IPv6 introduces significant changes to how fragmentation is handled compared to IPv4, especially as it relates to intermediate devices such as routers.

These changes affect the performance and efficiency of network traffic. In IPv6, fragmentation is handled differently to reduce the load and complexity on routers and improve overall network performance.

How Fragmentation Works in IPv6:

1. Fragmentation by the Issuing Host: In IPv6, routers do not fragment packets. If a packet needs to be fragmented to pass over a link with a smaller MTU (Maximum Transmission Unit), the router discards the packet and sends an ICMPv6 “Packet Too Large” message to the sending host. This tells the sender to fragment the packets before forwarding them.
2. Router Simplification: By moving the responsibility for fragmentation to the sending host, IPv6 eliminates the need for routers to handle fragmentation. This reduces the processing load on routers, simplifying packet processing and potentially improving the speed of data transmission over the network.
3. Path MTU Discovery: IPv6 uses Path MTU Discovery more comprehensively. This process allows the sending host to determine the smallest MTU along the path to its destination to avoid mid-path fragmentation. This optimizes performance by ensuring that packets are the correct size from the moment they leave the host, reducing the possibility of discards and retransmissions.

Comparison with IPv4:

In IPv4, both hosts and routers can fragment packets when the packet size exceeds the MTU of the link. Routers performing fragmentation must maintain the state of the fragments and sometimes reassemble them, which can lead to an increase in CPU usage and a reduction in overall performance, especially on congested networks or on routers with high traffic.

Impact on Performance:

• Load Reduction on Routers: By eliminating router workload fragmentation in IPv6, these devices can process traffic more quickly and with less overhead, theoretically improving network performance.
• Host Responsibility: As the load on routers decreases, hosts must be smarter about how they handle their data transmissions, which could mean greater resource usage on the host, especially in situations where fragmentation is necessary.

Conclusion:

Defragmentation on IPv6 hosts, by avoiding fragmentation on intermediate devices, does have the potential to offer better performance compared to IPv4.

This change in fragmentation management reflects a general design philosophy in IPv6: simplify routers to improve network efficiency and move more logic and responsibility to the edges of the network.