What does the command 'no auto-summary' do in EIGRP?

The command 'no auto-summary' is used in Enhanced Interior Gateway Routing Protocol (EIGRP) to disable automatic summarization of routes. By default, EIGRP summarization automatically occurs at network boundaries, where classful networks are used. This means that if a router has several subnets, it would advertise only the classful address (for example, a single network address) instead of all the specific subnet routes.

By entering 'no auto-summary', the router will advertise the more specific subnet routes rather than consolidating them into a single classful route. This is particularly important in discontiguous networks or when subnets of the same major network reside on different segments, as automatic summarization can lead to routing issues and connectivity problems. Disabling this feature ensures that more precise routing information is shared, which can enhance efficiency and route management.