The aging timeout in seconds. NT_IPM keeps value that Router level gave. This is high priority value for aging timeout.
Sources for this description
Multiple manufacturers; see the original MIB MIB copies (LibreNMS/Observium Community)Dell MIB copies (LibreNMS/Observium Community)D-Link official switch MIBsNetdisco MIB archive copiesNETGEAR official product and EOL MIB downloads