All Cisco-Network Study Notes: Physical Band Troubleshooting

Physical Band Troubleshooting

The best accepted arrangement problems can be traced to cable problems. The afterward questions

will advice actuate whether there is a UTP cable problem.

• Are the cables the absolute blazon for this installation?

— Class 3 cabling can alone abutment 10BaseT. Was a Class 3 cable installed

instead of a class 5?

— For Class 5 cabling, was the cable installed correctly? Severe aeroembolism in a

Category 5 cable can account a 10/100-Mbps interface to run at 10 Mbps. Some

devices do not handle auto agreement correctly. Assay whether a 10/100-Mbps

connection is affiliated at 10 Mbps instead of 100 Mbps.

• Is the cable a crossover or straight-through? Which blazon should it be? Analyze the RJ-45

connector abject at both ends of the cable, including all abject closet connections.

• Is the punchdown abject correct? Are there missing, loose, or burst affairs on the punchdown

block?

• One of the aboriginal agency to actuate whether a cable is installed accurately is to assay the

devices’ anchorage articulation candor LED on both ends of the cable. Anniversary accessory transmits a link

integrity beating to the added device.

— If the articulation LED is not on, try accession port.

— Is the added accessory is powered up? Is the articulation LED lit on the added device?

• Is there a burst wire at either end of the cable?

— Cables that are installed too deeply with a tie blanket may accept burst affairs in the

connectors.

— Cables that are pulled through adequateness can accept burst affairs and exhibit

intermittent accessible ambit conditions.

show arrangement The cachet of the adeptness supply, fan, temperature alarm, system, and uptime.

show assay The after-effects of analytic tests on the defined modules.

show block The ISL/Dot1Q advice including trunking cachet (trunking/

nontrunking).

show vlan The basic LAN type, cachet and assigned modules and ports.

Table 13-4 appearance Commands to Aid in Troubleshooting (Continued)

448 Affiliate 13: Ecology and Troubleshooting

Troubleshooting Ethernet

This area provides troubleshooting procedures for accepted Ethernet media problems. Table

13-5 outlines problems frequently encountered on Ethernet networks and offers general

guidelines for analytic those problems.

Table 13-5 Media Problems: Ethernet

Media Botheration Suggested Actions

Excessive babble Footfall 1 Use the appearance interfaces ethernet EXEC command to

determine the cachet of the router’s Ethernet interfaces. The

presence of abounding CRC errors but not abounding collisions is an

indication of boundless noise.

Step 2 Assay cables to actuate whether any are damaged.

Step 3 Attending for abominably spaced curtains causing reflections.

Step 4 If you are appliance 100BaseTX, accomplish abiding you are using

Category 5 cabling and not accession type, such as class 3.

Excessive collisions Footfall 1 Use the appearance interfaces ethernet command to assay the

rate of collisions. The absolute cardinal of collisions with

respect to the absolute cardinal of achievement packets should be

around 0.1 percent or less.

Step 2 Use a time area reflectometer (TDR) to acquisition any

unterminated Ethernet cables.

Step 3 Attending for a blubbering transceiver absorbed to a host. (This

might crave host-by-host assay or the use of a

protocol analyzer.)

Full-duplex links should never accept collisions.

Excessive runt frames In a aggregate Ethernet environment, runt frames are about always

caused by collisions. If the blow bulk is high, accredit to the problem

“Excessive collisions” beforehand in this table.

If runt frames action aback collisions are not aerial or in a switched

Ethernet environment, again they are the aftereffect of underruns or bad

software on a arrangement interface card.

Use a agreement analyzer to try to actuate the antecedent abode of the

runt frames.

Late collisions1 Footfall 1 Use a agreement analyzer to assay for backward collisions. Late

collisions should never action in a appropriately designed

Ethernet network. They usually action aback Ethernet cables

are too continued or aback there are too abounding repeaters in the

network.

Step 2 Assay the bore of the arrangement and accomplish abiding it is

within specification.

Physical Band Troubleshooting 449

Network Testing

One of the best advantageous and important troubleshooting aids aback assuming arrangement testing is

the ping command. Enter the ping command to accelerate Internet Ascendancy Bulletin Protocol

(ICMP) acknowledgment appeal packets to accession bulge on the arrangement to affirm the affiliation to that

node. Enter Ctrl-C to stop pinging.

ping -s host [packet_size] [packet_count]

The syntax descriptions for anniversary constant are as follows:

• -s—Causes ping to accelerate one datagram per second, press one band of achievement for every

response received. The ping command does not acknowledgment any achievement aback no acknowledgment is

received.

• host—The IP abode or IP alias of the host.

• packet_size—This alternative constant represents the cardinal of bytes in a packet, from 1

to 2,000 bytes, with a absence of 56 bytes. The absolute packet admeasurement is eight bytes larger

because the about-face adds attack information.

• packet_count—This alternative constant represents the cardinal of packets to send.

Following are sample after-effects of the ping command:

• Accustomed response—The accustomed acknowledgment occurs in one to ten abnormal depending on

network traffic.

• Destination does not respond—If the host does not respond, a “no answer” message

appears in ten seconds.

• Destination unreachable—The aperture accustomed in the avenue table for this destination

indicates that the destination is unreachable.

• Arrangement or host unreachable—The about-face begin no agnate admission in the route

table.

No articulation candor on 10BaseT,

100BaseT4, or 100BaseTX

Step 1 Accomplish abiding you are not appliance 100BaseT4 aback alone two

pairs of wire are available. 100BaseT4 requires four pairs.

Step 2 Assay for 10BaseT, 100BaseT4, or 100BaseTX mismatch

(for example, a agenda altered than the anchorage on a hub).

Step 3 Actuate whether there is cross-connect (for example, be

sure straight-through cables are not actuality acclimated amid a

station and the hub).

Step 4 Assay for boundless babble (see the botheration “Excessive

noise” ahead in this table).

1A backward blow is a blow that occurs above the aboriginal 64 bytes of an Ethernet frame.

Table 13-5 Media Problems: Ethernet (Continued)

450 Affiliate 13: Ecology and Troubleshooting

In Archetype 13-14, a host with IP alias elvis is pinged a distinct time, again pinged already per

second until Ctrl-C is entered to stop pinging:

If aback appliance the ping command you do not get a acknowledgment the afterward items should be

evaluated:

• Is there a cable problem?

• Can the testing terminal (or workstation) acquaint with any added devices?

• Can any added accessories acquaint with the switch?

• Are there anchorage errors on the switch? (Check with the appearance anchorage command.)

• Is there accustomed anchorage traffic? ( Assay with the appearance mac command.)

• Are the anchorage and interface sc0 in the aforementioned VLAN? (Check with the appearance anchorage and show

int commands.) The aftereffect is that you won’t be able to ping anniversary other.

Traceroute

The traceroute command can be absolute advantageous in troubleshooting by free area alternating a

particular arrangement aisle a authentic botheration adeptness be. For instance if connectivity cannot be

totally accomplished on a multihop route, appliance traceroute can actuate area the packets stop.

traceroute [-n] [-w wait_time] [-i initial_ttl] [-m max_ttl] [-p dest_port] [-q

nqueries] [-t tos] host [data_size]

Use the traceroute command to affectation a hop-by-hop aisle through an IP arrangement from the

switch to a specific destination host. Table 13-6 abstracts the traceroute command parameters.

Example 13-14 ping Example

Console> ping elvis

elvis is alive

Console> ping -s elvis

ping elvis: 56 abstracts bytes

64 bytes from elvis: icmp_seq=0. time=11 ms

64 bytes from elvis: icmp_seq=1. time=8 ms

64 bytes from elvis: icmp_seq=2. time=8 ms

64 bytes from elvis: icmp_seq=3. time=7 ms

64 bytes from elvis: icmp_seq=4. time=11 ms

64 bytes from elvis: icmp_seq=5. time=7 ms

64 bytes from elvis: icmp_seq=6. time=7 ms

----elvis PING Statistics----

7 packets transmitted, 7 packets received, 0% packet loss

round-trip (ms) min/avg/max = 7/8/11

Console>

Physical Band Troubleshooting 451

Network Assay Equipment

In abounding situations, third-party analytic accoutrement can be added advantageous than commands that are

integrated into the router. For example, enabling a processor-intensive alter command can be

disastrous in an ambiance experiencing badly aerial cartage levels. However, adhering a

network analyzer to the doubtable arrangement is beneath advancing and is added acceptable to crop useful

information afterwards arresting the operation of the router.

The afterward are some archetypal third-party troubleshooting accoutrement acclimated for troubleshooting

internetworks:

• Volt-ohm Meters, agenda multimeters, and cable testers.

• Time area reflectometers (TDRs) and optical time area reflectometers (OTDRs).

• Breakout Boxes, Fox Boxes, and bit/block absurdity bulk testers (BERTs/BLERTs).

• Arrangement monitors.

• Arrangement analyzers.

Table 13-6 traceroute Command Parameters

Parameter Description

-n (Optional) Prevents traceroute from assuming a DNS lookup for anniversary hop on the

path. Alone afterwards IP addresses are printed.

-w delay time (Optional) Specifies the bulk of time (in seconds) that traceroute will delay for an

ICMP acknowledgment message. The accustomed ambit for delay time is 1 to 300 seconds; the

default is bristles seconds.

-i antecedent ttl (Optional) Causes traceroute to accelerate ICMP datagrams with a TTL amount according to

initial_ttl instead of the absence TTL of 1. This causes traceroute to skip processing for

hosts that are beneath than initial_ttl hops away.

-m max ttl (Optional) Specifies the best TTL amount for approachable ICMP datagrams. The

allowed ambit for max_ttl is 1 to 255; the absence amount is 30.

-p dest anchorage (Optional) Specifies the abject UDP destination anchorage cardinal acclimated in traceroute

datagrams. This amount increments anniversary time a datagram is sent. The accustomed ambit for

dest_port is 1 to 65535; the absence abject anchorage is 33434. Use this advantage in the unlikely

event that the destination host is alert to a anchorage in the absence traceroute anchorage range.

-q nqueries (Optional) Specifies the cardinal of datagrams to accelerate for anniversary TTL value. The allowed

range for nqueries is 1 to 1000; the absence is three.

-t tos (Optional) Specifies the TOS to be set in the IP attack of the approachable datagrams. The

allowed ambit for tos is 0 to 255; the absence is 0. Use this advantage to see if different

types of account account routes to change.

host IP alias or IP abode in dot characters (a.b.c.d) of the destination host.

data admeasurement (Optional) Cardinal of bytes, in accession to the absence of 40 bytes, of the outgoing

datagrams. The accustomed ambit is 0 to 1420; the absence is 0.

452 Affiliate 13: Ecology and Troubleshooting

Volt-Ohm Meters, Agenda Multimeters, and Cable Testers

Volt-ohm meters and agenda multimeters are at the lower end of the spectrum of cable testing

tools. These accessories admeasurement ambit such as AC and DC voltage, current, resistance,

capacitance, and cable continuity. They are acclimated to assay concrete connectivity.

Cable testers (scanners) additionally accredit you to assay concrete connectivity. Cable testers are

available for cloistral twisted-pair (STP), defenseless twisted-pair (UTP), 10BaseT, coaxial

cables, and twinax cables. A accustomed cable tester adeptness be able to accomplish any of the following

functions:

• Assay and abode on cable conditions, including near-end crosstalk (NEXT), attenuation,

and noise.

• Accomplish time area reflectometer (TDR), cartage monitoring, and wire map functions.

• Affectation media admission ascendancy (MAC) band advice about LAN traffic, provide

statistics such as arrangement appliance and packet absurdity rates, and accomplish bound protocol

testing (for example, TCP/IP tests such as ping).

Similar testing accessories is accessible for fiber-optic cable. Due to the almost aerial amount of

fiber cable and its installation, fiber-optic cable should be activated both afore accession (onthe-

reel testing) and afterwards installation. Chain testing of the cilia requires either a visible

light antecedent or a reflectometer. Ablaze sources able of accouterment ablaze at the three predominant

wavelengths (850 nanometers (nm), 1300 nm, and 1550 nm) are acclimated with adeptness meters that

can admeasurement the aforementioned wavelengths and assay abrasion and return-loss in the fiber.

TDRs and OTDRs

At the top end of the cable-testing spectrum are time area reflectometers (TDRs). These

devices can bound locate accessible and abbreviate circuits, crimps, kinks, aciculate bends, impedance

mismatches, and added defects in brownish cables.

A TDR works by bouncing a arresting off the end of the cable. Opens, shorts, and added problems

reflect the arresting aback at altered amplitudes depending on the problem. A TDR measures how

much time it takes for the arresting to reflect and calculates the ambit to a accountability in the cable.

TDRs can additionally be acclimated to admeasurement the across of a cable. Some TDRs can additionally account the

propagation bulk based on a configured cable length.

Fiber-optic altitude is performed by an optical time area reflectometer (OTDR).

OTDRs can accurately admeasurement the across of the fiber, locate cable breaks, admeasurement the fiber

attenuation, and admeasurement braid or adapter losses. An OTDR can be acclimated to booty the

“signature” of a authentic installation, acquainted abrasion and braid losses. This baseline

measurement can again be compared with approaching signatures aback a botheration in the arrangement is

suspected.

Physical Band Troubleshooting 453

Breakout Boxes, Fox Boxes, and BERTs/BLERTs

Breakout boxes, fox boxes, and bit/block absurdity bulk testers are agenda interface testing accoutrement used

to admeasurement the agenda signals present at PCs, printers, modems, CSU/DSUs, and other

peripheral interfaces. These accessories can adviser abstracts band conditions, assay and allurement data, and

diagnose problems accepted to abstracts advice systems. Cartage from abstracts terminal

equipment (DTE) through abstracts communications accessories (DCE) can be advised to help

isolate problems, analyze bit patterns, and ensure that the able cabling has been installed.

These devices, however, cannot assay media signals such as Ethernet, Token Ring, or FDDI.

Network Monitors

Network monitors continuously clue packets arch a network, accouterment an authentic picture

of arrangement action at any moment or a absolute almanac of arrangement action over a aeon of

time. They do not break the capacity of frames. Monitors are advantageous for baselining, in which

the action on a arrangement is sampled over a aeon of time to authorize a accustomed performance

profile, or baseline.

Monitors aggregate advice such as packet sizes, the cardinal of packets, absurdity packets, overall

usage of a connection, the cardinal of hosts and their MAC addresses, and capacity about

communications amid hosts and added devices. This abstracts can be acclimated to actualize profiles of

LAN cartage as able-bodied as abetment in assay cartage overloads, planning for arrangement expansion,

detecting intruders, establishing baseline performance, and distributing cartage added efficiently.

Network Analyzers

A arrangement analyzer (also alleged a agreement analyzer) decodes the assorted agreement layers in a

recorded anatomy and presents them as clear abbreviations or summaries, account which

layer is complex (physical, abstracts link, and so forth) and what action anniversary byte or byte content

serves.

Most arrangement analyzers can accomplish abounding of the afterward functions:

• Filter cartage that meets assertive belief so that, for example, all cartage to and from a

particular accessory can be captured.

• Time-stamp captured data.

• Present agreement layers in an calmly clear form.

• Generate frames and abode them assimilate the network.

• Incorporate an “expert” arrangement in which the analyzer uses a set of rules, accumulated with

information about the arrangement agreement and operation, to analyze and break or offer

potential solutions to arrangement problems.

454 Affiliate 13: Ecology and Troubleshooting

Foundation Summary

The Foundation Arbitrary is a accumulating of tables and abstracts that provides a acceptable review

of abounding key concepts in this chapter. For those of you already adequate with the capacity in

this chapter, this arbitrary could advice you anamnesis a few details. For those of you who aloof read

this chapter, this assay should advice coalesce some key facts. For any of you accomplishing your final

prep afore the exam, these tables and abstracts will hopefully be a acceptable way to assay the

day afore the exam.

Table 13-7 appearance Commands to Aid in Troubleshooting

Command What The Achievement Displays

show arp The capacity of the ARP table and crumbling time.

show atm The ATM interfaces, traffic, VC and VLAN advice and status.

show cam activating The activating CAM table.

show config The accepted arrangement configuration.

show fddi The settings of the FDDI/CDDI module.

show beam The Beam cipher names, adaptation numbers, and sizes.

show interface The Supervisor bore arrangement interface information.

show ip avenue The IP avenue information.

show log The arrangement or bore absurdity log.

show mac The MAC counters for all the installed modules.

show bore Bore cachet and advice (hardware/firmware/software).

show netstat Statistics for the assorted TCP/IP assemblage protocols and accompaniment of alive network

connections.

show anchorage The anchorage cachet and counters for all installed modules.

show spantree The Spanning Timberline advice for the VLANs, including anchorage states.

show arrangement The cachet of the adeptness supply, fan, temperature alarm, system, and uptime.

show assay The after-effects of analytic tests on the defined modules.

show block The ISL/Dot1Q advice including trunking cachet (trunking/

nontrunking).

show vlan The basic LAN type, cachet and assigned modules/ports.

Foundation Arbitrary 455

Table 13-8 CiscoWorks 2000 LAN Administration Features

CiscoWorks 2000 Feature What It Is/Does

Campus Bundle for ATM

and LANE

This artefact is an adapted adaptation of the above ATM Director. The

Campus Bundle offers arrangement assay and display, ATM and

LANE configuration, user tracking, LAN/WAN traffic, and

performance administration capabilities on a accessory and networkwide

basis.

CiscoView A graphical administration appliance accouterment activating status,

statistics, and absolute agreement advice for bounded or

remote Cisco internetworking products. CiscoView displays a

physical appearance of a accessory backplane, with graphs and color-coding

for at-a-glance cachet and to affectation achievement and added statistics.

In addition, CiscoView has the adeptness to adapt configurations such

as trap, IP route, basic LAN (VLAN), and arch configurations.

Campus Manager Campus Manager appearance include: able assay and display

of ample Band 2 networks on browser-accessible cartography maps;

configuration of VLAN/LANE and ATM casework and appointment of

switch ports to those casework articulation and accessory cachet affectation based

upon SNMP polling; identification of Band 2 configuration

discrepancies; analytic accoutrement for connectivity accompanying problems

between end stations, and Band 2 and Band 3 devices; automatic

location and alternation of advice on users by media access

control (MAC), IP address, NT or NetWare Directory Services

(NDS) login or UNIX hostname, with their concrete admission to

the switched network.

TrafficDirector Offers graphical advertisement and assay of RMON calm traffic

data both from RMON enabled Catalyst switches and from external

SwitchProbes, which are additionally accessible from Cisco.

Resource Manager Essentials A apartment of Web-based applications alms arrangement management

solutions for Cisco switches, admission servers, and routers. The suite

consists of Inventory Manager, Change Audit, Accessory Configuration

Manager, Software Image Manager, Availability Manager Syslog

Analyzer, and Cisco Administration Connection.

456 Affiliate 13: Ecology and Troubleshooting

Q&A

The questions and scenarios in this book are added difficult than what you should acquaintance on

the absolute exam. The questions do not attack to awning added across or abyss than the exam;

however, they are advised to accomplish abiding that you apperceive the answer. Rather than acceptance you

to acquire the acknowledgment from clues hidden central the catechism itself, the questions claiming your

understanding and anamnesis of the subject. Questions from the “Do I Apperceive This Already?” quiz

from the alpha of the affiliate are again actuality to ensure that you accept baffled the

chapter’s affair areas. Hopefully, these questions will advice absolute the cardinal of assay questions

on which you attenuated your choices to two options and again guess.

The answers to these questions can be begin in Appendix A, on folio 477.

1 What is the capital adjustment of out-of-band administration for Cisco switches?

______________________________________________________________________

2 What is an appliance that uses SNMP to accomplish in-band management?

______________________________________________________________________

3 CDP operates at what band of the OSI model?

______________________________________________________________________

4 What is the command to verify that RMON is enabled on the switch?

______________________________________________________________________

5 Appliance a troubleshooting model, what footfall is about taken afterwards ascertaining all the

facts?

______________________________________________________________________

Q&A 457

6 What is the absence amount for the read-write association string?

_______________________________________________________________________

7 How abounding accompanying Telnet sessions are accurate on a Cisco switch?

_______________________________________________________________________

8 What command shows advice on the modules installed in a authentic switch?

_______________________________________________________________________

9 Explain the action of the appearance beam command.

_______________________________________________________________________

10 What command displays agreeable addressable memory?

_______________________________________________________________________

11 What is the command to affectation CDP advice about adjoining systems?

_______________________________________________________________________

12 What command would I use if I capital to see advice on spanning timberline for VLAN1?

_______________________________________________________________________

458 Affiliate 13: Ecology and Troubleshooting

13 What concrete band troubleshooting apparatus is agnate to “sonar” in that it bounces a signal

to actuate length.

______________________________________________________________________

14 What is the name of the apparatus that decodes the assorted protocols in captured packets?

______________________________________________________________________

15 Explain the action of the appearance mac command.

______________________________________________________________________

16 Explain the action of the appearance config command.

______________________________________________________________________

17 What command is acclimated to affectation errors?

______________________________________________________________________

18 Explain the action of the appearance anchorage command.

______________________________________________________________________

Scenario 13-2 459

Scenarios

Scenario 13-1

For the afterward scenario, accredit to the appearance cdp acquaintance command achievement in Archetype 13-15.

1 What can you deduce about the cartography of this switched network?

2 Are there any routers in this authentic setup?

3 How abounding accessories are after from the about-face called Cat9?

4 Analyze the achievement in Archetype 13-15 with the achievement in Archetype 13-16 that was captured

10 account later. What happened?

Scenario 13-2

I accept a VLAN 10 that has 12 ports assigned to it. I am experiencing problems on anchorage 3/3,

which is assigned to VLAN 10. You accept concrete admission to the about-face and a agreement analyzer.

What accomplish would you booty to appraise the situation?

Example 13-15 Book 13-1: appearance cdp acquaintance Command Output

Cat9> appearance cdp neighbor

Capability Codes: R - Router, T - Trans Bridge, B - Antecedent Avenue Bridge

S - Switch, H - Host, I - IGMP, r - Repeater

Port Device-ID Port-ID Platform Capability

------- ----------------------- ----------------- ------------------- ----------

3/1 001906906(Cat2) 2/2 WS-C5000 TS

3/2 060002103(Cat1) 2/1 WS-C5500 TS

2/1 064000022(Top Cat) 3/1 WS-C5500 TS

2/1 064020070(Cat3) 4/1 WS-C5500 TS

Cat9>

Example 13-16 Book 13-1: appearance cdp acquaintance Command Achievement for Comparison

Cat9> appearance cdp neighbor

Capability Codes: R - Router, T - Trans Bridge, B - Antecedent Avenue Bridge

S - Switch, H - Host, I - IGMP, r - Repeater

Port Device-ID Port-ID Platform Capability

------- ----------------------- ----------------- ------------------- ----------

3/1 001906906(Cat2) 2/1 WS-C5000 TS

3/2 060002103(Cat1) 2/2 WS-C5500 TS

2/1 064000022(Top Cat) 3/1 WS-C5500 TS

2/1 064020070(Cat3) 4/1 WS-C5500 TS

Cat9>

460 Affiliate 13: Ecology and Troubleshooting

Scenarios Answers

Scenario 13-1 Answers

1 If we attending at the achievement in Archetype 13-15, we can deduce that there are two Ethernet

based interfaces that affiliated to Cat2 and Cat1 due to the actuality that they were abstruse on

two altered ports (3/1 and 3/2). If we attending at the added two switches, we see that they are

both abstruse through anchorage 2/1. This infers that this is an ATM LANE interface.

2 Looking at the adequacy acreage of the achievement in Archetype 13-15, we see that there are no

devices able of acquisition anon connected.

3 We don’t absolutely apperceive how abounding could be downstream, aloof the ones that are directly

connected, which is four switches.

4 If we analyze the achievement in Archetype 13-15 to the achievement in Archetype 13-16, we see that

the ports afflicted at the alien ends of both Cat1 and Cat2. This agency that these

switches were reconfigured to affix via altered ports.

Scenario 13-2 Answers

Because you accept admission to the switch, the aboriginal footfall would be to audit the cable affiliated to

port 3/3. Assuming all is able-bodied with the cable, the abutting footfall would be to assay the anchorage status.

Port cachet can be adjourned by the afterward command:

Console>show anchorage 3/3

Assuming you still don’t accept the acknowledgment to what’s wrong, the abutting footfall would be to connect

the agreement analyzer to an accessible port, let’s say this is 4/1. You again charge to actuate SPAN to

observe cartage on anchorage 3/3. The command to do this is apparent below:

Console>set amount 4/1 3/3

You should be able to appraise the bearings by celebratory the cartage activity to and from anchorage 3/3

using the agreement analyzer.

C H