Computer Networks 6
Layer 3 troubleshooting
Halmstad University
Olga Torstensson
035-167575 olga.torstensson@ide.hh.se
© 2003, Cisco Systems, Inc. All rights reserved.
1
Network Layer Overview
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2
Interior IP Routing
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3
Troubleshooting Static Routes
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4
Troubleshooting Static Routes
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5
Debug ip routing
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6
Common Routing Problems
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7
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?
© 2003, Cisco Systems, Inc. All rights reserved.
8
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
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9
RIP
• Incompatible RIP Version Types
• Mismatched Authentication Key
• RIP Hop Count Limit
• Discontinuous Networks
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10
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
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11
Common EIGRP Errors
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12
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
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13
Troubleshooting OSPF - Neighbours
OSPF Neighbour state
• Down
• Attempt
• Init
Possible reason for stuck in state
• No info from neighbour
• Hello sent – no reply
• 1 side blocking hello packet
• 2Way
• Normal on broadcast
networks
• Exstart / Exchange
• Access list, MTU size
• Loading
• Neighbour sending bad
packet
• Full
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14
Troubleshooting OSPF
Adjacencies not coming up?
• Layer 2 down
• OSPF no enabled
• Passive interface used
• Mismatched subnets
• Mismatched Hellos/Dead interval
• Mismatched authentication
• Mismatched Area Ids
• Mismatched Area types
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15
Troubleshooting OSPF – missing routes
• Routing protocols
Redistribution
• Stub vs NSSA vs Totally stub
Default routes
Summarisation
• Route filters
access-lists
• Virtual Links
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16
OSPF Mismatched Parameters
• Mismatched Hellos/Dead interval
• Mismatched authentication
• Mismatched Area Ids
• Mismatched Area types
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17
External Route Installation Problems
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18
Route Summarisation Problems
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19
Troubleshooting OSPF
Big show’ & ‘Big D’ for OSPF
• show ip ospf database
•
show ip ospf neighbors
• show ip ospf interface
• show ip ospf
• show ip route
© 2003, Cisco Systems, Inc. All rights reserved.
• debug ip ospf adj
• debug ip ospf events
20
Common BGP Neighbour Problems
• Directly connected EBGP neighbours not
initializing
• Non-directly connected EBGP neighbours
not initializing
• IBGP neighbours not initializing
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21
Directly Connected
EBGP Neighbor Problems
• Directly connected EBGP neighbors not
initializing
Layer 2 is down
incorrect neighbor IP address
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22
Directly Connected
EBGP Session
AS109
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AS110
23
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
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24
Troubleshooting BGP
Big show’ & ‘Big D’ for BGP
• show ip bgp
• show ip bgp neighbors
• show ip bgp summary
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• debug ip bgp [ A.B.C.D |
dampening | events | in |
keepalives | out | updates |
vpnv4 ]
25
Documentation review
Define Problem
Gather Facts
Consider Possibilities
Troubleshooting
tools
'show ...'
'debug ...'
'logging ...'
Si
Si
Create Action Plan
Implement Action Plan
Observe results
No
Fixed ?
Yes
Problem
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Diagnosis
Document Process
How Resolved
26
Documentation review
Define Problem
Gather Facts
Consider Possibilities
Troubleshooting
tools
'show ...'
'debug ...'
'logging ...'
Si
Si
Create Action Plan
Implement Action Plan
Observe results
No
Fixed ?
Problem
RouterA - interface
S0/0 is shutdown
Yes
Diagnosis
sh ip interface brief
show running-config
show protocols
© 2003, Cisco Systems, Inc. All rights reserved.
Document Process
How Resolved
No shutdown on
interfaceS0/0.
27