OID value: 1.3.6.1.2.1.4.20.1.5
OID description:
ipAdEntReasmMaxSize OBJECT-TYPE
              SYNTAX  INTEGER (0..65535)
              ACCESS  read-only
              STATUS  mandatory
              DESCRIPTION
                      "The size of the largest IP datagram which this
                      entity can re-assemble from incoming IP fragmented
                      datagrams received on this interface."
              ::= { ipAddrEntry 5 }
See also the OID Repository website reference for 1.3.6.1.2.1.4.20.1.5