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What is the difference between packet fragmentation in IPv4 and IPv6?

In this Q&A, our IPv6 expert explains how packet fragmentation differs in IPv6 compared to IPv4.

QUESTION: What is the difference between packet fragmentation in IPv4 and IPv6?

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One of the innovations introduced by IPv6 is the elimination of hop-by-hop packet fragmentation. With the new protocol, fragmentation is managed at the ends by means of a special extension header.

More specifically, there are two main differences: Difference one is the fields for handling fragmentation are not in the basic IPv6 header but are put into an extension header if fragmentation is required. This makes IPv6 fragmentation lean because this fragmentation extension header is only inserted in the packet, if fragmentation needs to be done. Difference two is that IPv6 routers do not fragment anymore. Fragmentation has to be done by the source host. He will evaluate the packet size by using Path MTU discovery.

This was first published in January 2009

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