I found this site: dns crawler] Adding in the ip address: 2001:4898:e8:100b:98de:554a:9c3c:fbbf and the subnet mask 255.255.252.0, or /22, I get the netmask to be ffff:fc00:0:0:0:0:0:0 The calculator gives me: CIDR Block 2001:4898:e8:100b:98de:554a:9c3c:fbbf/22 That is the address that I had initially set, so it appears that it is already in CIDR format like it requires. <UnicastIpAddresses> <IpAddress wcm:action="add" wcm:keyValue="1">2001:4898:e8:100b:98de:554a:9c3c:fbbf/22</IpAddress> </UnicastIpAddresses>