As was discussed in Section [188.8.131.52], a router MUST support IP fragmentation.
A router MUST NOT reassemble any datagram before forwarding it.
A few people have suggested that there might be some topologies where reassembly of transit datagrams by routers might improve performance. The fact that fragments may take different paths to the destination precludes safe use of such a feature.
Nothing in this section should be construed to control or limit fragmentation or reassembly performed as a link layer function by the router.
Similarly, if an IP datagram is encapsulated in another IP datagram (e.g., it is tunnelled), that datagram is in turn fragmented, the fragments must be reassembled in order to forward the original datagram. This section does not preclude this.