This read-create object is the subnet mask applied to a packet's source address before it is compared to rsIpAccessListSrc, with mask bits set to 1 marking the significant address bits. Admins must supply a valid mask consisting of a single contiguous block of leading ones, since an invalid mask makes the match logic ambiguous. For example, setting rsIpAccessListSrcMask to 255.255.255.0 makes the rule match on the source address's /24 network rather than the exact host address.