1-1 Internetwork Troubleshooting 1 © 2000, Cisco Systems, Inc. Catalyst 6000 Update Asia PAC - March 2000

1-2 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

1-3 Resources for Troubleshooting 3

1-4 Resources for Troubleshooting Network Media Test Equipment Network Monitors Protocol Analyzers Network Management Systems Telephone

1-5 Network Media Test Equipment Cable tester Near-end Crosstalk (NEXT) Time Domain Reflectometer (TDR) Wire Map Volt-ohm meters Fiber-optic Cable Testers

1-6 Network Management Systems Fault Management Accounting Management Configuration and Name Management Performance Management Security Management

1-7 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 7

1-8 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

1-9 Problem Solving Model Define Problem Gather Facts Create Action Plan Consider Possibilities Iterate Process Implement Action Plan Observe Results Problem Resolved Document Facts Do Problem Symptoms Stop ? Start no yes Finished

1-10 A Sample Network Problem WAN Network T Network R Network S Host 1 Host 2 Host 3 Host B Host A Host 4

1-11 Problem Resolution Define Problem Gather Facts Create Action Plan Consider Possibilities Iterate Process Implement Action Plan Observe Results Problem Resolved Document Facts Do Problem Symptoms Stop ? Start no yes Finished

1-12 ATU_R 的基本設定 簡單的基本指令 set show set int vip0 ip set int vip0 mask

1-13 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 network / / / 優點 : 網路設計有彈性, 節省 ip

1-14 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 當 packet 從網路上傳入時, 所走的途徑是

1-15 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 up ( 我們假設 ed0 是擁有 public IP 的 interface, 而 ed1 是對內 的 interface)

1-16 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

1-17 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)

1-18 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