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Internet Core Protocols: The Definitive Guide
book

Internet Core Protocols: The Definitive Guide

by Eric Hall
February 2000
Intermediate to advanced
464 pages
15h 57m
English
O'Reilly Media, Inc.
Content preview from Internet Core Protocols: The Definitive Guide

Name

Source Port

Synopsis

Identifies the message’s original sender, as referenced by the 16-bit UDP port number in use by the application.

Size

Sixteen bits.

Notes

This field identifies the port number used by the application that created the data.

Note that RFC 768 states “Source Port is an optional field, when meaningful, it indicates the port of the sending process, and may be assumed to be the port to which a reply should be addressed in the absence of any other information. If not used, a value of zero is inserted.”

Although Source Port is optional, it should always be used.

Capture Sample

In the capture shown in Figure 6.4, the Source Port field is set to hexadecimal 04 2c, which equates to decimal 1068.

The Source Port field
Figure 6.4. The Source Port field
See Also

Destination Port

UDP Ports

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Publisher Resources

ISBN: 1565925726Errata Page