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IPv6 Headers
The IPv6 header has a fixed length of 40 bytes. This fixed length 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 shown in the following illustration.
Figure 58. IPv6 Header Fields
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
IPv6 Routing
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