Maximum transfer unit (MTU) for this sham link. This is the maximum packet size in bytes for packets sent over the sham link. This size excludes link layer headers but includes IP headers and higher-level headers. Normally, DC-OSPF will limit sent PDUs (protocol data units) to less than or equal to this size. However, if DC-OSPF cannot construct a valid OSPF 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.