1 © 2003, Cisco Systems, Inc. All rights reserved. Computer Networks 6 Layer 3 troubleshooting Halmstad University Olga Torstensson

222 © 2003, Cisco Systems, Inc. All rights reserved. Network Layer Overview

333 © 2003, Cisco Systems, Inc. All rights reserved. Interior IP Routing

444 © 2003, Cisco Systems, Inc. All rights reserved. Troubleshooting Static Routes

555 © 2003, Cisco Systems, Inc. All rights reserved. Troubleshooting Static Routes

666 © 2003, Cisco Systems, Inc. All rights reserved. Debug ip routing

777 © 2003, Cisco Systems, Inc. All rights reserved. Common Routing Problems

888 © 2003, Cisco Systems, Inc. All rights reserved. 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?

999 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. RIP Incompatible RIP Version Types Mismatched Authentication Key RIP Hop Count Limit Discontinuous Networks

11 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. Common EIGRP Errors

13 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. Troubleshooting OSPF – missing routes Routing protocols Redistribution Stub vs NSSA vs Totally stub Default routes Summarisation Route filters access-lists Virtual Links

17 © 2003, Cisco Systems, Inc. All rights reserved. OSPF Mismatched Parameters Mismatched Hellos/Dead interval Mismatched authentication Mismatched Area Ids Mismatched Area types

18 © 2003, Cisco Systems, Inc. All rights reserved. External Route Installation Problems

19 © 2003, Cisco Systems, Inc. All rights reserved. Route Summarisation Problems

20 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. Common BGP Neighbour Problems Directly connected EBGP neighbours not initializing Non-directly connected EBGP neighbours not initializing IBGP neighbours not initializing

22 © 2003, Cisco Systems, Inc. All rights reserved. Directly Connected EBGP Neighbor Problems Directly connected EBGP neighbors not initializing Layer 2 is down incorrect neighbor IP address

23 © 2003, Cisco Systems, Inc. All rights reserved. Directly Connected EBGP Session AS109 AS110

24 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. Documentation review

27 © 2003, Cisco Systems, Inc. All rights reserved. Documentation review