<P> Routers do not fragment IPv6 packets, as they do for IPv4 . Hosts are "strongly recommended" to implement Path MTU Discovery to take advantage of MTUs greater than the smallest MTU of 1280 octets . A node may use the IPv6 Fragment header to fragment the packet at the source and have it reassembled at the destination (s). </P> <P> Since July 2017, the Internet Assigned Numbers Authority (IANA) is responsible for registering all IPv6 parameters that are used in the various IPv6 headers . </P> <P> The fixed header starts an IPv6 packet and has a size of 40 octets (320 bits). It has the following format: </P> <Dl> <Dd> <Table> Fixed header format <Tr> <Th> Offsets </Th> <Th> Octet </Th> <Th_colspan="8"> 0 </Th> <Th_colspan="8"> </Th> <Th_colspan="8"> </Th> <Th_colspan="8"> </Th> </Tr> <Tr> <Th> Octet </Th> <Th> Bit </Th> <Th> 0 </Th> <Th> </Th> <Th> </Th> <Th> </Th> <Th> </Th> <Th> 5 </Th> <Th> 6 </Th> <Th> 7 </Th> <Th> 8 </Th> <Th> 9 </Th> <Th> 10 </Th> <Th> 11 </Th> <Th> 12 </Th> <Th> 13 </Th> <Th> 14 </Th> <Th> 15 </Th> <Th> 16 </Th> <Th> 17 </Th> <Th> 18 </Th> <Th> 19 </Th> <Th> 20 </Th> <Th> 21 </Th> <Th> 22 </Th> <Th> 23 </Th> <Th> 24 </Th> <Th> 25 </Th> <Th> 26 </Th> <Th> 27 </Th> <Th> 28 </Th> <Th> 29 </Th> <Th> 30 </Th> <Th> 31 </Th> </Tr> <Tr> <Th> 0 </Th> <Th> 0 </Th> <Td_colspan="4"> Version </Td> <Td_colspan="8"> Traffic Class </Td> <Td_colspan="20"> Flow Label </Td> </Tr> <Tr> <Th> </Th> <Th> 32 </Th> <Td_colspan="16"> Payload Length </Td> <Td_colspan="8"> Next Header </Td> <Td_colspan="8"> Hop Limit </Td> </Tr> <Tr> <Th> 8 </Th> <Th> 64 </Th> <Td_colspan="32"> Source Address </Td> </Tr> <Tr> <Th> 12 </Th> <Th> 96 </Th> </Tr> <Tr> <Th> 16 </Th> <Th> 128 </Th> </Tr> <Tr> <Th> 20 </Th> <Th> 160 </Th> </Tr> <Tr> <Th> 24 </Th> <Th> 192 </Th> <Td_colspan="32"> Destination Address </Td> </Tr> <Tr> <Th> 28 </Th> <Th> 224 </Th> </Tr> <Tr> <Th> 32 </Th> <Th> 256 </Th> </Tr> <Tr> <Th> 36 </Th> <Th> 288 </Th> </Tr> </Table> </Dd> </Dl>

What is the role of the next header field in ipv6