IF-MIB (RFC 2863)

The following interface types are presented in the ifTable:

ethernetCsmacd(6): for all Ethernet-like interfaces, regardless of speed, as per RFC 3635
ds1(18): DS1-MIB (applicable only to device's supporting digital interfaces)
voiceFXO(101): Voice Foreign Exchange Office (applicable only to device's supporting FXO interfaces)
voiceFXS(102): Voice Foreign Exchange Station (applicable only to device's supporting FXS interfaces)

The numbers in the brackets above refer to the IANA's interface-number.