This is the rn (Relative Name), the single naming segment that, appended to its parent's dn, forms the full dn for this one instance of a contiguous IPv6 address range (block) defined within an IPv6 management IP pool, the from/to boundaries UCS Manager draws individual IPv6 addresses from. UCS Manager derives this segment automatically from the object's own defining attribute (such as an address, index, or configured name), so seeing a distinctive rn like this is how you tell one IpV6Block row apart from every sibling row under the same parent. For this class the rn typically looks like 'block-2001:db8::10-2001:db8::50'.