With IPv4, it may be necessary to use options to provide source routing information, timestamps, and others. Several of the IP options have been deprecated and are no longer used. For a more compete discussion, refer to RFC 6814. A current list can be found at https://www.iana.org/assignments/ip-parameters/ip-parameters.xhtml#ip-parameters-1, which was updated on May 3, 2018.

When used, the options field must be a multiple of 32-bit, or 4 bytes. Padding may be required so that the header is a multiple of 32-bit.

Now that we have reviewed IPv4, let's take a closer look at IPv6.