-LSP-PDU)

   The 'Level n Link State PDU' (Ln-LSP-PDU) has the same format as the
   'Level 2 Link State PDU' (Section 9.9), except for the PDU Type.  The
   PDU Types for Levels 3 through 8 are defined as follows:

      Level 3 (L3-LSP-PDU): BBB

      Level 4 (L4-LSP-PDU): CCC

      Level 5 (L5-LSP-PDU): DDD

      Level 6 (L6-LSP-PDU): EEE

      Level 7 (L7-LSP-PDU): FFF

      Level 8 (L8-LSP-PDU): GGG





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3.4.  Level n complete sequence numbers PDU (Ln-CSNP-PDU)

   The 'Level n complete sequence numbers PDU' (Ln-CSNP-PDU) has the
   same format as the 'Level 2 complete sequence numbers PDU'
   (Section 9.11), except for the PDU Type.  The PDU Types for Levels 3
   through 8 are defined as follows:

      Level 3 (L3-CSNP-PDU): HHH

      Level 4 (L4-CSNP-PDU): III

      Level 5 (L5-CSNP-PDU): JJJ

      Level 6 (L6-CSNP-PDU): KKK

      Level 7 (L7-CSNP-PDU): LLL

      Level 8 (L8-CSNP-PDU): MMM

3.5.  Level n partial sequence numbers PDU (Ln-PSNP-PDU)

   The 'Level 2 partial sequence numbers PDU' (Ln-PSNP-PDU) has the same
   format as the 'Level 2 partial sequence numbers PDU' (Section 9.13),
   except for the PDU Type.  The PDU Types for Levels 3 through 8 are
   defined as follows:

      Level 3 (L3-PSNP-PDU): NNN

      Level 4 (L4-PSNP-PDU): OOO

      Level 5 (L5-PSNP-PDU): PPP

      Level 6 (L6-PSNP-PDU): QQQ

      Level 7 (L7-PSNP-PDU): RRR

      Level 8 (L8-PSNP-PDU): SSS

4.  Inheritance of TLVs

   All existing Level 2 TLVs may be used in the corresponding Level 3
   through Level 8 PDUs.  When used in a Level 3 through Level 8 PDU,
   the semantics of these TLVs will be applied to the Level of the
   containing PDU.  If the original semantics of the PDU was carrying a
   reference to Level 1 in a Level 2 TLV, then the semantics of the TLV
   at level N will be a reference to level N-1.  The intent is to retain
   the original semantics of the TLV at the higher level.




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5.  Acknowledgements

   The author would like to thank Dinesh Dutt for inspiring this
   document.

6.  IANA Considerations

   This document makes many requests to IANA, as follows:

6.1.  PDU Type

   The existing IS-IS PDU registry currently supports values 0-31.  This
   should be expanded to support the values 0-255.  The existing value
   assignments should be retained.  Value 255 should be reserved.

6.2.  New PDUs

   IANA is requested to allocate values from the IS-IS PDU registry for
   the following:

      LAN-HELLO-PDU: AAA

      L3-LSP-PDU: BBB

      L4-LSP-PDU: CCC

      L5-LSP-PDU: DDD

      L6-LSP-PDU: EEE

      L7-LSP-PDU: FFF

      L8-LSP-PDU: GGG

      L3-CSNP-PDU: HHH

      L4-CSNP-PDU: III

      L5-CSNP-PDU: JJJ

      L6-CSNP-PDU: KKK

      L7-CSNP-PDU: LLL

      L8-CSNP-PDU: MMM

      L3-PSNP-PDU: NNN




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      L4-PSNP-PDU: OOO

      L5-PSNP-PDU: PPP

      L6-PSNP-PDU: QQQ

      L7-PSNP-PDU: RRR

      L8-PSNP-PDU: SSS

   To allow for PDU types to be defined independent of this document,
   the above values should be allocated from the range 32-254.

7.  Security Considerations

   This document introduces no new security issues.  Security of routing
   within a domain is already addressed as part of the routing protocols
   themselves.  This document proposes no changes to those security
   architectures.

8.  Normative References

   [ISO10589]
              International Organization for Standardization,
              "Intermediate System to Intermediate System Intra-Domain
              Routing Exchange Protocol for use in Conjunction with the
              Protocol for Providing the Connectionless-mode Network
              Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002.

   [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>.

Author's Address

   Tony Li
   Arista Networks
   5453 Great America Parkway
   Santa Clara, California  95054
   USA

   Email: tony.li@tony.li








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