Cisco Express Forwarding (paperback)

<> Cisco Express Forwarding   Understanding and troubleshooting CEF in Cisco routers and switches   Nakia Stringfield, CCIE® 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 packet-switching 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, CCIE® 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

Table of Contents:
Part I Understanding, Configuring, and Troubleshooting CEF 3 Chapter 1 Introduction to Packet-Switching Architectures 5 Routing and Switching 5 Understanding Broadcast and Collision Domains 5 Layer 3 Switching 8 Understanding Router Pieces and Parts 9 Interface Processors 10 Central Processing Unit 11 Memory 11 Backplanes and Switching Fabrics 11 Cisco IOS Software: The Brains 17 Memory Management 17 Interaction with Interface Processors 28 Processes and Scheduling 28 Process Memory 28 Process Scheduling 29 Putting the Pieces Together: Switching a Packet 35 Getting the Packet off the Network Media 35 Switching the Packet 39 Transmitting the Packet 44 Hardware and Software show Commands 45 Summary 48 Chapter 2 Understanding Cisco Express Forwarding 51 Evolving Packet-Switching Methods 51 Process Switching 51 Fast Switching 52 What Is CEF? 53 CEF Tables 54 Forwarding Information Base (FIB) 54 The Adjacency Table 60 Relating the CEF Tables 61 CEF Table Entries 62 FIB Entries 62 Generic FIB Entries 67 Interface-Specific FIB Entries 68 FIB Entries Built for a Multiaccess Network Interface 68 FIB Entries Built on a Point-to-Point Network Interface 69 FIB Entries Built on a 31-Bit Prefix Network Interface 69 Special Adjacencies 69 Auto Adjacencies 70 Punt Adjacency 70 Glean Adjacency 71 Drop Adjacency 72 Discard Adjacency 73 Null Adjacency 73 No Route Adjacencies 74 Cached and Uncached Adjacencies 74 Unresolved Adjacency 75 Switching a Packet with CEF 75 The CEF Epoch 77 Configuring CEF/dCEF 77 Summary 78 References 79 Chapter 3 CEF Enhanced Scalability 81 Fundamental Changes to CEF for CSSR 82 Data Structures 82 Switching Path Changes 84 Changes to show Commands 86 show ip cef 86 show ip cef interface 86 show ip cef summary 87 show cef state capabilities 88 New show ip cef Commands 89 show ip cef tree 89 show ip cef internal 90 show ip cef switching statistics 91 New show cef Commands 91 CEF Event Logger 94 CEF Consistency Checker 97 Passive Checkers 97 Active Checkers 97 Consistency-Checking Process 98 New CEF Processes 100 FIB Manager 100 Adjacency Manager 100 Update Manager 100 Summary 101 Chapter 4 Basic IP Connectivity and CEF Troubleshooting 103 Troubleshooting IP Connectivity 103 Accurately Describe the Problem 104 Scoping the Network Topology 105 Reviewing the OSI Model for Troubleshooting 106 Verifying the ARP Table 108 Verifying the Routing Table 111 Troubleshooting the CEF FIB Table 116 Troubleshooting Punt Adjacencies 129 Understanding CEF Error Messages 131 Troubleshooting Commands Reference 131 Summary 133 References 133 Part II CEF Case Studies 135 Chapter 5 Understanding Packet Switching on the Cisco Catalyst 6500 Supervisor 720 137 CEF Switching Architecture on the Cisco Catalyst 6500 137 Understanding Software-Based CEF and Hardware-Based CEF 137 Centralized and Distributed Switching 138 Troubleshooting CEF on the Catalyst 6500 SUP720 Platforms 139 Simple Checking of Connectivity 139 Systematic Checking of Connectivity 141 Troubleshooting Load Sharing 148 Summary 149 References 149 Chapter 6 Load Sharing with CEF 163 Benefits of Load Sharing 163 Load Sharing with Process Switching and Fast Switching 164 Comparing CEF Per-Packet and CEF Per-Destination Load Sharing 168 Understanding Per-Destination Load Sharing 168 Understanding Per-Packet Load Sharing 169 CEF Architecture and Load Sharing 171 CEF Load Sharing Across Parallel Paths 173 CEF Per-Destination Example 173 CEF Per-Packet Example 180 Per-Packet Load Sharing on Hardware-Based Platforms 184 CEF Per-Packet Load Sharing on the Cisco GSR Platform 185 CEF Load-Sharing Troubleshooting Examples 186 CEF Per-Destination Load Sharing Overloading One Link 186 CEF Per-Packet Load Sharing Causing Performance Issues 198 Troubleshooting a Single-Path Failure with CEF Load Sharing 200 CEF Traffic-Share Allocation 202 CEF Polarization and Load-Sharing Algorithms 210 Summary 214 References 215 Chapter 7 Understanding CEF in an MPLS VPN Environment 217 An Internet Service Provider’s Simple MPLS VPN Design 217 Understanding the CEF and MPLS VPN Relationship 219 Case 1: Label Disposition 221 Case 2: Label Imposition 222 Case 3: Label Swapping 224 Troubleshooting an MPLS VPN 224 CEF Considerations When Troubleshooting MPLS VPN Across Various Platforms 225 Cisco 7200 Router with an NPE-G2 226 Cisco 7500 Router 226 Cisco Catalyst 6500 with a Supervisor 2 227 Catalyst 6500 with a Supervisor 720 3BXL 228 Cisco 12000 Series Router 231 Cisco 10000 Series Router 236 CEF and MPLS VPN Load-Sharing Considerations 237 PE-CE Load Sharing: CE Multihomed to Same PE 237 PE-CE Load Sharing: Site Multihomed to Different PEs 243 Load Sharing Between P and P Devices 252 CEF and MPLS VPN Load-Sharing Platform Dependencies 253 Summary 253 References 254 Part III Appendix 257 Appendix A Scalability 259

About the Author :
Nakia Stringfield, CCIE No. 13451, is a network consulting engineer for Advanced Services at Cisco in Research Triangle Park, North Carolina, 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. She has given training courses on CEF operation and troubleshooting for internal employees. Nakia also worked for a year with IBM Global Services LAN Support in Research Triangle Park, North Carolina. Nakia attended North Carolina State University and completed her bachelor of science degree in electrical engineering in 1996. She also earned a master of science in computer networking and computer engineering from North Carolina State University in 2000.   Russ White, CCIE No. 2635, is a member of the Routing Protocol Design and Architecture Team at Cisco, Research Triangle Park, North Carolina. He is a member of the Internet Engineering Task Force (IETF) Routing Area Directorate, a cochair of the Routing Protocols Security Working Group in the IETF, a regular speaker at Networkers, a member of the Cisco Certified Internetwork Expert (CCIE) Content Advisory Group, a member of the core team developing the new Cisco Design certification, a regular contributor to the Internet Protocol Journal, 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 (RP) Technical Assistance Center (TAC) team at Cisco in  research Triangle Park, North Carolina. This team focuses on providing postsales support of IP routing protocols, Multiprotocol Label Switching (MPLS), quality of service (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 member of the WAN/Access TAC team. She has created and presented training on packet switching, router architecture, and troubleshooting for internal employees. Stacia has also been a technical editor and reviewer of Cisco.com technical documentation, mainly in router and IOS architecture and IP routing protocols technologies. She works closely with the IP Routing and IP Services groups within the Cisco Network Software and Systems Technology Group (NSSTG) on customer problems and early field trials. In 2000, Stacia completed her bachelor of science degree in computer information systems, bachelor of science degree in business administration, and bachelor of arts degree in computer science at the College of Charleston in Charleston, South Carolina.