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The comprehensive, hands-on guide for resolving IP routing problems
As the Internet continues to grow exponentially, the need for network engineers to build, maintain, and troubleshoot the growing number of component networks has also increased significantly. IP routing is at the core of Internet technology and expedient troubleshooting of IP routing failures is key to reducing network downtime and crucial for sustaining mission-critical applications carried over the Internet. Though troubleshooting skills are in great demand, few networking professionals possess the knowledge to identify and rectify networking problems quickly and efficiently. Troubleshooting IP Routing Protocols provides working solutions necessary for networking engineers who are pressured to acquire expert-level skills at a moment's notice. This book also serves as an additional study aid for CCIE candidates.
Authored by Cisco Systems engineers in the Cisco Technical Assistance Center (TAC) and the Internet Support Engineering Team who troubleshoot IP routing protocols on a daily basis, Troubleshooting IP Routing Protocols goes through a step-by-step process to solving real-world problems. Based on the authors' combined years of experience, this complete reference alternates between chapters that cover the key aspects of a given routing protocol and chapters that concentrate on the troubleshooting steps an engineer would take to resolve the most common routing problems related to a variety of routing protocols. The book provides extensive, practical coverage of BGP, IGRP, EIGRP, OSPF, IS-IS, multicasting, and RIP as run on Cisco IOS Software network devices.
Troubleshooting IP Routing Protocols offers you a full understanding of invaluable troubleshooting techniques that help keep your network operating at peak performance. Whether you are looking to hone your support skills or to prepare for the challenging CCIE exams, this essential reference shows you how to isolate and resolve common network failures and to sustain optimal network operation.
This book is part of the Cisco CCIE Professional Development Series, which offers expert-level instruction on network design, deployment, and support methodologies to help networking professionals manage complex networks and prepare for CCIE exams.
Troubleshooting Tips from Faraz Shamim, author of Troubleshooting IP Routing Protocols
1. Bring Stability in your Routing Protocols by using interface dampening
When interface state changes, both Routing table and Routing Protocols are notified. Unstable interface can cause excessive Routing table and Routing updates processing. This feature can be used to dampen the interface from the Routing table and Routing Protocols perspective. This is available for IP only. You can read more about it at cisco.com (CCO Login Required).
2. Reduce the number of OSPF updates over Frame-Relay link
With the help of flood reduction, OSPF updates can be reduced over the Frame-Relay links. The idea is to use the Demand Circuit capability over the Frame-Relay link. The layer 2 will stay up and the hellos will not be suppressed; only the LSA will not be refreshed over Frame-Relay link and it will not age out. This will reduce the amount of flooding over the frame-relay link. This feature was added in 12.1T and above.
3. Reduce the amount of flooding by choosing the right DR
You can reduce the amount of extra flooding when redistributing routes into OSPF. When routes are redistributed into OSPF, the router generates external LSAs into the OSPF database. Those external LSAs need to be flooded to every router on the segment. If you make this router, also a DR, then the type 5 LSA flooding can be reduced assuming the ASBR is sitting on the broadcast media.
4. Reduce the routing table size with totally stubby area
If there is only a single exit point in an area, then there is no need to carry any additional information about other areas. Extra information is only useful when you have more than one exit point outside the area. For single exit point use "area no-summary" so the ABR will not generate summary LSAs in that area. This can bring more scalability in that area.
5. Prevent accidental redistribution of routes into OSPF
If you are an ISP then it’s highly recommended to change all your area types into stub areas. Stub areas will prevent accidental redistribution into OSPF networks. The primary purpose of running IGP in an ISP network should be to carry next-hop information anyway, so redistribution should be avoided. Stub areas will provide extra security against any accidental redistribution in OSPF.
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Introduction.
1. Understanding IP Routing.
IP Addressing Concepts. IPv4 Address Classes. IPv4 Private Address Space. Subnetting and Variable-Length Subnet Masks. Classless Interdomain Routing. Static and Dynamic Routes. Dynamic Routing. Unicast Versus Multicast IP Routing. Classless Versus Classful IP Routing Protocols. Interior Gateway Protocols Versus Exterior Gateway Protocols. Distance Vector Versus Link-State Protocols. Distance Vector Routing Concepts. Link-State Protocols. Routing Protocol Administrative Distance. Fast Forwarding in Routers. Summary. Review Questions. References.
2. Understanding Routing Information Protocol (RIP).
Metric. Timers. Split Horizon. Split Horizon with Poison Reverse. RIP-1 Packet Format. RIP Behavior. RIP Rules for Sending Updates. RIP Rules for Receiving Updates. Example of Sending Updates. Example of Receiving Updates. Why RIP Doesn't Support Discontiguous Networks. Why RIP Doesn't Support Variable-Length Subnet Masking. Default Routes and RIP. Protocol Extension to RIP. Route Tag. Subnet Mask. Next Hop. Multicast Capability. Authentication. Compatibility Issues. Summary. Review Questions. Further Reading.
3.Troubleshooting RIP.
Flowcharts to Solve Common RIP Problems. Troubleshooting RIP Routes Installation. Problem: RIP Routes Not in the Routing Table. RIP Routes Not in the Routing Table-Cause: Missing or Incorrect network Statement. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Layer 1/2 Is Down. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: distribute-list in Is Blocking the Route. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Access List Blocking RIP Source. Address. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Access List Blocking RIP Broadcast or Multicast (in Case of RIP-2). Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Incompatible RIP Version Type. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Mismatch Authentication Key (RIP-2). Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Discontiguous Network. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Invalid Source. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Layer 2 Problem (Switch, Frame Relay, Other Layer 2 Media). Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Offset List Has a Large Metric Defined. Debugs and Verification. Solution. RIP Routes Not in the Routing Table-Cause: Routes Reached RIP Hop Count Limit. Debugs and Verification. Solution. Problem: RIP Is Not Installing All Possible Equal-Cost Paths-Cause: maximum-path Command Restricts RIP from Installing More Than One Path. Debugs and Verification. Solution. Troubleshooting RIP Routes Advertisement. Problem: Sender Is Not Advertising RIP Routes. Sender Is Not Advertising RIP Routes-Cause: Missing or Incorrect network Statement. Debugs and Verifications. Solution. Sender Is Not Advertising RIP Routes-Cause: Outgoing Interface Is Down. Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: distribute-list out Is Blocking the Route. Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: Advertised Network Interface Is Down. Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: Outgoing Interface Is Defined Passive. Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: Broken Multicast Capability (Frame Relay). Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: Misconfigured neighbor Statement. Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: Advertised Subnet Is VLSM. Debugs and Verification. Solution. Sender Is Not Advertising RIP Routes-Cause: Split Horizon Is Enabled. Debugs and Verification. Solution. Problem: Subnetted Routes Missing from the Routing Table of R2-Cause: Autosummarization Feature Is Enabled. Debugs and Verification. Solution. Troubleshooting Routes Summarization in RIP. Problem: RIP-2 Routing Table Is Huge-Cause: Autosummarization Is Off. Debugs and Verification. Solution. Problem: RIP-2 Routing Table Is Huge-Cause: ip summary-address Is Not Used. Debugs and Verification. Solution. Troubleshooting RIP Redistribution Problems. Debugs and Verification. Solution. Troubleshooting Dial-on-Demand Routing Issues in RIP. Problem: RIP Broadcast Is Keeping the ISDN Link Up-Cause: RIP Broadcasts Have Not Been Denied in the Interesting Traffic Definition. Debugs and Verification. Solution. Problem: RIP Updates Are Not Going Across the Dialer Interface-Cause: Missing broadcast Keyword in a dialer map Statement. Debugs and Verification. Solution. Troubleshooting Routes Flapping Problem in RIP. Debugs and Verification. Solution.
4. Understanding Interior Gateway Routing Protocol (IGRP).
Metrics. Timers. Split Horizon. Split Horizon with Poison Reverse. IGRP Packet Format. IGRP Behavior. Default Route and IGRP. Unequal-Cost Load Balancing in IGRP. Summary. Review Questions.
5. Troubleshooting IGRP.
Flowcharts to Solve Common IGRP Problems. Troubleshooting IGRP Route Installation. Problem: IGRP Routes Not in the Routing Table. IGRP Routes Not in the Routing Table-Cause: Missing or Incorrect network Statement. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Layer 1/2 Is Down. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: distribute-list in Is Blocking the Route. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Access List Blocking IGRP Source. Address. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Access List Blocking IGRP Broadcast. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Discontiguous Network. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Invalid Source. Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Layer 2 Problem (Switch, Frame Relay, Other Layer 2 Media). Debugs and Verification. Solution. IGRP Routes Not in the Routing Table-Cause: Sender's AS Mismatch. Debugs and Verification. Solution. Problem: IGRP Is Not Installing All Possible Equal-Cost Paths-Cause: maximum- paths Restricts IGRP to a Maximum of Four Paths by Default. Debugs and Verification. Solution. Troubleshooting IGRP Routes Advertisement. Problem: Sender Is Not Advertising IGRP Routes. Sender Is Not Advertising IGRP Routes-Cause: Missing or Incorrect network Statement. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Outgoing Interface Is Down. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: distribute-list out Is Blocking the Route. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Advertised Network Interface Is Down. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Outgoing Interface Is Defined as Passive. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Broken Broadcast Capability (Encapsulation Failure in Layer 2). Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Misconfigured neighbor Statement. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Advertised Subnet Is VLSM. Debugs and Verification. Solution. Sender Is Not Advertising IGRP Routes-Cause: Split Horizon Is Enabled. Debugs and Verification. Solution. Problem: Candidate Default Is Not Being Advertised-Cause: ip default-network Command Is Missing. Debugs and Verification. Solution. Troubleshooting IGRP Redistribution Problems. Problem: Redistributed Routes Are Not Getting Installed in the Routing Table-Cause: Metric Is Not Defined During Redistribution into IGRP. Debugs and Verification. Solution. Troubleshooting Dial-on-Demand Routing (DDR) Issues in IGRP. Problem: IGRP Broadcast Is Keeping the ISDN Link Up-Cause: IGRP Broadcasts Have Not Been Denied in the Interesting Traffic Definition. Debugs and Verification. Solution. Problem: IGRP Updates Are Not Going Across the Dialer Interface-Cause: Missing Broadcast Keyword in a dialer map Statement. Debugs and Verification. Solution. Troubleshooting Route Flapping Problem in IGRP. Problem: IGRP Routes Are Flapping-Cause: Packet Drops on Sender's or Receiver's Interface. Debugs and Verification. Solution. Troubleshooting Variance Problem. Problem: IGRP Not Using Unequal-Cost Path for Load Balancing-Cause: variance Command Is Missing or Misconfigured. Debugs and Verification. Solution.
6. Understanding Enhanced Interior Gateway Routing Protocol (EIGRP).
Metrics. EIGRP Neighbor Relationships. The Diffusing Update Algorithm. DUAL Finite-State Machine. EIGRP Reliable Transport Protocol. EIGRP Packet Format. EIGRP Behavior. EIGRP Summarization. EIGRP Query Process. Default Routes and EIGRP. Unequal-Cost Load Balancing in EIGRP. Summary. Review Questions.
7. Troubleshooting EIGRP.
Troubleshooting EIGRP Neighbor Relationships. Consulting the EIGRP Log for Neighbor Changes. EIGRP Neighbor Problem-Cause: Unidirectional Link. EIGRP Neighbor Problem-Cause: Uncommon Subnet. Misconfiguration of the IP Address on the Interfaces. Primary and Secondary IP Addresses of the Neighboring Interface Don't Match. Switch or Hub Between EIGRP Neighbor Connection Is Misconfigured or Is Leaking. Multicast Packets to Other Ports. EIGRP Neighbor Problem-Cause: Mismatched Masks. EIGRP Neighbor Problem-Cause: Mismatched K Values. EIGRP Neighbor Problem-Cause: Mismatched AS Number. EIGRP Neighbor Problem-Cause: Stuck in Active. Reviewing the EIGRP DUAL Process. Determining Active/Stuck in Active Routes with show ip eigrp topology active. Methodology for Troubleshooting the Stuck in Active Problem. Troubleshooting EIGRP Route Advertisement. EIGRP Is Not Advertising Routes to Neighbors When the Network Administrators Think That It Should. EIGRP Is Not Advertising Routes to Its Neighbors-Cause: Distribute List. EIGRP Is Not Advertising Routes to Its Neighbors-Cause: Discontiguous Networks. EIGRP Is Not Advertising Routes to Neighbors-Cause: Split-Horizon Issues. EIGRP Is Advertising Routes to Neighbors When the Network Administrators Think That It Shouldn't. EIGRP Is Advertising Routes with Unexpected Metric. Troubleshooting EIGRP Route Installation. EIGRP Is Not Installing Routes-Cause: Auto or Manual Summarization. EIGRP Is Not Installing Routes-Cause: Higher Administrative Distance. EIGRP Is Not Installing Routes-Cause: Duplicate Router Ids. Troubleshooting EIGRP Route Flapping. Troubleshooting EIGRP Route Summarization. EIGRP Summarization Route Problem-Cause: Subnetworks of Summary Route Don't Exist in Routing Table. EIGRP Summarization Route Problem-Cause: Too Much Summarization. Troubleshooting EIGRP Redistribution Problems. Troubleshooting EIGRP Dial Backup Problem. EIGRP Error Messages. Summary.
8. Understanding Open Shortest Path First (OSPF).
OSPF Packet Details. Hello Packets. Database Description Packets. Link-State Request Packets. Link-State Update Packets. Link-State Acknowledgment Packet. OSPF LSA Details. Router LSA. Router LSA Example. Network LSA. Network LSA Example. Summary LSA. Summary LSA Example. External LSA. External LSA Example. OSPF Areas. Normal Areas. Stub Areas. Totally Stubby Areas. Not-So-Stubby Areas. Type 7 LSAs. NSSA LSA Example. NSSA Configuration Example. Totally Not-So-Stubby Areas. Filtering in NSSA. Default Routes in NSSA. OSPF Media Types. Multiaccess Media. Point-to-Point Media. Nonbroadcast Multiaccess Media. Broadcast Model. Point-to-Point Model. Point-to-Multipoint Model. Demand Circuits. OSPF Media Type Summary. OSPF Adjacencies. OSPF Down State. OSPF Attempt State. OSPF Init State. OSPF 2-Way State. OSPF Exstart State. OSPF Exchange State. OSPF Loading State. OSPF Full State. Summary. Review Questions.
9. Troubleshooting OSPF.
Flowcharts to Solve Common OSPF Problems. Troubleshooting OSPF. Neighbor Relationships. Problem: OSPF Neighbor List Is Empty. OSPF Neighbor List Is Empty-Cause: OSPF Not Enabled on the Interface. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Layer 1/2 Is Down. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Interface Is Defined as Passive Under OSPF. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Access List Blocking OSPF Hellos on Both Sides. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Mismatched Subnet Number/Mask over a Broadcast Link. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Mismatched Hello/Dead Intervals. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Mismatched Authentication Type. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Mismatched Authentication Key. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Mismatched Area ID. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Mismatched Stub/Transit/NSSA Area Options. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: OSPF Adjacency Over Secondary IP Address. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: OSPF Adjacency over Asynchronous Interface. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: No Network Type or Neighbor Defined over NBMA. Debugs and Verification. Solution. OSPF Neighbor List Is Empty-Cause: Frame Relay/Dialer Interface Missing the broadcast Keyword on Both Sides. Debugs and Verification. Solution. Problem: OSPF Neighbor Stuck in ATTEMPT. OSPF Neighbor Stuck in ATTEMPT-Cause: Misconfigured neighbor Statement. Debugs and Verification. Solution. OSPF Neighbor Stuck in ATTEMPT-Cause: Unicast Connectivity Is Broken on NBMA. Debugs and Verification. Solution. Problem: OSPF Neighbor Stuck in INIT. OSPF Neighbor Stuck in INIT-Cause: Access List on One Side Is Blocking OSPF Hellos. Debugs and Verification. Solution. OSPF Neighbor Stuck in INIT-Cause: Multicast Capabilities Are Broken on One Side (6500 Switch Problem). Debugs and Verification. Solution. OSPF Neighbor Stuck in INIT-Cause: Cause: Authentication Is Enabled Only on One Side. Debugs and Verification. Solution. OSPF Neighbor Stuck in INIT-Cause: The frame-relay map/dialer-map Statement on One Side Is Missing the broadcast Keyword. Debugs and Verification. Solution. OSPF Neighbor Stuck in INIT-Cause: Hellos Are Getting Lost on One Side at Layer 2. Debugs and Verification. Solution. Problem: OSPF Neighbor Stuck in 2-WAY-Cause: Priority 0 Is Configured on All Routers. Debugs and Verification. Solution. Problem: OSPF Neighbor Stuck in EXSTART/EXCHANGE. OSPF Neighbor Stuck in EXSTART/EXCHANGE-Cause: Mismatched Interface MTU. Debugs and Verification. Solutions. OSPF Neighbor Stuck in EXSTART/EXCHANGE-Cause: Duplicate Router IDs on Neighbors. Debugs and Verification. Solution. OSPF Neighbor Stuck in EXSTART/EXCHANGE-Cause: Can't Ping Across with More Than Certain MTU Size. Debugs and Verification. Solution. OSPF Neighbor Stuck in EXSTART/EXCHANGE-Cause: Unicast Connectivity Is Broken. Debugs and Verification. Solutions. OSPF Neighbor Stuck in EXSTART/EXCHANGE-Cause: Network Type Is Point-to-Point Between PRI and BRI/Dialer. Debugs and Verification. Solution. Problem: OSPF Neighbor Stuck in LOADING. OSPF Neighbor Stuck in LOADING-Cause: Mismatched MTU Size. Debugs and Verification. Solution. OSPF Neighbor Stuck in LOADING-Cause: Link-State Request Packet Is Corrupted. Debugs and Verification. Solution. Troubleshooting OSPF Route Advertisement. Problem: OSPF Neighbor Is Not Advertising Routes. OSPF Neighbor Is Not Advertising Routes-Cause: OSPF Not Enabled on the Interface That Is Supposed to Be Advertised. Debugs and Verification. Solution. OSPF Neighbor Is Not Advertising Routes-Cause: Advertising Interface Is Down. Debugs and Verification. Solution. OSPF Neighbor Is Not Advertising Routes-Cause: Secondary Interface Is in a Different Area Than the Primary Interface. Debugs and Verification. Solution. Problem: OSPF Neighbor (ABR) Not Advertising the Summary Route. OSPF Neighbor (ABR) Not Advertising the Summary Route-Cause: Area Is Configured as Totally Stubby Area. Debugs and Verification. Solution. OSPF Neighbor (ABR) Not Advertising the Summary Route-Cause: ABR Is Not Connected to Area 0. Debugs and Verification. Solution. OSPF Neighbor (ABR) Not Advertising the Summary Route-Cause: Discontiguous Area 0. Debugs and Verification. Solution. Problem: OSPF Neighbor Is Not Advertising External Routes. OSPF Neighbor Is Not Advertising External Routes-Cause: Area Is Configured as a Stub Area or NSSA. Debugs and Verification. Solution. OSPF Neighbor Is Not Advertising External Routes-Cause: NSSA ABR Not Translating Type 7 LSAs into Type 5 LSAs. Debugs and Verification. Solution. Problem: OSPF Neighbor Not Advertising Default Routes. OSPF Neighbor Not Advertising Default Routes-Cause: Missing default- information originate Commands. Debugs and Verification. Solution. OSPF Neighbor Not Advertising Default Routes-Cause: Default Route Missing from the Neighbor's Routing Table. Debugs and Verification. Solution. OSPF Neighbor Not Advertising Default Routes-Cause: Neighbor Trying to Inject a Default into a Stub Area. Debugs and Verification. Solution. OSPF Neighbor Not Advertising Default Routes-Cause: NSSA ABR/ASBR Not Originating Type 7 Default. Debugs and Verification. Solution. Troubleshooting OSPF Route Installation. Problem: OSPF Not Installing Any Routes in the Routing Table. OSPF Not Installing Any Routes in the Routing Table-Cause: Network Type Mismatch. Debugs and Verification. Solution. OSPF Not Installing Any Routes in the Routing Table-Cause: IP Addresses Are Flipped in Dual Serial-Connected Routers. Debugs and Verification. Solution. OSPF Not Installing Any Routes in the Routing Table-Cause: One Side Is a Numbered and the Other Side Is an Unnumbered Point-to-Point Link. Debugs and Verification. Solution. OSPF Not Installing Any Routes in the Routing Table-Cause: Distribute List Is Blocking the Route Installation. Debugs and Verification. Solution. OSPF Not Installing Any Routes in the Routing Table-Cause: Broken PVC in a Fully Meshed Frame Relay Network with Broadcast Network Type. Debugs and Verification. Solution. Problem: OSPF Not Installing External Routes in the Routing Table. OSPF Not Installing External Routes in the Routing Table-Cause: Forwarding Address Is Not Known Through the Intra-Area or Interarea Route. Debugs and Verification. Solution. OSPF Not Installing External Routes in the Routing Table-Cause: ABR Not Generating Type 4 Summary LSA. Debugs and Verification. Solution. Troubleshooting Redistribution Problems in OSPF. Problem: OSPF Neighbor Is Not Advertising External Routes. OSPF Neighbor Is Not Advertising External Routes-Cause: Subnets Keyword Missing from the ASBR Configuration. Debugs and Verification. Solution. OSPF Neighbor Is Not Advertising External Routes-Cause: distribute-list out Is Blocking the Routes. Debugs and Verification. Solution. Troubleshooting Route Summarization in OSPF. Problem: Router Is Not Summarizing Interarea Routes-Cause: area range Command Is Not Configured on ABR. Debugs and Verification. Solution. Problem: Router Is Not Summarizing External Routes-Cause: summary-address Command Is Not Configured on ASBR. Debugs and Verification. Solution. Troubleshooting CPUHOG Problems. Problem: CPUHOG Messages During Adjacency Formation-Cause: Router Is Not Running Packet-Pacing Code. Debugs and Verification. Solution. Problem: CPUHOG Messages During LSA Refresh Period-Cause: Router Is Not Running LSA Group-Pacing Code. Debugs and Verification. Solution. Troubleshooting Dial-on-Demand Routing Issues in OSPF. Problem: OSPF Hellos Are Bringing Up the Link-Cause: OSPF Hellos Are Permitted as Interesting Traffic. Debugs and Verification. Solution. Problem: Demand Circuit Keeps Bringing Up the Link. Demand Circuit Keeps Bringing Up the Link-Cause: A Link Flap in the Network. Debugs and Verification. Solution. Demand Circuit Keeps Bringing Up the Link-Cause: Network Type Defined as Broadcast. Debugs and Verification. Solution. Demand Circuit Keeps Bringing Up the Link-Cause: PPP Host Routes Are Getting Redistributed into the OSPF Database. Debugs and Verification. Solution. Demand Circuit Keeps Bringing Up the Link-Cause: One of the Routers Is Not Demand Circuit-Capable. Debugs and Verification. Solution. Troubleshooting SPF Calculation and Route Flapping. SPF Running Constantly-Cause: Interface Flap Within the Network. Debugs and Verification. Solution. SPF Running Constantly-Cause: Neighbor Flap Within the Network. Debugs and Verification. Solution. SPF Running Constantly-Cause: Duplicate Router ID. Debugs and Verification. Solution. Common OSPF Error Messages. "Unknown routing protocol" Error Message. OSPF: “Could not allocate router id” Error Message. “%OSPF-4-BADLSATYPE: Invalid lsa: Bad LSA type” Type 6 Error Message. “OSPF-4-ERRRCV” Error Message. Mismatched Area ID. Bad Checksum. OSPF Not Enabled on the Receiving Interface.
10. Understanding Intermediate System-to-Intermediate System (IS-IS).
IS-IS Protocol Overview. IS-IS Routing Protocol. IS-IS Protocol Concepts. IS-IS Nodes, Links, and Areas. Adjacencies. ES-IS Adjacencies. IS-IS Adjacencies. Hierarchical Routing. IS-IS Packets. Generic IS-IS Packet Format. IS-IS Metrics. IS-IS Authentication. ISO CLNP Addressing. NSAP Format. NSAP Examples. Guidelines for Defining NSAP Addresses. IS-IS Link-State Database. Overview of the IS-IS Link-State Database. Flooding and Database Synchronization. Shortest Path First (SPF) Algorithm and IS-IS Route Calculation. Configuring IS-IS for IP Routing. Configuring IS-IS on Point-to-Point Serial Links. show clns protocol Command. show clns neighbors detail Command. show clns interface Command. show isis topology Command. show isis database Command. ATM Configuration Examples. IP Default Route Advertisement. Route Redistribution. IP Route Summarization. Summary. Additional IS-IS Packet Information. IS-IS Packet Fields (Alphabetical Order). Hello Packets. Link-State Packets. Sequence Number Packets. Review Questions. Further Reading.
11. Troubleshooting IS-IS.
Troubleshooting IS-IS Adjacency Problems. Problem 1: Some or All of the Adjacencies Are Not Coming Up. Step 1: Checking for Link Failures. Step 2: Verifying Basic Configuration. Step 3: Checking for Mismatched Level 1 and Level 2 Interfaces. Step 4: Checking for Area Misconfiguration. Step 5: Checking for Misconfigured IP Subnets. Step 6: Check for Duplicate System Ids. Problem 2: Adjacency in INIT State. Mismatched MTU. IS-IS Hello Padding. Misconfigured Authentication. Problem 3: Only ES-IS Adjacency Instead of IS-IS Adjacency Formed. Troubleshooting IS-IS Routing Update Problems. Route Advertisement Problems. Local Routes Not Being Advertised to Remote. Solution Summary. Route Redistribution and Level 2-to-Level 1 Route-Leaking Problems. Route-Flapping Problem. Solution Summary. IS-IS Errors. CLNS ping and traceroute. Case Study: ISDN Configuration Problem. IS-IS Troubleshooting Command Summary. Summary.
12. Understanding Protocol Independent Multicast (PIM).
Fundamentals of IGMP Version 1, IGMP Version 2, and Reverse Path Forwarding. IGMP Version 1. IGMP Version 2. Multicast Forwarding (Reverse Path Forwarding). PIM Dense Mode. PIM Sparse Mode. IGMP and PIM Packet Format. IGMP Packet Format. PIM Packet/Message Formats. Summary. Review Questions.
13. Troubleshooting PIM.
Troubleshooting IGMP Joins. Solution to IGMP Join Problem. Troubleshooting PIM Dense Mode. Solution to PIM Dense Mode Problem. Troubleshooting PIM Sparse Mode. Solution to PIM Sparse Mode Problem. Summary.
14. Understanding Border Gateway Protocol Version 4 (BGP-4).
BGP-4 Protocol Specification and Functionality. Neighbor Relationships. External BGP Neighbor Relationships. Internal BGP Neighbor Relationships. Advertising Routes. Synchronization Rule. Receiving Routes. Policy Control. Policy Control Using BGP Attributes. LOCAL_PREF Attribute. MULTI_EXIT_DISC (MED) Attribute. AS_PATH Attribute. NEXT_HOP Attribute. ORIGIN Attribute. WEIGHT: Cisco Systems, Inc. Proprietary Attribute. Reading BGP Attributes from Cisco IOS Software Output. Use of Route Maps in Policy Control. Using the match ip address Command in a Route Map. Using the match community Command in a Route Map. Using the match as-path Command in a Route Map. Using the set as-path prepend Command in a Route Map. Using the set community Command in a Route Map. Using the set local-preference Command in a Route Map. Using the set metric Command in a Route Map. Using the set weight Command in a Route Map. Policy Control Using filter-list, distribute-list, prefix-list, Communities, and Outbound Route Filtering (ORF). Use of Filter Lists in Policy Control. Use of Distribute Lists in Policy Control. Use of Prefix Lists in Policy Control. Use of Communities in Policy Control. Use of Outbound Route Filtering in Policy Control. Route Dampening. Scaling IBGP in Large Networks-Route Reflectors and Confederations. Route Reflection. AS Confederations. Best-Path Calculation. Summary. Review Questions.
15. Troubleshooting BGP.
Flowcharts to Solve Common BGP Problems. show and debug Commands for BGP-Related Troubleshooting. show ip bgp prefix Command. show ip bgp summary Command. show ip bgp neighbor [address] Command. show ip bgp neighbors [address] [advertised-routes] Command. show ip bgp neighbors [routes] Command. debug ip bgp update [access-list] Command. Standard Access List Usage. Extended Access List Usage. debug ip bgp neighbor-ip-address updates [access-list] Command. Troubleshooting BGP Neighbor Relationships. Problem: Directly Connected External BGP Neighbors Not Initializing. Directly Connected External BGP Neighbors Not Coming Up-Cause: Layer 2 Is Down, Preventing Communication with Directly Connected BGP Neighbor. Debugs and Verification. Solution. Directly Connected External BGP Neighbors Not Coming Up-Cause: Incorrect Neighbor IP Address in BGP Configuration. Debugs and Verification. Solution. Problem: Nondirectly Connected External BGP Neighbors Not Coming Up. Nondirectly Connected External BGP Neighbors Not Coming Up-Cause: Route to the Nondirectly Connected Peer Address Is Missing from the Routing Table. Debugs and Verification. Solution. Nondirectly Connected External BGP Neighbors Not Coming Up-Cause: ebgp- multihop Command Is Missing in BGP Configuration. Debugs and Verification. Solution. Nondirectly Connected External BGP Neighbors Not Coming Up-Cause: update- source interface Command Is Missing. Debugs and Verification. Solution. Problem: Internal BGP Neighbors Not Coming Up. Problem: BGP Neighbors (External and Internal) Not Coming Up-Cause: Interface Access List Blocking BGP Packets. Debugs and Verification. Solution. Troubleshooting BGP Route Advertisement/Origination and Receiving. Problem: BGP Route Not Getting Originated. BGP Route Not Getting Originated-Cause: IP Routing Table Does Not Have a Matching Route. Debugs and Verification. Solution. BGP Route Not Getting Originated-Cause: Configuration Error. Debugs and Verification. Solution. BGP Route Not Getting Originated-Cause: BGP Is Autosummarizing to Classful/ Network Boundary. Debugs and Verification. Solution. Problem in Propagating/Originating BGP Route to IBGP/EBGP Neighbors-Cause: Misconfigured Filters. Debugs and Verification. Solution. Problem in Propagating BGP Route to IBGP Neighbor but Not to EBGP Neighbor- Cause: BGP Route Was from Another IBGP Speaker. Debugs and Verification. Solution. IBGP Full Mesh. Designing a Route-Reflector Model. Designing a Confederation Model. Problem in Propagating IBGP Route to IBGP/EBGP Neighbor-Cause: IBGP Route Was Not Synchronized. Debugs and Verification. Solution. Troubleshooting BGP Route Not Installing in Routing Table. Problem: IBGP-Learned Route Not Getting Installed in IP Routing Table. IBGP-Learned Route Not Getting Installed in IP Routing Table-Cause: IBGP Routes Are Not Synchronized. Debugs and Verification. Solution. IBGP-Learned Route Not Getting Installed in IP Routing Table-Cause: IBGP Next Hop Not Reachable. Debugs and Verification. Solution. Announce the EBGP Next Hop Through an IGP Using a Static Route or Redistribution. Change the Next Hop to an Internal Peering Address. Problem: EBGP-Learned Route Not Getting Installed in IP Routing Table. EBGP-Learned Route Not Getting Installed in IP Routing Table-Cause: BGP Routes Are Dampened. Debugs and Verification. Solution. EBGP-Learned Route Not Getting Installed in IP Routing Table-Cause: BGP Next Hop Not Reachable in Case of Multihop EBGP. Debugs and Verification. Solution. EBGP-Learned Route Not Getting Installed in the Routing Table-Cause: Multiexit Discriminator (MED) Value Is Infinite. Debugs and Verification. Troubleshooting BGP Route-Reflection Issues. Problem: Configuration Mistakes-Cause: Failed to Configure IBGP Neighbor as a Route-Reflector Client. Debugs and Verification. Solution. Problem: Route-Reflector Client Stores an Extra BGP Update-Cause: Client-to-Client Reflection. Debugs and Verification. Solution. Problem: Convergence Time Improvement for RR and Clients-Cause: Use of Peer Groups. Debugs and Verification. Solution. Problem: Loss of Redundancy Between Route Reflectors and Route-Reflector Client -Cause: Cluster List Check in RR Drops Redundant Route from Other RR. Debugs and Verification. Solution. Troubleshooting Outbound IP Traffic Flow Issues Because of BGP Policies. Problem: Multiple Exit Points Exist but Traffic Goes Out Through One or Few Exit Routers-Cause: BGP Policy Definition Causes Traffic to Exit from One Place. Solution. Problem: Traffic Takes a Different Interface from What Shows in Routing Table- Cause: Next Hop of the Route Is Reachable Through Another Path. Debugs and Verification. Solution. Problem: Multiple BGP Connections to the Same BGP Neighbor AS, but Traffic Goes Out Through Only One Connection-Cause: BGP Neighbor Is Influencing Outbound Traffic by Sending MED or Prepended AS_PATH. Solution. Request AS 110 to Send the Proper MED for Each Prefix. Don't Accept MED from AS 110. Manually Change LOCAL_PREFERENCE for P1, P2, and P3 at All the Exit Points X, Y, and Z. Problem: Asymmetrical Routing Occurs and Causes a Problem Especially When NAT and Time-Sensitive Applications Are Used-Cause: Outbound and Inbound Advertisement. Debugs and Verification. Solution. Troubleshooting Load-Balancing Scenarios in Small BGP Networks. Problem: Load Balancing and Managing Outbound Traffic from a Single Router When Dualhomed to Same ISP-Cause: BGP Installs Only One Best Path in the Routing Table. Debugs Verification. Solution. Problem: Load Balancing and Managing Outbound Traffic in an IBGP Network- Cause: By Default, IBGP in Cisco IOS Software Allows Only a Single Path to Get Installed in the Routing Table Even Though Multiple Equal BGP Paths Exist. Debugs and Verification. Solution. Troubleshooting Inbound IP Traffic Flow Issues Because of BGP Policies. Problem: Multiple Connections Exist to an AS, but All the Traffic Comes in Through One BGP Neighbor, X, in the same AS-Cause: Either BGP Neighbor at X Has a BGP Policy Configured to Make Itself Preferred over the Other Peering Points, or the Networks Are Advertised to Attract Traffic from Only X. Debugs and Verification. Case 1. Case 2. Solution. Problem: Multiple Connections Exist to Several BGP Neighbors, but Most of the Traffic from Internet to 100.100.100.0/24 Always Comes in Through One BGP Neighbor from AS 110-Cause: Route Advertisements for 100.100.100.0/24 in AS 109 Attract Internet Traffic Through That BGP Neighbor in AS 110. Solution. Troubleshooting BGP Best-Path Calculation Issues. Problem: Path with Lowest RID Is Not Chosen as Best. Debugs and Verification. Solution. Problem: Lowest MED Not Selected as Best Path. Debugs and Verification. Solution. Troubleshooting BGP Filtering. Problem: Standard Access List Fails to Capture Subnets. Debugs and Verification. Solution. Problem: Extended Access Lists Fails to Capture the Correct Masked Route. Debugs and Verification. Solution. Extended Access List Solution. Problem: AS_PATH Filtering Using Regular Expressions. Summary.
Answers to Review Questions.
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