The IP datagram header is normally 20 bytes long. The IP protocol allows for up to 40 additional bytes of optional fields. Only 8 options are considered valid in IP version 4.

The following are IP options:

• COPY (Bit 0)—Specifies to routers if the option information should be included in fragment headers.
• CLASS (Bits 1-2)—Specifies 1 of 2 valid option classes: Network Control, Debugging
• OPTION (Bits 3-7)—Specifies one of eight valid IP options. Option zero indicates the end of the list.
• Option 0—End of Options: self-explanatory.
• Option 1—No Operation: self-explanatory.
• Option 2—Security: this option is specific to the U.S. government. May carry the following s-security clearance, c-compartment, h-handling codes, and tcc-user group.
• Option 3—Loose Source Route: this is a list of router addresses to be visited in transit, though other routers may be visited as well.
• Option 4—Timestamp: self-explanatory.
• Option 7—Record Route: applications may request the route a packet takes be recorded.
• Option 8—Stream ID: self-explanatory.
• Option 9—Strict Source Route: is a list of router addresses that must be followed by the packet.
• LENGTH (Bits 8-15)—Specifies the total number of bytes in the option, if used by the option.
• PARAMETER (Bytes 3-40)—The parameters passed by the specific option.