Dell Force10 S4820T S4820T Configuration Guide - Page 547

• 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 26-1. Figure 26-1. 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. Traffic Class (8 bits) The Traffic Class field deals with any data that needs special handling. These bits define the packet priority and are defined by the packet Source. Sending and forwarding routers use this field to identify different IPv6 classes and priorities. Routers understand the priority settings and handle them appropriately during conditions of congestion. IPv6 Routing | 547