A reference to MIB definitions specific to the particular
routing protocol which is responsible for this route, as
determined by the value specified in the route's
cIpForwardProto value. If this information is not present,
its value should be set to the OBJECT IDENTIFIER { 0 0 },
which is a syntactically valid object identifier, and any
implementation conforming to ASN.1 and the Basic Encoding
Rules must be able to generate and recognize this value.