Maximum transfer unit (MTU) for the network interface.
This is the maximum packet size in bytes for packets sent over
the network interface. This size excludes link layer headers
but includes IP headers and higher-level headers.
Normally, OSPF limits sent PDUs (protocol data units) to less
than or equal to this size. However, if OSPF cannot construct
a valid PDU smaller than or equal to this size, then it will
send the smallest valid PDU and assume that the IP stack will
fragment the packet.