This read-only Integer32 is the 32-bit sum of the LS checksums of all type-11 LSAs in the external link-state database, per its description, providing a cheap way to detect that something in that LSA set changed without walking the whole database. Because any single LSA content change alters its checksum and thus this running sum, comparing this value between polling intervals, or between two routers that should hold an identical AS-scope opaque LSA set, is a fast consistency check. An engineer suspecting an opaque-LSA database desync between two routers in the same OSPF domain would compare this checksum sum across both routers rather than dumping and diffing the entire LSA set.