IPv6 and Fragmentation
The essential change between IPv4 and IPv6 is that in IPv6 the Don’t-Fragment-bit is always on. And because it’s always on, it’s not explicitly contained in the IPv6 packet header (see Figure 3). There is only one fragmentation flag in the Fragmentation Header, the “More Fragments” bit, and the other two bits are reserved. The other change was that the packet identifier size was doubled in IPv6, using a 32-bit packet identifier field.
An IPv6 router cannot fragment an IPv6 packet, so if the packet is too large for the next hop the router is required to generate an ICMP6 Type 2 packet, addressed to the source of the packet with a Packet Too Big (PTB) code, and also providing the MTU size of the next hop. While an IPv6 router cannot perform packet fragmentation, the IPv6 sender may fragment an IPv6 packet at the source.
An IPv6 router cannot fragment an IPv6 packet, so if the packet is too large for the next hop the router is required to generate an ICMP6 Type 2 packet, addressed to the source of the packet with a Packet Too Big (PTB) code, and also providing the MTU size of the next hop. While an IPv6 router cannot perform packet fragmentation, the IPv6 sender may fragment an IPv6 packet at the source.
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