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Effective Troubleshooting for Network Layer Protocols at Halmstad University

This guide provides a comprehensive overview of troubleshooting techniques for the Network Layer, focusing on IP routing issues. It covers common problems related to static routes, EIGRP, OSPF, and BGP, including mismatched parameters, neighbor initialization issues, and more. Key commands for diagnosing problems are discussed, along with steps to isolate and document symptoms effectively. Designed for students and professionals at Halmstad University, this resource enhances understanding of network troubleshooting and provides practical solutions to common challenges.

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Effective Troubleshooting for Network Layer Protocols at Halmstad University

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  1. Computer Networks 6 Layer 3 troubleshooting Halmstad University Olga Torstensson 035-167575 olga.torstensson@ide.hh.se

  2. Network Layer Overview

  3. Interior IP Routing

  4. Troubleshooting Static Routes

  5. Troubleshooting Static Routes

  6. Debug ip routing

  7. Common Routing Problems

  8. Isolating the Problem • The first step is to isolate the problem. • Identify and document the symptoms • Some of the things to consider include: • Has anything in the network changed recently? • Is there anyone currently working on the network infrastructure?

  9. Troubleshooting Commands Commands used in this example and some of the commands that can be used for other routing protocols include: • show ip interface • show ip interface brief • show ip eigrp interfaces • show ip ospf interface • debug ip routing • debug ip rip • debug ip igrp transactions • debug ip eigrp • debug isis adj packets • debug isis update-packets

  10. RIP • Incompatible RIP Version Types • Mismatched Authentication Key • RIP Hop Count Limit • Discontinuous Networks

  11. Troubleshooting EIGRP Mismatched K Values (K1 for bandwidth , K2 for load , K3 for delay , K4 for reliability, K5 for reliability) • Mismatched AS Numbers • Stuck in Active • Duplicate Router ID’s

  12. Common EIGRP Errors

  13. Troubleshooting EIGRP • ‘Big show’ & ‘Big D’ for EIGRP • sh ip eigrp neighbors [ as_number | interface ] • sh ip eigrp topology [as_number | active | pending | summary ] • show ip protocols • show ip route • debug ip eigrp

  14. Down Attempt Init 2Way Exstart / Exchange Loading Full No info from neighbour Hello sent – no reply 1 side blocking hello packet Normal on broadcast networks Access list, MTU size Neighbour sending bad packet Troubleshooting OSPF - Neighbours OSPF Neighbour state Possible reason for stuck in state

  15. Layer 2 down OSPF no enabled Passive interface used Mismatched subnets Mismatched Hellos/Dead interval Mismatched authentication Mismatched Area Ids Mismatched Area types Troubleshooting OSPF Adjacencies not coming up?

  16. Troubleshooting OSPF – missing routes • Routing protocols • Redistribution • Stub vs NSSA vs Totally stub • Default routes • Summarisation • Route filters • access-lists • Virtual Links

  17. OSPF Mismatched Parameters • Mismatched Hellos/Dead interval • Mismatched authentication • Mismatched Area Ids • Mismatched Area types

  18. External Route Installation Problems

  19. Route Summarisation Problems

  20. show ip ospf database show ip ospf neighbors show ip ospf interface show ip ospf show ip route debug ip ospf adj debug ip ospf events Troubleshooting OSPF Big show’ & ‘Big D’ for OSPF

  21. Common BGP Neighbour Problems • Directly connected EBGP neighbours not initializing • Non-directly connected EBGP neighbours not initializing • IBGP neighbours not initializing

  22. Directly Connected EBGP Neighbor Problems • Directly connected EBGP neighbors not initializing • Layer 2 is down • incorrect neighbor IP address

  23. Directly Connected EBGP Session AS110 AS109

  24. Nondirectly Connected • Common causes for nondirectly connected EBGP neighbors not initializing are: • route to the nondirectly connected peer address is missing from the routing table. • ebgp-multihop command is missing • update-source interface command is missing

  25. show ip bgp show ip bgp neighbors show ip bgp summary debug ip bgp [ A.B.C.D | dampening | events | in | keepalives | out | updates | vpnv4 ] Troubleshooting BGP Big show’ & ‘Big D’ for BGP

  26. Documentation review

  27. Documentation review

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