An Analysis of Scaling Issues in MPLS-TE Core Networks
RFC 5439

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Network Working Group                                        S. Yasukawa
Request for Comments: 5439                                           NTT
Category: Informational                                        A. Farrel
                                                      Old Dog Consulting
                                                             O. Komolafe
                                                           Cisco Systems
                                                           February 2009

         An Analysis of Scaling Issues in MPLS-TE Core Networks

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

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Abstract

   Traffic engineered Multiprotocol Label Switching (MPLS-TE) is
   deployed in providers' core networks.  As providers plan to grow
   these networks, they need to understand whether existing protocols
   and implementations can support the network sizes that they are
   planning.

   This document presents an analysis of some of the scaling concerns
   for the number of Label Switching Paths (LSPs) in MPLS-TE core
   networks, and examines the value of two techniques (LSP hierarchies
   and multipoint-to-point LSPs) for improving scaling.  The intention
   is to motivate the development of appropriate deployment techniques
   and protocol extensions to enable the application of MPLS-TE in large
   networks.

   This document only considers the question of achieving scalability
   for the support of point-to-point MPLS-TE LSPs.  Point-to-multipoint
   MPLS-TE LSPs are for future study.

Yasukawa, et al.             Informational                      [Page 1]
RFC 5439                   Scaling in MPLS-TE              February 2009

Table of Contents

   1. Introduction ....................................................3
      1.1. Overview ...................................................3
      1.2. Glossary of Notation .......................................5
   2. Issues of Concern for Scaling ...................................5
      2.1. LSP State ..................................................5
      2.2. Processing Overhead ........................................6
      2.3. RSVP-TE Implications .......................................6
      2.4. Management .................................................7
   3. Network Topologies ..............................................8
      3.1. The Snowflake Network Topology .............................9
      3.2. The Ladder Network Topology ...............................11
      3.3. Commercial Drivers for Selected Configurations ............14
      3.4. Other Network Topologies ..................................15
   4. Required Network Sizes .........................................16
      4.1. Practical Numbers .........................................16
   5. Scaling in Flat Networks .......................................16
      5.1. Snowflake Networks ........................................17
      5.2. Ladder Networks ...........................................18
   6. Scaling Snowflake Networks with Forwarding Adjacencies .........22
      6.1. Two-Layer Hierarchy .......................................22
           6.1.1. Tuning the Network Topology to Suit the
                  Two-Layer Hierarchy ................................23
      6.2. Alternative Two-Layer Hierarchy ...........................24
      6.3. Three-Layer Hierarchy .....................................25
      6.4. Issues with Hierarchical LSPs .............................26
   7. Scaling Ladder Networks with Forwarding Adjacencies ............27
      7.1. Two-Layer Hierarchy .......................................27
      7.2. Three-Layer Hierarchy .....................................28
      7.3. Issues with Hierarchical LSPs .............................29
   8. Scaling Improvements through Multipoint-to-Point LSPs ..........30
      8.1. Overview of MP2P LSPs .....................................30
      8.2. LSP State: A Better Measure of Scalability ................31
      8.3. Scaling Improvements for Snowflake Networks ...............32
           8.3.1. Comparison with Other Scenarios ....................33
      8.4. Scaling Improvements for Ladder Networks ..................34
           8.4.1. Comparison with Other Scenarios ....................36
           8.4.2. LSP State Compared with LSP Numbers ................37
      8.5. Issues with MP2P LSPs .....................................37