Computer Networks 6

hardsweetlipsNetworking and Communications

Oct 28, 2013 (3 years and 9 months ago)

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© 2003, Cisco Sy stems, Inc. All rights reserv ed.

Computer Networks 6

Layer 3 troubleshooting

Halmstad University

Olga Torstensson

035
-
167575
olga.torstensson@ide.hh.se


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Network Layer Overview

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Interior IP Routing

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Troubleshooting Static Routes

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Troubleshooting Static Routes

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Debug ip routing

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Common Routing Problems

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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?


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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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RIP


Incompatible RIP Version Types


Mismatched Authentication Key


RIP Hop Count Limit


Discontinuous Networks


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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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Common EIGRP Errors

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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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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

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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?

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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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OSPF Mismatched Parameters


Mismatched Hellos/Dead interval


Mismatched authentication


Mismatched Area Ids


Mismatched Area types


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External Route Installation Problems

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Route Summarisation Problems

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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

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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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Directly Connected


EBGP Neighbor Problems


Directly

connected
EBGP

neighbors not
initializing


Layer 2 is down

incorrect neighbor IP address

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Directly Connected

EBGP Session

AS109

AS110

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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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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

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Documentation review

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Documentation review