Headers containing options may provide some additional information related to the datagram or its processing. They are separated into two groups: options dedicated to every node forwarding the datagram (hop-by-hop options), and options intended for the destination host only (destination options). Table 2-2, “Hop-by-hop options” and Table 2-3, “Destination options” contain the list of defined options.

Hop-by-hop options (if present) are placed at the start of extension headers chain, because they are important for every node forwarding the datagram. The location of destination options is a bit more complicated. Actually there are two kinds of destination options: options dedicated to the final target (they are located on the end of extension headers chain) and options assigned to the next host specified by Routing header (located just before the Routing header).

Table 2-2 Hop-by-hop Options

Table 2-3 Destination Options

The meaning of the individual options is as follows:

Pad1, PadN

Padding. They do not carry any content, they just align the following content to the appropriate position.

Router alert

Advice to the router on content which may be important. For example RSVP sends control messages dedicated to all routers along the path, so they are equipped with a Router alert option announcing that an RSVP message is carried by the datagram.

Jumbo payload

Allows the transportation of datagrams which exceed the 64 KB maximum. The hop-by-hop option asks for special handling which is necessary to process these jumbograms.

Home Address

It is a part of the mobility support. It contains the home (stable) address of the travelling mobile node.