ccna dis3 - chapter09 - troubleshoot an enterprise network_ppt [compatibility mode]

8/3/2019 CCNA Dis3 - Chapter09 - Troubleshoot an Enterprise Network_ppt [Compatibility Mode]

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Chapter 9 Troubleshoot an Enterprisenetwork


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Situation

Hc vin cng ngh thng tin Bach Khoa - Website: www.bkacad.com
http://www.bkacad.com/http://www.bkacad.com/


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Enterprise network requirements


Most enterprises rely on theirnetworks to provide consistentand reliable access to shared

resources Without a reliable network,many organizations loseaccess to customer databasesand accounting records that

employees need to performtheir daily activities.


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Large enterprises generally span many different time zones andhave employees, customers, and suppliers accessing theirnetwork around the clock. For these organizations, anydowntime is extremely costly.

Cause of network downtime Weather and natural disasters

Security breaches

Man-made disasters

Power surges

Virus attacks Equipment failure

Misconfiguration of devices

Lack of resources



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Hc vin cng ngh thng tin Bach Khoa - Website: www.bkacad.com 6

The three-layer hierarchical network design modelseparates the functionality of the various networking

devices and links. This separation ensures efficient

network performance.

Enterprise should have service level agreements(SLAs) with key suppliers.

An SLA clearly documents network expectations in

terms of level of service.


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To minimize this type ofdowntime requireswarrantees on all criticalpieces of equipment.

Warrantees provide for rapidreplacement of missioncritical components.

Business continuity plansprovide a detailed plan of

action in case of unexpectedman-made or naturaldisasters such as powerfailures or earthquakes.


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Monitoring and proactive maintenance

Several groups of tools are available for monitoringnetwork performance levels and gathering data. Thesetools include:

Network utilities

Packet sniffing toolsSNMP monitoring tools

Network monitoring tools, techniques, and programs relyon the availability of a complete set of accurate and currentnetwork documentation. This documentation includes:

Physical and logical topology diagrams

Configuration files of all network devices

A baseline performance level



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Use Ping, Tracert, packet sniffing.



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Packet sniffingtools monitor thetypes of traffic onvarious parts of thenetwork.

These tools mayalso be able toremedy thesituation before

network congestionbecomes critical.



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(SNMP) allows monitoring of individual devices on the network.SNMP-compliant devices use agents to monitor a number ofpredefined parameters for specific conditions.

These agents collect information and store it in a databaseknown as the management information base (MIB).



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9.1.2



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Troubleshooting and the Failure Domain


The security of the network and the resources that it housesmust always be the highest priority.

security concerns in the business continuity plan. The planincludes:

oDocumentation of potential problems

oDescription of the appropriatecourse of action in the event ofproblems

oDetails of the security policy of thecompany

oDetails of the security risks of theactions

Refer 9.1.3


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Troubleshooting and the Failure Domain



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Activity 9.1.3



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Troubleshooting process

When a problem occurs on an enterprise network,troubleshooting that problem quickly and efficiently is veryimportant to avoid extended periods of downtime. Manydifferent structured and unstructured problem-solvingtechniques are available to the network technician. These

include:

Top-down

Bottom-up

Divide-and-conquer

Trial-and-error

Substitution



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When a situation requires a more structured approach,most network personnel use a layered process based onthe OSI or TCP/IP models.

When approaching a problem situation, follow the genericproblem-solving model, regardless of the type oftroubleshooting technique used.

Define the problem

Gather facts

Deduce possibilities and alternatives

Design plan of action

Implement solution

Analyze results



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OSI model



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OSI Model



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OSI Model



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OSI Model



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Activity 9.1.4.3



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Troubleshooting basic switching


Switches are currently the mostcommonly used Access Layer

networking device.

The most common problems

with switches occur at thePhysical Layer

Ensure that the power LED is illuminated.

Ensure that the correct type of cable connects the end device to the

switch.

Reseat the cables at both the workstation and the switch end.

Check the configuration to ensure that the port is in a no shutdown

state.

Checking steps:


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Commands: qshow running-configqshow port-security interface interface_id

qshow mac-address-table

qclear mac-address-table dynamic

qshow interface interface_id


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Switching loops are another potential source ofconnectivity issues.

STP prevents bridging loops and broadcast storms Indicators that a loop is present in a network include:

Loss of connectivity to, from, and through affected networkregions

High CPU utilization on routers connected to affectedsegments

High link utilization up to 100%

High switch backplane utilization as compared to thebaseline utilization

Syslog messages indicating packet looping, constantaddress relearning, or MAC address flapping messages

Increasing number of output drops on many interfacesHc vin cng ngh thng tin Bach Khoa - Website: www.bkacad.com 29


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A loop develops when the switch does not receive BPDUsor is unable to process them. This problem could be dueto:

Misconfigurations

Defective transceivers

Hardware and cabling issues

Overloaded processors

STP does not always identify the best root bridge or rootports.

Troubleshoote STPqshow spanning-tree

qshow spanning-tree interface interface_id



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Activity 9.2.1.5



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Troubleshooting VLAN Configuration Issues

If the Physical Layer is functioning correctly and communicationis still not occurring between end devices, check the VLANconfiguration.qshow vlan id vlan_number t

qShow vlan

qShow vlan brief

qShow vlan id 101Refer 9.2.2.1

If inter-VLAN routing is required, verify the followingconfigurations:

One port from each VLAN connects into a router interface orsubinterface.

Both the switch port and the router interface are configuredwith trunking.

Both the switch and router interface are configured with thesame encapsulation.



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Verify the interface configuration


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Access Port: switch considers the connected networkdevice as non-switch (unable to understand BPDU).

Trunk port: switch consider the connected network deviceas switch/bridge (able to speak and read BPDU).

Native VLAN is assigned to an 802.1Q trunk port. An802.1Q trunk port supports traffic coming from manyVLANs (tagged traffic) as well as traffic that does not comefrom a VLAN (untagged traffic)

Management VLANs is any VLAN you configure to access

the management capabilities of a switch.The native VLAN and management VLAN are VLAN1 by default.

Refer 9.2.2.3




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Activity 9.2.2.4



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Troubleshooting VTP

VTP simplifies the distribution of VLAN information tomultiple switches in a domain. Switches that participate inVTP operate in one of three modes: server, client, ortransparent. Only the server adds, deletes, and modifiesVLAN information.

When troubleshooting VTP on a network, ensure that: All participating devices have the same VTP domain name.

Two VTP servers exist in every domain, in case one fails.

All servers have the same information.

The revision numbers are the same on all devices. All devices use the same VTP version.

qshow vtp status

qvtp version



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Troubleshooting VTP

qvtp password passwordqshow vtp password

Refer 9.2.3.2



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Activity 9.2.3.3



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RIP Issues

RIP is a fairly basic and simple protocol to configure Compatibility issues exist between RIPv1 and RIPv2. If the

RIP routes are not being advertised, check for the followingproblems:

Layer 1 or Layer 2 connectivity issues

Requirements for VLSM subnetting but using RIPv1

RIPv1 and RIPv2 routing configurations mismatched

Network statements missing or incorrect

Interface IP addressing incorrect

Outgoing interface is down

Advertised network interface is down

Passive interface misconfigurations



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RIP Issues



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Activity 9.3.1.3



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EIGRP Issues

Possible reasons why EIGRP may not be working are: Layer 1 or Layer 2 connectivity issues exist. An interface has incorrect addressing or subnet mask.

AS numbers on EIGRP routers are mismatched.

The wrong network or incorrect wildcard mask is specified in the

routing process. The link may be congested or down.

The outgoing interface is down.

The interface for an advertised network is down.



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EIGRP Issues



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Activity 9.3.2.3



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OSPF Issues

OSPF Troubleshooting Issues

Neighbors must be part of the same OSPF area.

Interfaces for neighbors must have compatible IP addresses andsubnet masks.

Routers in an area should have the same OSPF hello interval anddead interval.

The routers must advertise the correct networks for interfaces toparticipate in the OSPF process.

The appropriate wildcard masks must be used to advertise thecorrect IP address ranges.

Authentication must be correctly configured on routers for

communication to occur.q show ip ospf

q show ip ospf neighbor

q show ip ospf interface

q debug ip ospf events

q debug ip ospf packetHc vin cng ngh thng tin Bach Khoa - Website: www.bkacad.com 46


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OSPF Issues



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OSPF Issues



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9.3.3.2



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Route Redistribution Issues

Configuring a static default routeqip route 0.0.0.0 0.0.0.0 S0/0/0qdefault-information originate

qredistribute static


RIP


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EIGRP


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OSPF


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Troubleshooting WAN connectivity

The IP address configured on an interface and the statusof the port and line protocol is viewable with the command:

qshow ip interface brief



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the encapsulation in use on a serial line, use thecommand:qshow interfaces


PPP?


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The PPP process involves both the LCP and NCP phases.LCP establishes the link and verifies that it is of sufficientquality to bring up the Layer 3 protocols. NCP allows Layer3 traffic to move across the link.

When troubleshooting PPP connectivity, verify that: LCP phase is complete

Authentication has passed, if configured

NCP phase is complete

qshow interfaceqdebug ppp negotiation

qdebug ppp packet



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Commands are available that assist in troubleshooting PPP. Toshow the status of the LCP and NCP phase


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Display PPP packets transmitted during the startup phasewhere PPP options are negotiated


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Display real-time PPP packet flow, use:


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Activity 9.4.1.5



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Troubleshooting WAN Authentication



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Authentication can be either one-way or two-way. Forenhanced security, use two-way or mutual authentication.Two-way authentication requires that each end deviceauthenticate to the other.

The most common problem with authentication is eitherforgetting to configure an account for the remote router ormisconfiguring the username and password.qppp pap sent-username username password password

Debugging the authentication process provides a quick

method of determining what is wrong.q debug ppp authentication



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Activity 9.4.2.3



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Determining if an ACL is the Issue

ACLs add a level of complexity to troubleshooting networkissues. When networks or hosts become unreachable and ACLs

are in use, it is critical to determine if the ACL is theproblem.

Is an ACL applied to the problem router or interface?

Has it been applied recently?

Did the issue exist before the ACL was applied?

Is the ACL performing as expected?

Is the problem with all hosts connected to the interface or only

specific hosts?

Is the problem with all protocols being forwarded or only specificprotocols?

Are the networks appearing in the routing table as expected?



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Logging shows the effect that ACLs are having on variouspackets.



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To display all ACLs configured on the router, whetherapplied to an interface or not:q show access-lists

To clear the number of matches for each ACL statement:q clear access-list counters

To display the source and destination IP address for eachpacket received or sent by any interface on the router:q debug ip packet

If the packets are simply passing through and the ACL

does not block a packet from this IP address, no debugmessage is generated.



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9.5.1.3



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Activity 9.5.1.4



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ACL configuration and Placement Issues

If it appears that the ACL is the problem, there are severalissues to check.


Refer 9.5.2.1


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ACL configuration and Placement Issues



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Activity 9.5.2.3



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Summary

When troubleshooting a network, determine the scope ofthe problem and isolate issue to a specific failure domain The most common problems with switches occur at the

Physical Layer

Use debug commands to isolate problems, not to monitornormal network operation

The most common physical layer WIN problems are notspecifying a clock rate on the link or ussing the wrong typeof cables.



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ccna dis3 - chapter09 - troubleshoot an enterprise network_ppt [compatibility mode]

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