2.3. Extension Headers

The IPv4 header can be extended from a minimum of 20 bytes to 60 bytes in order to specify options such as Security Options, Source Routing, or Timestamping. This capacity has rarely been used because it causes a performance hit. For example, IPv4 hardware forwarding implementations have to pass the packet containing options to the main processor (software handling).

The simpler a packet header, the faster the processing. IPv6 has a new way to deal with options that has substantially improved processing. It handles options in additional headers called Extension headers.