Technical data

Troubleshooting Techniques and Tools
1.2 Isolating Problems
1.2.5.1 Using TCPTRACE
The trace utility (TCPTRACE) is a tool you can use to trace packets going in and
out of the system. To run the trace utility, enter the DCL command TCPTRACE.
Use the qualifiers listed in the command reference section to customize tracing
for your particular problem. For example:
$ TCPTRACE HOST1 /FULL /PORT=REMOTE=21
$ TCPTRACE HOST2 /PORT=(LOCAL=23, REMOTE=1056) /FULL /PACKETS=30 /OUTPUT=TELNET_TRACE.TXT
The following sample is a TCPTRACE display:
TCPIP INTERnet trace RCV packet seq # = 1 at 23-OCT-1998 15:19:33.29
IP Version = 4, IHL = 5, TOS = 00, Total Length = 217 = ^x00D9
IP Identifier = ^x0065, Flags (0=0,DF=0,MF=0),
Fragment Offset = 0 = ^x0000, Calculated Offset = 0 = ^x0000
IP TTL = 32 = ^x20, Protocol = 17 = ^x11, Header Checksum = ^x8F6C
IP Source Address = 16.20.168.93
IP Destination Address = 16.20.255.255
UDP Source Port = 138, UDP Destination Port = 138
UDP Header and Datagram Length = 197 = ^x00C5, Checksum = ^x0E77
5DA81410 8F6C1120 00000065 D9000045 0000 E...awe.....l....]
| 0E77C500 8A008A00 | FFFF1410 0010 ..........w.
For more information about using TCPTRACE, see Appendix A.
1.2.5.2 Using TCPDUMP
The OpenVMS
tcpdump utility can trace natively on Ethernet or can format traces
taken on another host. It communicates with the TCP/IP kernel in copy-all mode
so it only can trace packets received or transmitted by the TCP/IP kernel.
The trace can be taken interactively and ended with Ctrl/C, or continue until a
packet count has been reached (specified using
-c count ). The tcpdump utility
displays a summary line indicating the number of packets traced and the number
of packets discarded by the kernel.
To use tcpdump , no special TCP/IP Services configuration is required. The process
using tcpdump must have OPER, PSWAPM, and CMKRNL privileges.
The format and options are described in Appendix A. This section describes:
• How to build expressions (Section 1.2.5.2.1)
• How to analyze output from tcpdump (Section 1.2.5.3)
• Restrictions on using OpenVMS tcpdump (Section 1.2.5.4)
• How to reduce discarded packets (Section 1.2.5.5)
1.2.5.2.1 Building Expressions The expression is used to select the packets
to dump. If no expression is given, all packets on the network are dumped.
Otherwise, only packets for which expression is TRUE are dumped.
The expression consists of one or more primitives. Primitives usually consist of an
identifier (name or number) preceded by one or more of the keywords described in
Table 1–3.
Troubleshooting Techniques and Tools 1–9