Packet format IPv6
ipv6 packet header
an ipv6 packet has 2 parts: header , payload.
the header consists of fixed portion minimal functionality required packets , may followed optional extensions implement special features.
the fixed header occupies first 40 octets (320 bits) of ipv6 packet. contains source , destination addresses, traffic classification options, hop counter, , type of optional extension or payload follows header. next header field tells receiver how interpret data follows header. if packet contains options, field contains option type of next option. next header field of last option, points upper-layer protocol carried in packet s payload.
extension headers carry options used special treatment of packet in network, e.g., routing, fragmentation, , security using ipsec framework.
without special options, payload must less 64kb. jumbo payload option (in hop-by-hop options extension header), payload must less 4 gb.
unlike ipv4, routers never fragment packet. hosts expected use path mtu discovery make packets small enough reach destination without needing fragmented. see ipv6 packet fragmentation.
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