How IPV6 handles Fragmentation
Routers handle fragmentation in IPv4 which cause variety of processing performance issues.
IPv6 routers no longer perform fragmentation. IPv6 host use a discovery process [Path MTU Discovery] to determine most optimum MTU size before creating end to end session.
In this discovery process, the source IPv6 device attempts to send a packet at the size specified by the upper IP layers [i.e TCP/Application].
If the device receives an “ICMP packet too big” message, it informs the upper layer to discard the packet and to use the new MTU.
The “ICMP packet too big” message contains the proper MTU size for the pathway.
Each source device needs to track the MTU size for each session.
How MTU works in IPV6
MTU is the largest size datagram that a given link layer technology can support [i.e HDLC]
Minimum MTU for IPv4 is 68 Octet and for IPv6 1280 Octet.
Most efficient MTU for IPv4 is 576 and 1500 for IPv6.
How to determine the maximum size of IPv6 datagram...
The maximum size of IPv6 datagram will be determined by two factor:
Maximum Transmission Unit (MTU) of intermediate nodes [L2 link technology can support i.e HDLC].
Payload length of IPv6 header which is 16 bit so normal payload can not be larger then 64k octets.
Jumbogram can increase IPv6 datagram size larger then 64k octets. But they need special processing on each hop since they are oversize.
One of two uses of hop-by-hop option header is Jumbogram.
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