Processing Labeled IPv4 Datagrams which are Too Big
If a labeled IPv4 datagram is "too big", and the DF bit is not set in
its IP header, then the LSR MAY silently discard the datagram.
Note that discarding such datagrams is a sensible procedure only if
the "Maximum Initially Labeled IP Datagram Size" is set to a non-zero
value in every LSR in the network which is capable of adding a label
stack to an unlabeled IP datagram