Cisco Express Forwarding by Nakia Stringfield - CCIE No 13451; Russ White CCIE No 2635; Stacia McKee Publisher: Cisco Press Pub Date: April 24, 2007 Print ISBN-10: 1-58705-236-9 Print ISBN-13: 978-1-58705-236-1 Pages: 288 Table of Contents | Index Overview Cisco Express Forwarding Understanding and troubleshooting CEF in Cisco routers and switches Nakia Stringfield, CCIÊ® No 13451 Russ White, CCIE No 2635 Stacia McKee How does a router switch a packet? What is the difference between routing a packet, switching a frame, and packet switching? What is the Cisco® Express Forwarding (CEF) feature referred to in Cisco documentation and commonly found in Cisco IOS® commands? CEF is a general term that describes the mechanism by which Cisco routers and Catalyst® switches packet-switch (route) frames CEF is found in almost all Cisco routers and Catalyst switches, and understanding how CEF operates can improve the performance, scalability, and efficiency of your network Cisco Express Forwarding demystifies the internal workings of Cisco routers and switches, making it easier for you to optimize performance and troubleshoot issues that arise in Cisco network environments This book addresses common misconceptions about CEF and packet switching across various platforms, helping you to improve your troubleshooting skills for CEF- and non-CEF-related problems The first part of the book provides an overview of packetswitching architectures and CEF operation and advanced features It also covers the enhanced CEF structure and general troubleshooting The second part of the book provides case studies that focus on the common topics that have been problematic for customers and those supporting Cisco networks Full of practical examples and configurations, this book draws on years of experience to help you keep your Cisco networks running efficiently Nakia Stringfield, CCIÊ® No 13451, is a network consulting engineer for Advanced Services at Cisco, supporting top financial customers with network design and applying best practices She was formerly a senior customer support engineer for the Routing Protocols Technical Assistance Center (TAC) team troubleshooting issues related to CEF and routing protocols Nakia has been with Cisco for more than six years, previously serving as a technical leader for the Architecture TAC team Russ White, CCIE No 2635, is a Principle Engineer in the Routing Protocol Design and Architecture team at Cisco He is a member of the IETF Routing Area Directorate, co-chair of the Routing Protocols Security Working Group in the IETF, a regular speaker at Cisco Networkers, a member of the CCIE Content Advisory Group, and the coauthor of six other books about routing and routing protocols, including Optimal Routing Design from Cisco Press Russ primarily works in the development of new features and design architectures for routing protocols Stacia McKee is a customer support engineer and technical leader of the Routing Protocols Technical Assistance Center (TAC) team This team focuses on providing post-sales support of IP routing protocols, MPLS, QoS, IP multicast, and many other Layer 3 technologies Stacia has been with Cisco for more than six years, previously serving as a technical leader of the Architecture TAC team and a member of the WAN/Access TAC team Learn the key features of packet-switching architectures Understand the basics of the CEF architecture and operation Examine the enhanced CEF structure, which improves scalability Learn how to troubleshoot in software-switching environments Understand the effect of CEF on a Cisco Catalyst 6500 Supervisor 720 Configure and troubleshoot load sharing with CEF Evaluate the effect of CEF in an MPLS VPN environment Review CEF design considerations that impact scalability Part I Understanding, Configuring, and Troubleshooting CEF Chapter 1 Introduction to Packet-Switching Architectures Chapter 2 Understanding Cisco Express Forwarding Chapter 3 CEF Enhanced Scalability Chapter 4 Basic IP Connectivity and CEF Troubleshooting Part II CEF Case Studies Chapter 5 Understanding Packet Switching on the Cisco Catalyst 6500 Supervisor 720 Chapter 6 Load Sharing with CEF Chapter 7 Understanding CEF in an MPLS VPN Environment Part III Appendix Appendix A Scalability This book is part of the Networking Technology Series from Cisco Press®, which offers networking professionals valuable information for constructing efficient networks, understanding new technologies, and building successful careers Category: Networking Covers: Routing and Switching 1587052369 Cisco Express Forwarding by Nakia Stringfield - CCIE No 13451; Russ White CCIE No 2635; Stacia McKee Publisher: Cisco Press Pub Date: April 24, 2007 Print ISBN-10: 1-58705-236-9 Print ISBN-13: 978-1-58705-236-1 Pages: 288 Table of Contents | Index Copyright About the Authors About the Technical Reviewers Acknowledgments Icons Used in This Book Command Syntax Conventions Introduction Goals and Methods Who Should Read This Book How This Book Is Organized The Future of CEF and Packet Switching Part I: Understanding, Configuring, and Troubleshooting CEF Chapter 1 Introduction to Packet-Switching Architectures Routing and Switching Understanding Router Pieces and Parts Cisco IOS Software: The Brains Processes and Scheduling Putting the Pieces Together: Switching a Packet Hardware and Software show Commands Summary Chapter 2 Understanding Cisco Express Forwarding Evolving Packet-Switching Methods CEF Tables CEF Table Entries Special Adjacencies Switching a Packet with CEF The CEF Epoch Configuring CEF/dCEF Summary References Chapter 3 CEF Enhanced Scalability Fundamental Changes to CEF for CSSR Changes to show Commands New show ip cef Commands New show cef Commands CEF Event Logger CEF Consistency Checker New CEF Processes Summary Chapter 4 Basic IP Connectivity and CEF Troubleshooting Troubleshooting IP Connectivity Troubleshooting Punt Adjacencies Understanding CEF Error Messages Troubleshooting Commands Reference Summary References Part II: CEF Case Studies Chapter 5 Understanding Packet Switching on the Cisco Catalyst 6500 Supervisor 720 CEF Switching Architecture on the Cisco Catalyst 6500 Troubleshooting CEF on the Catalyst 6500 SUP720 Platforms Summary References Chapter 6 Load Sharing with CEF Benefits of Load Sharing Load Sharing with Process Switching and Fast Switching Comparing CEF Per-Packet and CEF Per-Destination Load Sharing CEF Architecture and Load Sharing CEF Load Sharing Across Parallel Paths Per-Packet Load Sharing on Hardware-Based Platforms CEF Per-Packet Load Sharing on the Cisco GSR Platform CEF Load-Sharing Troubleshooting Examples Summary References Chapter 7 Understanding CEF in an MPLS VPN Environment An Internet Service Provider's Simple MPLS VPN Design Understanding the CEF and MPLS VPN Relationship CEF Considerations When Troubleshooting MPLS VPN Across Various Platforms CEF and MPLS VPN Load-Sharing Considerations Summary References Part III: Appendix Appendix A Scalability Memory Considerations Fast Convergence References Index Copyright Cisco Express Forwarding Nakia Stringfield, Russ White, Stacia McKee Copyright© 2007 Cisco Systems, Inc Published by: Cisco Press 800 East 96th Street Indianapolis, IN 46240 USA All rights reserved No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 First Printing March 2007 ISBN-13: 978-15870-5236-1 Library of Congress Cataloging-in-Publication Number: 2004117877 Warning and Disclaimer This book is designed to provide information about Cisco Express Forwarding (CEF) Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied The information is provided on an "as is" basis The authors, Cisco Press, and Cisco Systems, Inc., shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the discs or programs that may accompany it The opinions expressed in this book belong to the authors and are not necessarily those of Cisco Systems, Inc Trademark Acknowledgments All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized Cisco Press or Cisco Systems, Inc., cannot attest to the accuracy of this information Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark Feedback Information At Cisco Press, our goal is to create in-depth technical books of the highest quality and value Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community Readers' feedback is a natural continuation of this process If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through email at feedback@ciscopress.com Please make sure to include the book title and ISBN in your message We greatly appreciate your assistance Corporate and Government Sales Cisco Press offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales For more information please contact: U.S Corporate and Government Sales 1-800-382-3419 corpsales@pearsontechgroup.com For sales outside the U.S please contact: International Sales international@pearsoned.com Publisher Paul Boger Cisco Representative Anthony Wolfenden Cisco Press Program Manager Jeff Brady Associate Publisher David Dusthimer Executive Editor Brett Bartow Managing Editor Patrick Kanouse Development Editor Dayna Isley Senior Project Editor San Dee Phillips Copy Editor Written Elegance, Inc Technical Editors Neil Jarvis, LJ Wobker Team Coordinator Vanessa Evans Book and Cover Designer Louis Adair Composition Mark Shirar Indexer Tim Wright Proofreader Molly Proue Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] label disposition label imposition 2nd label swapping 2nd Layer 2 connectivity, troubleshooting Layer 2 header rewrite string Layer 3 switching LFIB (Label Forwarding Information Base) life cycle of processes line cards consistency checking process memory, verifying load distribution table load sharing benefits of CEF polarization in MPLS VPN environment between P and P devices CE multihomed to same PE platform dependencies site multihomed to different PEs troubleshooting lookups, longest match LSP (Label Switch Path)tunnels Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] managing buffer pools 2nd memory constraints on line cards, verifying process memory 4th memory management (Cisco IOS Software) memory pools memory regions packet buffers memory pools on Cisco IOS Software buffer pools, managing memory regions memory subregions packet buffers minimizing out-of-order packets mls ip cef load-sharing full command MPLS VPNs ISP networks label disposition label imposition 2nd label swapping 2nd LFIB LSP tunnels PE-CE load sharing between P and P devices CE multihomed to same PE platform dependencies site multihomed to different PEs troubleshooting debug commands on Cisco 10000 series routers on Cisco 12000 series routers on Cisco 6500 routers with Supervisor 2 on Cisco 6500 routers with Supervisor 720 on Cisco 7200 router with NPE-G2 on Cisco 7500 router show commands VRF tables mtries (multiway tries) performance stride patterns 2nd multiaccess network interface, FIB entries Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] new state (processes) not route adjacencies null adjacencies Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] out-of-order packets minimizing preventing output interface output queues overlapping prefixes, switching table design considerations overloaded links, troubleshooting CEF per-destination load-sharing Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] packet buffers packet switching during receive interrupt inbound packets on centralized switching routers with line cards on distributed switching platforms on shared media platforms packets, transmitting process switching required components bus backplane CPU interface processors memory switching fabric passive consistency checkers PE (provider edge)routers per-destination load sharing per-packet load sharing configuring on Cisco GSR platform on hardware-based platforms PFC3 (Policy Feature Card 3) physical connectivity, troubleshooting ping command 2nd platform dependencies for MPLS VPN load sharing point-to-point network interface, FIB entries preventing out-of-order packets priorities assigned to Cisco IOS Software private buffer pools process memory process scheduling process life cycle process priorities process switching 2nd processes scheduling special types of watchdog timer processor hogs process-switching packets public buffer pools punt adjacencies troubleshooting Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] ready state (processes) receive FIB entries receive interrupt receive rings recursive FIB entries recursive lookups regions, aliases remote login module command required components for packet switching bus backplane CPU interface processors memory switching fabric ring buffers routing broadcast domains collision domains packet switching bus backplane CPU memory required components switching fabric routing recursions routing tables, verifying Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] scalability, memory constraints Sched process scheduler scheduling processes SDRAM (synchronous dynamic random-access memory) shared media platforms, inbound packets shared memory architectures show adjacency command show adjacency detail command 2nd show arp command 2nd show buffers command 2nd 3rd show cef drop command show cef fib command show cef interface command 2nd show cef loadinfo command show cef memory command show cef not-cef-switched command show cef path command show cef state capabilities command show cef table command show cef table consistency-check command show cef timers command show commands, troubleshooting MPLS VPN show interfaces command 2nd 3rd show interfaces stat command show ip cache command show ip cef command 2nd 3rd 4th 5th 6th 7th 8th 9th show ip cef event command show ip cef interface command show ip cef internal command show ip cef summary command show ip cef switching statistics command show ip cef tree command show ip route command 2nd 3rd 4th 5th show ip route summary command show memory command 2nd show mls cef adjacency entry command show mls statistics command show monitor event-trace cef command show processes command 2nd show processes memory command 2nd show region command 2nd single-path failures, troubleshooting software-based CEF static buffer pools stride patterns 2nd structure of FIB subregions SUP720 (Supervisor 720) CEF, troubleshooting connectivity problems connectivity, verifying load sharing, troubleshooting PFC3 switching, required components bus backplane CPU interface processors memory switching fabric switching fabric bus backplane crossbar switching fabric shared memory architectures switching path, CEF modifications for CSSR switching tables, handling overlapping prefixes syntax for aliases Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] test cef enable command test cef table command traffic-share allocation transmit interrupt transmit rings transmitting packets during packet switching process troubleshooting CEF IP connectivity adjacency table, verifying ARP table, verifying CEF table, verifying issues, articulating Layer 2 issues network topology, scoping physical connectivity routing table, verifying load-sharing on SUP720 overloaded links MPLS VPN debug commands on Cisco 10000 series routers on Cisco 12000 series routers on Cisco 6500 routers with Supervisor 2 on Cisco 6500 routers with Supervisor 720 on Cisco 7200 routers with NPE-G2 on Cisco 7500 routers show commands on Catalyst 6500 SUP720 platform connectivity per-packet load sharing, performance issues punt adjacencies single-path failures TTIB (Toaster Tag FIB) tunnel algorithm Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] uncached adjacencies unresolved adjacencies Update Manager consistency checkers active passive Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] verifying adjacency table ARP table CEF table connectivity on SUP720 memory on line cards routing table VIPs (Versatile Interface Processors) VRF (virtual routing and forwarding) tables Index [SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W] watchdog timer ... Covers: Routing and Switching 1587052369 Cisco Express Forwarding by Nakia Stringfield - CCIE No 13451; Russ White CCIE No 2635; Stacia McKee Publisher: Cisco Press Pub Date: April 24, 2007 Print ISBN- 10: 1-58705-236-9... Registrar, Aironet, BPX, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco IOS, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Enterprise/Solver, EtherChannel, EtherFast, EtherSwitch, Fast... Murphy, Inside Cisco IOS Software Architecture, Indianapolis, Indiana: Cisco Press; 2000 Provides a detailed treatment of Cisco 7500 routers and Cisco 7200 routers Cisco, Parallel Express Forwarding on the Cisco 10000