a3ComDvmrpMospfIpMask 1.3.6.1.4.1.43.2.28.2.3.1.2

This is subnet mask associated with a3ComDvmrpMospfIpAddr. It is a number of contiguous leading 1s, i.e. if the value is 1, it indicates the subnet mask is 128.0.0.0, or if the value is 8 then the subnet mask is 255.0.0.0.