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  • Book Overview & Buying iOS and OS X Network Programming Cookbook
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iOS and OS X Network Programming Cookbook

iOS and OS X Network Programming Cookbook

By : Jon Hoffman
4.5 (6)
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iOS and OS X Network Programming Cookbook

iOS and OS X Network Programming Cookbook

4.5 (6)
By: Jon Hoffman

Overview of this book

Table of Contents (15 chapters)
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iOS and OS X Network Programming Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
1
Index

Decoding ICMP headers


In the Decoding IP headers recipe of this chapter, we created a decodeIp() function that decoded the IP headers of a packet. If the protocol type was ICMP in that function, we called a decodeICMP() function. We will create the decodeICMP() function in this recipe.

Even though our layer diagram shows the ICMP packet as a part of the Internet layer, from the libpcap point of view, it is a part of the third layer (Protocol layer) of our header stack; this is because the IP header encapsulates the ICMP header.

The ICMP header looks like this:

The components are explained as follows:

  • ICMP Type: This field identifies the ICMP message type. The Echo request message is type 8 and the Echo reply is type 0.

  • Code: This field is not used in the Echo request or reply so this is set to 0.

  • Checksum: This field contains the checksum for the ICMP header.

  • Identifier: This is the identification field that can be used to match the Echo request with an Echo reply.

  • Sequence Number: This field contains...

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iOS and OS X Network Programming Cookbook
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