Source Address (128 bits)The Source Address field contains the IPv6 address for the packet originator.Destination Address (128 bits)The Destination Address field contains the intended recipient’s IPv6 address. This can be either the ultimate destination or the address ofthe next hop router.Extension Header FieldsExtension headers are used only when necessary. Due to the streamlined nature of the IPv6 header, adding extension headers do notseverely impact performance. Each Extension headers’s lengths vary, but they are always a multiple of 8 bytes.Each extension header is identified by the Next Header field in the IPv6 header that precedes it. Extension headers are viewed only by thedestination router identified in the Destination Address field. If the Destination Address is a multicast address, the Extension headers areexamined by all the routers in that multicast group.However, if the Destination Address is a Hop-by-Hop options header, the Extension header is examined by every forwarding router alongthe packet’s route. The Hop-by-Hop options header must immediately follow the IPv6 header, and is noted by the value 0 (zero) in theNext Header field.Extension headers are processed in the order in which they appear in the packet header.Hop-by-Hop Options HeaderThe Hop-by-Hop options header contains information that is examined by every router along the packet’s path. It follows the IPv6 headerand is designated by the Next Header value 0 (zero).When a Hop-by-Hop Options header is not included, the router knows that it does not have to process any router specific information andimmediately processes the packet to its final destination.When a Hop-by-Hop Options header is present, the router only needs this extension header and does not need to take the time to viewfurther into the packet.The Hop-by-Hop Options header contains:• Next Header (1 byte)This field identifies the type of header following the Hop-by-Hop Options header and uses the same values.• Header Extension Length (1 byte)This field identifies the length of the Hop-by-Hop Options header in 8-byte units, but does not include the first 8 bytes. Consequently, if theheader is less than 8 bytes, the value is 0 (zero).• Options (size varies)This field can contain one or more options. The first byte if the field identifies the Option type, and directs the router how to handle theoption.00 Skip and continue processing.01 Discard the packet.454 IPv6 Routing
