Fault-Tolerant IP and MPLS Networks

• Copyright 2005
• Edition: 1st

• Book
• ISBN-10: 1-58705-126-5
• ISBN-13: 978-1-58705-126-5

Design and deploy high availability IP and MPLS network architectures with this comprehensive guide

• Includes a detailed overview of the IP/MPLS forwarding and control plane protocols, including OSPF, IS-IS, LDP, BGP, and RSVP
• Analyze fault-tolerant IP/MPLS control plane architectures with the explanations in this book
• Develop a clear understanding of various high availability aspects of IP/MPLS networks
• Learn how to seamlessly deploy IP/MPLS control plane restart mechanisms
• Master the application of fault-tolerant control-plane architectures in designing and deploying highly reliable and available MPLS applications, such as traffic engineering, L2VPNs, and L3VPNs
• Understand the layered architecture of network-level fault recovery mechanisms, such as optical, SONET, MPLS, and interactions between different layers

In the wake of increased traffic, today's service providers and enterprises must assure high availability across a variety of networked services and applications. Multiprotocol Label Switching (MPLS) is the enabling technology for the widespread deployment of IP networks in core and Metro Ethernet applications. Many service providers need to move their legacy Layer 2 and Layer 3 services onto converged MPLS and IP-enabled networks, but high availability is a prerequisite for offering profitable carrier-class services. Although most carrier-class routers do provide an adequate level of hardware redundancy, control-plane software is still vulnerable to and, in many cases, the cause of router failures.

Fault-Tolerant IP and MPLS Networks provides you with an in-depth analysis of the mechanisms that improve the reliability and availability of IP and MPLS control plane components. The IP/MPLS control-plane architecture and all its restart mechanisms are explained with examples and deployment considerations.

This explanation of IP/MPLS control-plane architecture begins with a service view of the network, moves on to the node-level view by partitioning the network into its constituent network elements, and then advances to the component-level view to explore various techniques that can be used to improve the reliability and availability of each component. The top-down and example-oriented approach facilitates a solid understanding of the constituent components before moving on to more advanced MPLS applications involving multiple components.

Fault-Tolerant IP and MPLS Networks is your practical guide for understanding, designing, and deploying carrier class IP/MPLS networks.

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.

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Understanding High Availability of IP and MPLS Networks

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Table of Contents

Introduction.

I. IP/MPLS FORWARDING PLAN.

1. Understanding High Availability of IP and MPLS Networks.

    Reliability and Availability of Converged Networks.

    Defining Key Terms.

      Availability and Unavailability.

      Reliability and Its Relationship to Availability.

      Fault Tolerance and Its Effect on Availability.

    MPLS Network Components.

    Network and Service Outages.

      Planned and Unplanned Outages.

      Main Causes of Network Outages.

    Design Strategies for Network Survivability.

      Mitigating Node-Level Unplanned Hardware-Related Outages.

      Mitigating Node-Level Unplanned Software-Related Outages.

         Reducing Downtime Related to Unplanned Control-Plane Restart.

         Stateful Switchover and Nonstop Forwarding.

         Reducing Unplanned Downtime Using Component-Level Modularity and Restartability.

      Mitigating Node-Level Planned Outages.

      Mitigating Network Outages Against Link and Node Failures.

      Mitigating Network Outages via Effective Operation and Maintenance Mechanisms.

      Improving Network Security via Fault-Tolerance Mechanisms.

    Scope of the Book.

    References.

2. IP Forwarding Plane: Achieving Nonstop Forwarding.

    Overview of IP Forwarding.

      Classful Addressing.

      Classless Addressing.

      IP Address Lookup.

      Evolution of IP Forwarding Architectures.

      Route Cache-Based Centralized Forwarding Architecture.

      Distributed Forwarding Architectures.

      Cisco Express Forwarding.

    Separation of IP Control and Forwarding Planes.

      IP Control-Plane Stateful Switchover.

      IP Forwarding-Plane Nonstop Forwarding.

    IP Nonstop Forwarding Architecture.

      IP Control-Plane SSO.

      Separation of Control and Forwarding.

      Summary of IP Nonstop Forwarding Operations.

      IP SSO and NSF Capabilities in Cisco IOS Architecture.

    External View of the IP SSO and NSF.

    Summary.

    References.

3. MPLS Forwarding Plane: Achieving Nonstop Forwarding.

    Overview of MPLS.

      MPLS Label Lookup and Forwarding.

      Separation of MPLS Control and Forwarding Planes.

      MPLS Applications.

    MPLS Forwarding Architecture.

      MPLS Control-Plane Stateful Switchover.

      MPLS Forwarding-Plane Nonstop Forwarding.

    MPLS Nonstop Forwarding Architecture.

    External View of the MPLS SSO and NSF.

    Summary.

    References.

II. IP/MPLS CONTROL PLANE.

4. Intradomain IP Control Plane: Restarting OSPF Gracefully.

    Internet Routing Architecture.

      OSPF Control- and Forwarding-Plane Components.

      OSPF Control-Plane Restart Approaches.

    Understanding the Detrimental Effects of the OSPF Restart.

    Overview of OSPF Routing.

      OSPF Hierarchical Routing.

      Establishing Adjacencies and Synchronizing Link-State Databases.

      OSPF Link-State Advertisements.

    Mitigating the Detrimental Effects of OSPF Restart.

      OSPF Restart Mechanisms.

      OSPF Restart Signaling Mechanism.

         Modifications to the OSPF Hello Processing Procedure.

         Link-State Database Resynchronization.

         Restarting Router Behavior.

         SPF Calculations.

         Nonrestarting Router (Helper-Node) Behavior.

         Operation of the OSPF Restart Signaling Mechanism.

      OSPF Graceful Restart Mechanism.

         Reliable Delivery of the Grace LSAs on Unplanned and Planned Restart.

         Restarting a Router’s Behavior.

         Helper Node’s Behavior.

    Operation of the OSPF Graceful Restart Mechanism.

    Comparison of the OSPF Restart Mechanisms.

    Network Deployment Considerations.

      Scenario 1: R1 and R2 Are Restart Signaling/NSF-Capable.

      Scenario 2: R1 Is Restart Signaling- and NSF-Capable, but R3 Is Only Restart Signaling-Capable.

      Scenario 3: R1 Is Restart Signaling- and NSF-Capable, but R4 Is Restart Signaling- and NSF-Incapable.

      Scenario 4: R1 Is Restart Signaling- and NSF-Capable, and R5 Is Graceful Restart- and NSF-Capable.

    Summary.

    References.

5. INTRADOMAIN IP CONTROL PLANE: RESTARTING IS-IS GRACEFULLY.

    Understanding the Detrimental Effects of the IS-IS Restart.

      Original IS-IS Restart Behavior.

      Negative Effects of the Original IS-IS Restart Behavior.

    Overview of IS-IS Routing.

         IS-IS Hierarchical Routing.

         Discovering Neighbors and Establishing Adjacencies.

         Establishing Adjacencies Using a Three-Way Handshake.

         Maintaining Adjacencies.

         Link-State Packets.

         LSP Databases.

         Synchronizing LSP Databases.

      Congestion Indication Through the Overload Bit.

      IS-IS Designated Router.

    Mitigating the Detrimental Effects of the IS-IS Restart.

      IS-IS Restart.

      IETF IS-IS Restart Mechanism.

         Restart TLV.

         Timers.

         Restarting Router (a Router with a Preserved FIB) Behavior.

         Nonrestarting Router (Helper Neighbor) Behavior.

         Starting Router (a Router Without a Preserved FIB) Behavior.

    IETF IS-IS Restart Operation.

      Starting Router Operation.

      Restarting Router Operation.

    Cisco IS-IS Restart.

    Cisco IS-IS Restart Operation.

    Comparison of the IS-IS Restart Mechanisms.

    Network Deployment Considerations.

      Scenario 1: R1 and R2 Are IETF IS-IS Restart- or NSF-Capable.

      Scenario 2: R1 Is IETF IS-IS Restart- or NSF-Capable, but R3 Is Only IETF IS-IS Restart-Capable.

      Scenario 3: R1 Is IETF IS-IS Restart- or NSF-Capable, but R4 Is IETF Restart- or NSF-Incapable.

      Scenario 4: R1 and R2 Are Cisco IS-IS Restart- or NSF-Capable.

      Scenario 5: R1 Is Cisco IS-IS Restart- or NSF-Capable and R3 Is Cisco IS-IS Restart- or NSF-Incapable.

    Summary.

    References.

6. Interdomain IP Control Plane: Restarting BGP Gracefully.

    Introduction to Border Gateway Protocol Routing.

      BGP Control- and Forwarding-Plane Components.

      Route Flaps Caused by BGP Control-Plane Restart.

      BGP Restart Process.

    BGP Routing Evolution and Concepts.

      BGP Messages.

      Idle and Established States.

      Exchange of Routing Information.

      Internal and External Speakers.

      BGP Path Attributes.

      AS_PATH and NEXT_HOP Attributes.

      Routing Information Bases of BGP Speakers.

      BGP Route-Selection Process.

      BGP Route Reflection.

    Mitigating the Detrimental Effects of the BGP Restart.

      BGP Graceful Restart Mechanism.

      Exchange of Graceful Restart Capability.

      BGP Graceful Restart Capability Format.

      Restarting BGP Speaker Behavior.

      Helper BGP Speaker Behavior.

      Operation of the BGP Graceful Restart Mechanism.

    Network-Deployment Considerations.

      Scenario 1: R1/R2 Are BGP Graceful Restart- and NSF-Capable.

      Scenario 2: R1 Is BGP Restart- and NSF-Capable, but R3 Is Only BGP Restart- Capable.

      Scenario 3: R1 Is BGP Graceful Restart- and NSF-Capable, but R4 Is BGP Graceful Restart- and NSF-Incapable.

    Summary.

    References.

7. MPLS Control Plane: Restarting BGP with MPLS Gracefully.

    MPLS Control- and Forwarding-Plane Components.

      MPLS Network Components.

      Layer 2 and Layer 3 Virtual Private Network Services.

      Forwarding Tables for Layer 2 and Layer 3 VPN Services.

      MPLS Forwarding State Entries.

    Detrimental Effects of BGP with MPLS Restart.

    Review of Chapter 6 Concepts.

    Overview of the BGP as MPLS Control Plane.

      BGP and MPLS Interrelationship.

      BGP Label-Distribution Mechanisms.

      Advertising Labeled BGP Routes.

      Advertising Labeled BGP Routes Through a Route Reflector.

      Withdrawing Labeled BGP Routes.

    Mitigating the Detrimental Effects of BGP with MPLS Restart.

      BGP with MPLS Graceful Restart Mechanism.

      Behavior of a Restarting LSR.

      Behavior of Helper LSRs.

    BGP/MPLS Graceful Restart Operation.

    Network-Deployment Considerations.

      Scenario 1: LSR1 and LSR2 Are Capable of Both BGP with MPLS Graceful Restart and of NSF.

      Scenario 2: LSR1 Is Capable of Both BGP with MPLS Graceful Restart and of NSF, but LSR3 Is Capable Only of BGP with MPLS Graceful Restart.

      Scenario 3: LSR1 Is BGP with MPLS Graceful Restart- and NSF- Capable, but LSR4 Is Both BGP with MPLS Graceful Restart- and NSF- Incapable.

    Summary.

    References.

8. MPLS Control Plane: Restarting LDP Gracefully.

    Overview of LDP.

      LDP FEC-to-LSP Association.

      LDP Peers.

      Hello Adjacency Establishment.

      Hello Adjacency Maintenance.

      LDP Messages.

      Label Distribution Control Mode (Ordered Versus Independent).

      Label Advertisement Mode (Unsolicited Versus On Demand).

          Downstream On Demand.

         Downstream Unsolicited.

      Label Retention Mode (Liberal Versus Conservative).

      Interactions Between LIB, LFIB, and Routing.

      Establishing Pseudowires (PWs) Using LDP.

    LDP Control-Plane and Forwarding-Plane Components.

      LDP Forwarding State.

      LDP Control-Plane State.

    Understanding the Detrimental Effects of LDP Restart.

    Mitigating Detrimental Effects of the LDP Restart.

      Comparison of LDP Restart Methods.

    LDP GR Mechanism for Downstream Unsolicited Mode.

      Initial Capability Exchange.

      LDP Session Failure.

      LDP Session Reestablishment and State Recovery.

      Nonrestarting LSR Behavior.

      Restarting LSR Behavior.

    LDP GR Operation in Downstream Unsolicited Mode.

      Option A: LDP GR Operation for Downstream Unsolicited Mode.

      Option B: LDP GR Operation for Downstream Unsolicited Mode.

    LDP GR Mechanism for Downstream On-Demand Mode.

      LDP GR Common Procedures.

      Downstream On-Demand Specific LDP GR Procedures.

         Restarting LSR Behavior for Ingress LSRs.

         Restarting LSR Behavior for Egress LSRs.

         Restarting LSR Behavior for Transit LSRs.

         Nonrestarting LSR Behavior for Ingress Neighbors.

         Nonrestarting LSR Behavior for Egress Neighbors.

         Nonrestarting LSR Behavior for Transit Neighbors.

    Comparison of LDP GR Mechanisms for Downstream Unsolicited and Downstream On-Demand Modes.

    Network Deployment Considerations.

      Scenario 1: LSR1 and LSR2 Are LDP GR- and NSF-Capable.

      Scenario 2: LSR1 Is LDP GR- and NSF-Capable, but LSR3 Is Only LDP GR- Capable.

      Scenario 3: LSR1 Is LDP GR- and NSF-Capable, but LSR4 Is LDP GR- and NSF-Incapable.

    Summary.

    References.

9. MPLS Control Plane: Restarting RSVP-TE Gracefully.

    Motivations for Traffic Engineering.

      Traffic-Engineering Capabilities.

      MPLS Traffic Engineering.

    Overview of RSVP.

      Path Message.

      Path State Block.

      Resv Message.

      Reservation State Block.

      Soft State.

      Using RSVP in MPLS-TE.

      Generalization of the Flow Concept.

      LSP Tunnel.

      LSP_TUNNEL Objects.

      SESSION_ATTRIBUTE Object.

      Specifying ERO.

      RECORD_ROUTE Object.

      RSVP-TE Soft State.

      Lifetime of RSVP-TE State.

         Detecting RSVP-TE Failures.

    RSVP-TE Control-Plane and Forwarding-Plane Components.

      Detrimental Effects of RSVP-TE Restart.

      Term Definitions.

    Mitigating the Detrimental Effects of RSVP-TE Restart.

      RSVP-TE GR Mechanism.

         Initial Capability Exchange.

         RSVP-TE Control-Plane Restart.

         Reestablishment of Hello Communication.

      Restarting LSR Behavior.

         Head-End Restarting.

         Midpoint Restarting.

         Tail-End Restarting.

      Nonrestarting Neighbor Behavior.

    RSVP-TE Graceful Restart Operation.

    Network Deployment Considerations for RSVP-TE Graceful Restart.

      Scenario 1: LSR1 and LSR2 Are RSVP-TE GR- and NSF-Capable.

      Scenario 2: LSR1 Is RSVP-TE GR- and NSF-Capable, but LSR3 Is Only RSVP-TE GR-Capable.

      Scenario 3: LSR1 Is RSVP-TE GR- and NSF-Capable, but LSR4 Is RSVP-TE GR- and NSF-Incapable.

     Summary.

    References.

III. HIGH AVAILABILITY OF MPLS-BASED SERVICES.

10. Improving the Survivability of IP and MPLS Networks.

    Layer 2 and Layer 3 Services over MPLS Networks.

      Provider-Provisioned Virtual Private Networks.

      VPN Tunnels.

         Tunnel Demultiplexing.

         Signaling of the Tunnel Labels and VPN Labels.

      Service Attributes Related to Network Availability.

      Network Fault-Tolerance Techniques.

    MPLS Traffic Engineering.

      MPLS-TE Functional Modules.

      Establishment of an MPLS-TE Tunnel.

      MPLS-TE Tunnel Reoptimization.

      Protecting MPLS-TE Tunnels Against Control-Plane Failures.

         Intra-Area MPLS Traffic Engineering.

         Inter-Area or Intra-AS MPLS Traffic Engineering.

         Inter-AS MPLS Traffic Engineering.

    Layer 3 Virtual Private Networks.

      CE-Based L3VPNs.

      PE-Based L3VPNs.

         PE-Based L3VPN Reference Model.

         VPN Routing and Forwarding Tables.

         PE-to-PE Tunnel.

         Distribution of L3VPN Labels.

         IPv6-Based L3VPN Services.

      Protecting L3VPN Service Against Control-Plane Failures.

         Single-AS MPLS Backbone.

         Multi-AS MPLS Backbone.

         Carrier Supporting Carrier (CSC).

    Layer 2 Virtual Private Networks.

      Protecting L2VPN Services Against Control-Plane Failures.

      Virtual Private Wire Service.

      Virtual Private LAN Service.

    Network Fault Tolerance and MPLS-Based Recovery.

      Protection and Restoration.

      Optical Layer Protection.

      SONET/SDH Layer Protection.

      IP Layer Restoration.

      MPLS Layer Protection–Fast ReRoute.

      Protecting Bypass Tunnels Against Control-Plane Failures.

      Interactions Between Different Protection Layers.

    Network Fault Tolerance and MPLS OAM Mechanisms.

      Bidirectional Forwarding Detection.

      Motivations.

         How Does BFD Improve Network Availability?

         How Does BFD Improve Network Convergence?

      BFD Protocol Mechanics.

      BFD Applications.

         Using BFD for Detecting IGP Neighbor Liveness.

         Using BFD for LSP Data-Plane Fault Detection and Control-Plane Verification.

         Using BFD for PW Fault Detection.

         Using BFD for MPLS FRR Fault Detection.

         Using BFD for Fault Detection in the Access Network.

      BFD Interactions with the IP and MPLS Control-Plane Graceful Restart Mechanisms.

    Network Fault Tolerance and In-Service Software Upgrades.

    Summary.

    References.

Index.

Index

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