IPv6 does not allow packet fragmentation throughout the internetwork. Only sending hosts are allowed to fragment. Routers are not allowed to fragment packets. RFC 2460 specifies that the MTU of every link in an IPv6 address must be 1280 bytes or greater. RFC 1981 recommends that nodes should implement IPv6 path MTU discovery to determine whether any paths are greater than 1280 bytes. ICMPv6 packet-too-big error messages determine the path MTU. Nodes along the path send the ICMPv6 packet-too-big message to the sending host if the packet is larger than the outgoing interface MTU.