IPv6 extension headers describe processing options.
Each extension header contains a separate category of options and is identified by a number, similar to protocol identification numbers.
An IPv6 packet can include extension headers, but they are not mandatory.
The following figure illustrates the IPv6 header with extension headers.
IPv6 examines the destination address in the main header of each packet it receives.
the packet destination - if the router is the packet destination, IPv6 examines the header extensions that contain options for destination processing.
an intermediate node in the packet data path - if the router is an intermediate node, IPv6 examines the header extensions that contain forwarding options.
By examining only the extension headers that apply to the operations it performs, IPv6 reduces the amount of time and resources required to process a packet.
Extension header name | Description |
|---|---|
hop-by-hop | Contains optional information, and sub-options for Router Alert and Jumbo Payload, that all intermediate IPv6 routers examine between the source and the destination. |
destinations-options | Contains optional information for the destination node. This option can appear twice, once for way points and once for final destination. |
source-routing | Contains a list of one or more intermediate nodes that define a path for the packet to follow through the network to the destination. The packet source creates this list. The source-routing function is similar to the IPv6 source routing options. |
fragmentation | Uses an IPv6 source to send packets larger than the size specified for the path maximum transmission unit (MTU). |
authentication | provides security for IPv6 datagrams |
encapsulated security payload (ESP) | provides security for IPv6 datagrams |
The authentication extension header and the encapsulated security payload extension header can be used together to provide security services for IPv6 datagrams. | |
Hop-by-hop
Destination option 1
Routing
Fragmentation
Authentication/ESP
Destination Option 2
The presence of particular extension headers within a packet can cause slower packet processing if the IPv6 implementation handles only certain headers and diverts others to a slow path. For example, many IPv6 implementations usually process Hop-by-Hop extension headers on the control plane.