The IPv6 header of the IPv4-translated packet in MAP-T can be up to 28 bytes larger than the IPv4 header (40-byte IPv6 header plus 8-byte fragmentation header versus 20-byte IPv4 header). In the case where the IPv4-to-IPv6 translated packet is larger than the IPV6 MTU, the original IPv4 packet is fragmented so that the size of the translated IPv6 packet is within IPv6 MTU. IPv6 packets are never fragmented, although they may contain the fragmentation header that carries fragmentation information related to the original IPv4 packet/fragment.
The IPv6 MTU in the VSR is configurable for each MAP-T domain. The L2 header is excluded from the IPv6 MTU.