- play_arrow Configuring IS-IS
- play_arrow Configuring a Basic IS-IS Network
- Understanding IS-IS Configuration
- Example: Configuring IS-IS
- Understanding IS-IS Areas to Divide an Autonomous System into Smaller Groups
- Example: Configuring a Multi-Level IS-IS Topology to Control Interarea Flooding
- Understanding IS-IS Designated Routers
- Configuring Designated Router Election Priority for IS-IS
- Configuring an ISO System Identifier for the Router
- Understanding Default Routes
- How to Configure Multiple Independent IGP Instances of IS-IS
- play_arrow Configuring IS-IS Authentication and Checksums
- Configuring IS-IS Authentication
- Configuring IS-IS Authentication Without Network-Wide Deployment
- Understanding Hitless Authentication Key Rollover for IS-IS
- Example: Configuring Hitless Authentication Key Rollover for IS-IS
- Understanding Checksums on IS-IS Interfaces for Error Checking
- Example: Enabling Packet Checksums on IS-IS Interfaces for Error Checking
- play_arrow Configuring IS-IS Routing Policy and Route Redistribution
- Understanding Routing Policies
- Understanding Backup Selection Policy for IS-IS Protocol
- Example: Configuring Backup Selection Policy for IS-IS Protocol
- Configuring Backup Selection Policy for the IS-IS Protocol
- Example: Redistributing OSPF Routes into IS-IS
- Example: Configuring IS-IS Route Leaking from a Level 2 Area to a Level 1 Area
- Handling of the IS-IS Binding SID S Flag and RFC 7794 Prefix Attribute Flags
- Understanding BGP Communities, Extended Communities, and Large Communities as Routing Policy Match Conditions
- Example: Configuring a Routing Policy to Redistribute BGP Routes with a Specific Community Tag into IS-IS
- IS-IS Extensions to Support Route Tagging
- Example: Configuring a Routing Policy to Prioritize IS-IS Routes
- Configuring Overloading of Stub Networks
- play_arrow Configuring IS-IS Bidirectional Forwarding Detection
- play_arrow Configuring IS-IS Flood Groups
- play_arrow Configuring IS-IS Multitopology Routing and IPv6 Support
- IS-IS Multicast Topologies Overview
- Example: Configuring IS-IS Multicast Topology
- Understanding Dual Stacking of IPv4 and IPv6 Unicast Addresses
- Example: Configuring IS-IS Dual Stacking of IPv4 and IPv6 Unicast Addresses
- Understanding IS-IS IPv4 and IPv6 Unicast Topologies
- Example: Configuring IS-IS IPv4 and IPv6 Unicast Topologies
- play_arrow Configuring IS-IS Link and Node Link Protection
- Understanding Loop-Free Alternate Routes for IS-IS
- Example: Configuring Node-Link Protection for IS-IS Routes in a Layer 3 VPN
- Understanding Remote LFA over LDP Tunnels in IS-IS Networks
- Configuring Remote LFA Backup over LDP Tunnels in an IS-IS Network
- Example: Configuring Remote LFA over LDP Tunnels in IS-IS Networks
- Understanding Weighted ECMP Traffic Distribution on One-Hop IS-IS Neighbors
- Example: Weighted ECMP Traffic Distribution on One-Hop IS-IS Neighbors
- play_arrow Configuring IS-IS Traffic Engineering
- IS-IS Extensions to Support Traffic Engineering
- Using Labeled-Switched Paths to Augment SPF to Compute IGP Shortcuts
- Example: Enabling IS-IS Traffic Engineering Support
- Understanding Forwarding Adjacencies
- Example: Advertising Label-Switched Paths into IS-IS
- Understanding Wide IS-IS Metrics for Traffic Engineering
- Example: Enabling Wide IS-IS Metrics for Traffic Engineering
- Understanding LDP-IGP Synchronization
- Example: Configuring Synchronization Between IS-IS and LDP
- Layer 2 Mapping for IS-IS
- Example: Configuring Layer 2 Mapping for IS-IS
- Understanding Source Packet Routing in Networking (SPRING)
- Understanding Adjacency Segments, Anycast Segments, and Configurable SRGB in SPRING
- Example: Configuring SRGB in Segment Routing for IS-IS
- Example: Configuring Anycast and Prefix Segments in SPRING for IS-IS to Increase Network Speed
- Configuring Segment Routing Global Blocks Label Ranges in SPRING for IS-IS Protocol
- Configuring Anycast and Prefix segments in SPRING for IS-IS Protocol
- Flexible Algorithms in IS-IS for Segment Routing Traffic Engineering
- Configuring Flexible Algorithm for Segment Routing Traffic Engineering
- Understanding Topology-Independent Loop-Free Alternate with Segment Routing for IS-IS
- Configuring Topology-Independent Loop-Free Alternate with Segment Routing for IS-IS
- Example: Configuring Topology Independent Loop-Free Alternate with Segment Routing for IS-IS
- Static Adjacency Segment Identifier for ISIS
- Understanding Segment Routing over RSVP Forwarding Adjacency in IS-IS
- Understanding IS-IS Microloop Avoidance
- How to Enable SRv6 Network Programming in IS-IS Networks
- Example: Configuring SRv6 Network Programming in IS-IS Networks
- How to Enable Link Delay Measurement and Advertising in IS-IS
- How to Enable Strict SPF SIDs and IGP Shortcut
- play_arrow Configuring IS-IS Scaling and Throttling
- Understanding Link-State PDU Throttling for IS-IS Interfaces
- Example: Configuring the Transmission Frequency for Link-State PDUs on IS-IS Interfaces
- Understanding the Transmission Frequency for CSNPs on IS-IS Interfaces
- Example: Configuring the Transmission Frequency for CSNP Packets on IS-IS Interfaces
- Understanding IS-IS Mesh Groups
- Example: Configuring Mesh Groups of IS-IS Interfaces
- play_arrow Configuring IS-IS CLNS
- play_arrow Configuring IS-IS on Logical Systems
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- play_arrow Monitoring and Troubleshooting Network Issues
- play_arrow Monitoring Networks
- play_arrow Troubleshooting Network Issues
- Working with Problems on Your Network
- Isolating a Broken Network Connection
- Identifying the Symptoms of a Broken Network Connection
- Isolating the Causes of a Network Problem
- Taking Appropriate Action for Resolving the Network Problem
- Evaluating the Solution to Check Whether the Network Problem Is Resolved
- play_arrow Troubleshooting IS-IS
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- play_arrow Configuration Statements and Operational Commands
IS-IS Fast Reroute Convergence
Subsecond service restoration is a key requirement for MPLS and native IP-based network service providers. There are many ways to achieve fast reroute with a sub-optimal next-hop to reach the destination, such as loop-free alternate and remote loop-free alternate. In these cases, IGP downloads the primary and backup next-hop beforehand in the forwarding information base (FIB). A packet forwarding engine (PFE) performs a local repair when the primary next-hop loses its reachability to a given destination. Since the PFE already has an alternative path to reach its destination, subsecond restoration is possible. If the destination is reachable through equal-cost multi-path (ECMP), only the primary path is downloaded to the FIB. If a few ECMP links go down below the required bandwidth for a destination, fast reroute convergence is not possible.
To resolve this, the best ECMP links are grouped as a unilist of primary next-hops to reach the destination, and the sub-optimal ECMP links are grouped as a unilist of backup next-hops to reach the destination. If the bandwidth of the primary next-hops falls below the desired bandwidth, the PFE does a local repair and switches traffic to backup unilist next-hops. This is yet another backup, where the backup path is computed and installed in FIB for ECMP paths. Here, a set of best ECMP links is grouped as primary next-hops to reach the destination, and a set of sub-optimal ECMP links is grouped as backup next-hops to reach the destination. If the bandwidth of the primary next-hops falls below the desired bandwidth due to link failure on the primary group, the PFE should perform a local repair and switch the traffic to backup next-hops.
In the following topology, R1 has three ECMP links to D1 via R2. R1 also has three sub-optimal ECMP links to D1 via R3 and R2. All ECMP links L1, L2, and L3 can be placed under one group; a primary group, and also group sub-optimal ECMP links L3, L4, and L5 under another group, a backup group.
IS-IS calculates the shortest path using the shortest-path-first (SPF) algorithm and downloads primary next-hops with appropriate weight in FIB. IS-IS also calculates backup next-hops and downloads them to FIB with appropriate weight.
Backup next-hop weight will always be greater than the primary next-hop weight. If a link from the primary group goes down, the PFE performs a local repair and modifies the weight of the next-hops. The PFE forwards traffic to the destination with the least weight next-hops to achieve sub-millisecond convergence. IS-IS runs SPF and comes up with a set of primary and backup next-hops. IS-IS then updates the FIB with the updated next hops. PFE resumes traffic forwarding on new next-hops without any traffic loss.
