OID value: 1.3.6.1.2.1.4.21
OID description:
ipRouteTable OBJECT-TYPE
              SYNTAX  SEQUENCE OF IpRouteEntry
              ACCESS  not-accessible
              STATUS  mandatory
              DESCRIPTION
                      "This entity's IP Routing table."
              ::= { ip 21 }
See also the OID Repository website reference for 1.3.6.1.2.1.4.21