Unlike in IPv4, IPv6 [[router (computing)|router]]s (intermediate nodes) never fragment IPv6 packets. Packets exceeding the size of the [[Maximum transmission unit]] (or MTU) of the destination link are dropped and this condition is signaled by a ''Packet too Big'' [[ICMPv6]] type 2 message to the originating node, similarly to the IPv4 method when the ''[[IPv4#Flags|Don't Fragment'']] bit is set.<ref name=rfc8200 /> End nodes in IPv6 are expected to perform [[Path MTU Discovery]] to determine the maximum size of packets to send, and the upper-layer protocol is expected to limit the payload size.
End nodes in IPv6 are expected to perform [[Path MTU Discovery]] to determine the maximum size of packets to send, and the upper-layer protocol is expected to limit the payload size. However, if the upper-layer protocol is unable to do so, the ''sending host'' may use the ''[[IPv6 packet#Fragment|Fragment'' extension header]] in order to perform end-to-end fragmentation of IPv6 packets. Any data link layer conveying IPv6 data must at least be capable of delivering an IP packet containing up to 1280 bytes, withoutthus the needsending toendpoint invokemay limit its packets end-to-endfragmentation1280 atbytes theand IPavoid layerany need for [[Path MTU Discovery]] or fragmentation.
