1 © 2003, cisco systems, inc. all rights reserved. computer networks 6 layer 3 troubleshooting...
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1© 2003, Cisco Systems, Inc. All rights reserved.
Computer Networks 6 Layer 3 troubleshooting
Halmstad University
Olga Torstensson
035-167575 [email protected]
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
101010© 2003, Cisco Systems, Inc. All rights reserved.
RIP
• Incompatible RIP Version Types
• Mismatched Authentication Key
• RIP Hop Count Limit
• Discontinuous Networks
111111© 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
131313© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting EIGRP
‘‘Big show’ & ‘Big D’ for EIGRPBig show’ & ‘Big D’ for EIGRP sh ip eigrp neighbors [ as_number | interface ]sh ip eigrp neighbors [ as_number | interface ]
sh ip eigrp topology [as_number | active | sh ip eigrp topology [as_number | active | pending | summary ]pending | summary ]
show ip protocolsshow ip protocols
show ip routeshow ip route
debug ip eigrp debug ip eigrp
141414© 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 stateOSPF Neighbour state Possible reason for stuck in state Possible reason for stuck in state
151515© 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?Adjacencies not coming up?
161616© 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
171717© 2003, Cisco Systems, Inc. All rights reserved.
OSPF Mismatched Parameters
• Mismatched Hellos/Dead interval
• Mismatched authentication
• Mismatched Area Ids
• Mismatched Area types
202020© 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 OSPFBig show’ & ‘Big D’ for OSPF
212121© 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
222222© 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
242424© 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
252525© 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 BGPBig show’ & ‘Big D’ for BGP
262626© 2003, Cisco Systems, Inc. All rights reserved.
Documentation reviewDefine Problem
Gather Facts
Consider Possibilities
Create Action Plan
Implement Action Plan
Observe results
Fixed ?
Problem Diagnosis How Resolved
Document ProcessYesNo
Troubleshootingtools
'show ...''debug ...''logging ...' SiSi
272727© 2003, Cisco Systems, Inc. All rights reserved.
Documentation review
Define Problem
Gather Facts
Consider Possibilities
Create Action Plan
Implement Action Plan
Observe results
Fixed ?
Problem Diagnosis How Resolved
Document ProcessYesNo
Troubleshootingtools
'show ...''debug ...''logging ...' SiSi
RouterA - interfaceS0/0 is shutdown
sh ip interface briefshow running-configshow protocols
No shutdown oninterfaceS0/0.