cisco ccna bundle

cisco ccna bundle.Figure 23.4 shows the IPv4 header and its fields. Such a header contains 12 essential fields, and a variable-length optionala field. The IPv4 header is 20 bytes long when no options are included, and up to 40 bytes long when options are included. In the IPv6 header, six fields from the IPv4 header have been removed and are marked in gray in Figure 23.4. . Header length: In IPv6, it is no longer needed because the length of an IPv6 header is fixed. . Identifier: in IPv4, this feature has not been used for a long time, and IPv6 does not use it. . Flags: In IPv4, this feature has not been used for a long time, and IPv6 does not use it. . Segment Offset: In IPv6, segments are handled differently and it is no longer necessary to include this field in the IPv6 header (it is moved to thethe IPv6 Extended Header Information field) o . Header checksum: today's data link layer technology is so reliable that this field is no longer needed for IPv6. . Padding: in IPv6, this field is no longer needed.Chapter 23 IPv6 617Figure 23.5 shows the fields in the IPv6 header, and a description of the eight fields is given below. . Version: 4 bits long and contains the number 6 instead of 4. . Traffic Class: 8 bits long, similar to the ToS field in the IPv4 header. . Flow Label: 20 bits long, new for IPv6, no corresponding IPv4 field; used to identify individual flows and allow routing devices toenable routing devices to perform additional policy functions. . Payload length: 16 bits long, indicates the length of the payload. In IPv4, the total packet length field indicates the length of the entirepacket, while in IPv6, the payload length field does not contain the length of the IPv6 header. . Next header: 8 bits long, functions the same as the protocol field in the IPv4 header. . Hop limit: 8 bits long, same function as the TTL field in the IPv4 header. . Source IP address: 128 bits long (16 bytes), indicates the source IPv6 address. . Destination IP address: 128 bits (16 bytes) long, indicates the destination IPv6 address.40 bytesvariable lengthA----------------------------------------------32 bitmap 23.5 IPv6 Header These 8 bytes are followed by extension headers (if any), which replace the option fields in IPv4. The number of extension headers is not fixed, so the total length of the extension header information field (extension header list) is not fixed. As can be seen in Figure 23.4 and Figure 23.5, the IPv6 header is simpler-containing fewer fields.