The format of the data in the file:
StandardBER standard SNMP ASN.1 BER
bulkBinary a binary format specified with this MIB
bulkASCII a human-readable form of bulkBinary
variantBERWithCksum ASN.1 BER encoding with checksum
variantBinWithCksum a binary format with checksum
A given system may support any or all of these.