TAILIEUCHUNG - Internetworking with TCP/IP- P66

Internetworking with TCP/IP- P66: TCP/IP has accommodated change well. The basic technology has survived nearly two decades of exponential growth and the associated increases in traffic. The protocols have worked over new high-speed network technologies, and the design has handled applications that could not be imagined in the original design. Of course, the entire protocol suite has not remained static. New protocols have been deployed, and new techniques have been developed to adapt existing protocols to new network technologies | Sec. IPv6 Source Routing 609 IPv6 Options It may seem that IPv6 extension headers completely replace IPv4 options. However the designers propose two additional extension headers to accommodate miscellaneous information not included in other extension headers. The additional headers are a Hop By Hop Extension Header and an End To End Extension Header. As the names imply the two headers separate the set of options that should be examined at each hop from the set that are only interpreted at the destination. Although each of the two option headers has a unique type code both headers use the format illustrated in Figure . 0 8 16 31 NEXT HEADER HEADER LEN ONE OR MORE OPTIONS Figure The format of an IPv6 option extension header. Both the hop-by-hop and end-to-end option headers use the same format the NEXT HEADER field of the previous header distinguishes between the two types. As usual field NEXT HEADER gives the type of the header that follows. Because an option header does not have fixed size the field labeled HEADER LEN specifies the total length of the header. The area labeled ONE OR MORE OPTIONS represents a sequence of individual options. Figure illustrates how each individual option is encoded with a type length and valuet options are not aligned or padded. 0 8 16. TYPE LENGTH VALUE Figure Encoding of an individual option in an IPv6 option extension header. Each option consists of a one-octet type and a one-octet length followed by zero or more octets of data for the option. As the figure shows IPv6 options follow the same form as IPv4 options. Each option begins with a one-octet TYPE field followed by a one-octet LENGTH field. If the option requires additional data octets that comprise the VALUE follow the LENGTH. fin the literature an encoding of type length and value is sometimes called a TLV encoding. 610 The Future Of TCP IP IPv6 Chap. 33 The two high-order bits of each option TYPE field specify how a host or router should .

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