The advertise high-metrics feature, when enabled on a device, advertises it with the metric as maxLinkMetric-1 value (i.e. 16777214). This allows the router to be used as a last resort if no other path is available.

This feature helps in figuring out if there are multiple nodes in the network with the same System-ID. A non-unique node leads to the failure of all subsequent functions of the IS-IS protocol, like LSP origination (leading to LSP constant flooding issue), SPF calculation and so on.