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Internetwork Troubleshooting

1© 2000, Cisco Systems, Inc. © 2000, Cisco Systems, Inc.

Catalyst 6000 UpdateAsia PAC - March 2000

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Course Agenda

• Resources for Troubleshooting

• Using a Systematic Troubleshooting Method

• Data-Link Troubleshooting Targets

• Applying Cisco Troubleshooting Tools

• Diagnosing and Correcting TCP/IP Problems

• Frequency Faced Problems

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Resources for Troubleshooting

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Resources for Troubleshooting

• Network Media Test Equipment

• Network Monitors

• Protocol Analyzers

• Network Management Systems

• Telephone

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Network Media Test Equipment

• Cable tester

Near-end Crosstalk (NEXT)

Time Domain Reflectometer (TDR)

Wire Map

• Volt-ohm meters

• Fiber-optic Cable Testers

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Network Management Systems

• Fault Management

• Accounting Management

• Configuration and Name Management

• Performance Management

• Security Management

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Course Agenda

• Catalyst 6000 Switch Overview

• System Architecture

• Configure the Catalyst 6000 Switch

• Configure Virtual LANs

• Configure ATM LANE Modules

• Configure MSFC

• Troubleshooting the Catalyst 6000 Switch

• Configuration Example

Using a Systematic Troubleshooting Method

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Using a Systematic Troubleshooting Method

• Restoring an internetwork that has failed puts incredible pressure no network engineers and network administrator

• Use special known expertise and short cuts

requires technical depth and a detailed breadth of knowledge

• Unsystematic approach result in wasting time

• Documenting helps to capture, preserve, and communicate the experience

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Problem Solving Model

Define ProblemDefine Problem

Gather FactsGather Facts

Create Action PlanCreate Action Plan

Consider PossibilitiesConsider Possibilities

Iterate ProcessIterate Process

Implement Action PlanImplement Action Plan

Observe ResultsObserve Results

Problem ResolvedProblem Resolved

Document FactsDocument Facts

DoProblem

SymptomsStop

?

Start

no

yes

Finished

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A Sample Network Problem

TokenRing

WAN

Network T

Network R Network S

Host 1

Host 2

Host 3

Host B

Host A

Host 4

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Problem Resolution

Define ProblemDefine Problem

Gather FactsGather Facts

Create Action PlanCreate Action Plan

Consider PossibilitiesConsider Possibilities

Iterate ProcessIterate Process

Implement Action PlanImplement Action Plan

Observe ResultsObserve Results

Problem ResolvedProblem Resolved

Document FactsDocument Facts

DoProblem

SymptomsStop

?

Start

no

yes

Finished

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ATU_R 的基本設定

• 簡單的基本指令set

show

• set int vip0 ip 10.0.0.1

• set int vip0 mask 255.0.0.0

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NAT安裝與設定

• 簡介NAT (Network Address Translation) 可以讓你區域網路中的所

有機器經由一台通往 Internet 的 server 連線出去，而且只需要註冊該 server一個 IP 就夠了。

• private IP，依照 RFC 1918 規範, 預留 private network10.0.0.0 - 10.255.255.255/255.0.0.0172.16.0.0 - 172.31.255.255/255.240.0.0192.168.0.0 - 192.168.255.255/255.255.255.0

優點:網路設計有彈性, 節省 ip

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NAT安裝與設定

運作原理 :

當 packet 要送往網路上時 , 所走的途徑是 1-2-3-4-5 當 packet 從網路上傳入時 , 所走的途徑是 6-2-3-4-7

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安裝與設定

• OS :FreeBSD,Linux,Solaris…

• 在 Kernel File 中加入以下兩個 option, 並重新 make kernel

options IPFIREWALL

options IPDIVERT

• 確定 NAT主機上兩張網路卡都有被正常地啟動, 可以透過更改 /etc/rc.conf 來啟動所有的網路卡或是在 /etc/rc.local 手動用 ifconfig ed1 the_private_ip netmask 255.255.255.0 up

( 我們假設 ed0 是擁有 public IP 的 interface,而 ed1 是對內的 interface)

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安裝與設定

• 確定有 NAT主機會 forward packet, 方法有兩種 將 /etc/rc.conf 的 gateway_enable=YES, 或是在 /etc/rc.local 加入或手動執行下面這一行 sysctl -w net.inet.ip.forwarding=1

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安裝與設定

• 啟動 NAT daemon 在 /etc/services 加入 (3.0 Release 以後已內建 , 可省略 ) natd 8668/divert # NAT divert socket

加入 /etc/rc.local 或手動執行 natd natd -interface ed0

( 此處 ed0 為你擁有 public IP 的 interface)

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安裝與設定

• 最後是設定有關 IPFW 的部份 , 首先將 /etc/rc.conf 中的 firewall_enable=YES, 由於我們只是要利用 IPFW 來將 packet 轉往 divert socket, 因此我們不需要複雜的 firewall 設定 , 故將原本的 rc.firewall 改名 成 rc.firewall.orig, rc.firewall 只需要下列幾行 /sbin/ipfw -f flush

/sbin/ipfw add divert natd all from any to any via ed0

/sbin/ipfw add pass all from any to any