Dell Force10 S25N-S50N FTOS Configuration Guide FTOS 8.4.2.7 E-Series TeraScal - Page 485

IPv6 Headers The IPv6 header has a fixed length of 40 bytes. This provides 16 bytes each for Source and Destination information, and 8 bytes for general header information. The IPv6 header includes the following fields: • Version (4 bits) • Traffic Class (8 bits) • Flow Label (20 bits) • Payload Length (16 bits) • Next Header (8 bits) • Hop Limit (8 bits) • Source Address (128 bits) • Destination Address (128 bits) IPv6 provides for Extension Headers. Extension Headers are used only if necessary. There can be no extension headers, one extension header or more than one extension header in an IPv6 packet. Extension Headers are defined in the Next Header field of the preceding IPv6 header. IPv6 header fields The 40 bytes of the IPv6 header are ordered as show in Figure 22-1. Figure 22-1. IPv6 Header Fields 0 4 8 12 Version Traffic Class Payload Length 16 20 24 Flow Label Next Header 28 Hop Limit 32 64 Source Address 128 192 Destination Address 320 Version (4 bits) The Version field always contains the number 6, referring to the packet's IP version. IPv6 Addressing | 485