Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 144
IPv4 Options — A Review

With the IP header becoming fixed, all of the options fields in the header were not eliminated completely, they merely changed forms. Basically, IPv4 options are now IP header extensions. The following are the IPv4 options:

Security. Used to carry security, compartmentation, user group (TCC), and handling restriction codes compatible with DOD requirements.

Loose source routing. Variable in length and used to route the internet datagram based on information supplied by the source. Not all the routing hops will be in this field. This option allows some flexibility in providing a path.

Strict source routing. Variable in length and used to route the internet datagram based on information supplied by the source. The routing information provided in this field must be explicitly followed.

Record route. Variable in length and used to trace the route an internet datagram takes.

Stream ID. Used to carry the stream identifier.

Internet timestamp. The timestamp is a right-justified, 32-bit field that indicates a time in milliseconds since midnight UT (Universal Time). There are placeholders for multiple timestamps and a flags field to indicate timestamps only. A timestamp is preceded with the internet address of the registering entity, the internet address fields are prespecified, or an IP module only registers its timestamp if it matches its own address with the next specified internet address. This can be used for measurements of the transport layer protocols and other utilities.