You must enter correct network id and corresponding mask id for route or prefix. So called prefix or prefix id is just network id while prefix length is mask or network mask. You can use online subnet calculators to see network id or prefix id. In case of CCNA exam, you must figure out using piece of paper (I recommend using magic number method not binary method).
To start You must figure out network part and host part of particular address. Mask is what indicates where your network id stops and hosts start. Before subnetting, for all Classful networks (ones that are not subnetted) network id usually ends in 0. like ip route 10.0.0.0 255.0.0.0 or 192.168.1.0 /24 or 172.31.0.0 /16. In case of subnetting, we have easy subbnetting like 10.10.10.0 255.255.255.0, and hard ones like 10.10.10.12 255.255.255.252. or 192.168.10.64 255.255.255.224.. In any case, you must learn subnetting for Cisco certification exams. You can start with CCNA book from Cisco press and also find some videos on youtube.
Host routes are special routes that indicate end-host IP. easy to recognize because they all end with /32 (all 255s). So,
10.10.10.x 255.255.255.255 would work here (where x is any non-zero number).
Regards, ML
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