Information Technology Reference
In-Depth Information
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An option-type byte.
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An option-type byte, followed by an option-length byte, and then the actual option-data
bytes. The option-length byte counts all the bytes in the options field.
The option-type byte is the first byte and has three fields, as illustrated in Figure 23.13. The
copied flag indicates that this option is (or is not) copied into all fragments on fragmentation.
Option classes
00 - Control
01 - Reserved
10 - Debugging
11 - Reserved
Copied flag
0 - No copied
1 - Copied
Number
0 - End of Option List ( followed by 0 bytes)
1 - No operation (followed by 0 bytes)
2 - Security (followed by 11 bytes)
3 - Loose Source Routing (followed by variable bytes)
4 - Internet Timestamp (followed by variable bytes)
7 - Record Route (followed by variable bytes)
8 - Stream ID (followed by 4 bytes)
9 - Strict Source Routing (followed by variable bytes)
Figure 23.13
Options-type byte
End of option list (Type = 0)
This option indicates the end of the option list, but does not necessarily need to coincide with
the end of the IP header according to the internet header length. It is used at the end of all
options, but not the end of each option. It may be copied, introduced, or deleted on fragmen-
tation, or for any other reason.
No operation (type = 1)
This option may be used between options, and can be used to align the beginning of a subse-
quent option on a 32-bit boundary. It may be copied, introduced, or deleted on fragmenta-
tion, or for any other reason.
Security (type = 130)
This option allows hosts to send security, compartmentation, handling restrictions, and TCC
(closed user group) parameters. In this option, the Type field is a 2, and the Class field is also
a 2. Thus the option-type byte has a value of 130 (0100 0010), and has 11 bytes in total. Its
format is
+--------+--------+---...---+---...---+---...---+---...---+
|10000010|00001011|SSS SSS|CCC CCC |HHH HHH | TCC |
+--------+--------+---...---+---...---+---...---+---...---+
