Technical data

Contents

Preface ............................................................ vii

1 Troubleshooting Techniques and Tools

1.1 Using Symptoms to Identify a Problem ........................... 1–1

1.2 Isolating Problems . . . ........................................ 1–1

1.2.1 Testing Connectivity Between Network Hosts ................... 1–3

1.2.1.1 Using ping on a Multihomed Host . . ....................... 1–5

1.2.2 Checking the Network Interface Parameters .................... 1–5

1.2.3 Displaying and Modifying the Internet-to-Ethernet Translation

Tables . . ................................................ 1–6

1.2.4 Examining Network Statistics ............................... 1–7

1.2.5 Monitoring Network Trafﬁc . ................................ 1–8

1.2.5.1 Using TCPTRACE ..................................... 1–9

1.2.5.2 Using TCPDUMP ...................................... 1–9

1.2.5.2.1 Building Expressions ................................ 1–9

1.2.5.2.2 Keywords for Filtering Traces from non-OpenVMS

Systems . . ........................................ 1–11

1.2.5.2.3 Primitive Keywords . ................................ 1–12

1.2.5.2.4 Primitive Expressions ............................... 1–12

1.2.5.2.5 Accessing Data Inside Packets . . ....................... 1–14

1.2.5.2.6 Combining Keywords ................................ 1–15

1.2.5.3 Analyzing Output ...................................... 1–16

1.2.5.3.1 Link Level Headers . ................................ 1–16

1.2.5.3.2 ARP Packets ...................................... 1–16

1.2.5.3.3 TCP Packets ...................................... 1–16

1.2.5.3.4 UDP Packets ...................................... 1–18

1.2.5.3.5 UDP Name Server Requests . . . ....................... 1–18

1.2.5.3.6 UDP Name Server Responses . . ....................... 1–18

1.2.5.3.7 Sun RPC Requests and Replies . ....................... 1–19

1.2.5.3.8 IP Fragmentation . . . ................................ 1–21

1.2.5.3.9 Timestamps ....................................... 1–21

1.2.5.4 Restrictions . . ........................................ 1–22

1.2.5.5 Reducing Discarded Packets ............................. 1–22

1.2.6 Monitoring Socket Activity . . ................................ 1–22

1.2.7 Checking Name Server Operation ............................ 1–23

1.2.8 Checking the Route to a Remote Host . . ....................... 1–25

1.2.9 Checking the Routes Known to a Gateway ..................... 1–26

1.2.10 Determine Whether Network Services Are Available .............. 1–27

1.2.10.1 Displaying the Service Database . . . ....................... 1–27

1.2.10.2 Displaying Service Attributes ............................ 1–28

1.2.10.3 Verifying Process Privileges .............................. 1–29

1.2.10.4 Verifying Account Privileges ............................. 1–29

1.2.10.5 Looking for OPCOM Messages ............................ 1–30

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