Routing - 'subnets' keyword for redistribution
When performing redistribution, the redistribute command can include the subnets keyword. This keyword is used to ensure that all subnets, including directly connected ones, are included in the redistribution process.
Without the 'subnets' keyword, only classful networks are redistributed, meaning only routes that match the exact classful network statement will be included.
Using subnets guarantees that all routes, including subnetted routes and connected addresses, are redistributed.
Links:
https://forum.networklessons.com/t/troubleshooting-ospf-route-advertisement/1191/26?u=lagapidis
https://networklessons.com/cisco/ccie-routing-switching/introduction-to-redistribution