The loopback and 6to4 tunnel interfaces have the following OIDs for ifAdminStatus and ifOperStatus:
.18.104.22.168.22.214.171.124.1.2.1 = STRING: "lo" (loopback)
.126.96.36.199.188.8.131.52.1.2.2 = STRING: "sit0" (6to4 tunnel)
.184.108.40.206.220.127.116.11.1.7.1 = INTEGER: 1
.18.104.22.168.22.214.171.124.1.7.2 = INTEGER: 2
.126.96.36.199.188.8.131.52.1.8.1 = INTEGER: 1
.184.108.40.206.220.127.116.11.1.8.2 = INTEGER: 2
If the ifAdminStatus or ifOperStatus are queried they can return a value of either 1 (up) or 2 (down). These interfaces are created by the operating system kernel, the sit0 is not used by the PCS/PPS system and the lo interface is used internally and is not accessible externally.