Resolution of Network address

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I have a captured file. When I enable "Resolve Network Addresses" I can see the names in the "Source" and "Destination" field. When I disable the option the IP addresses are seen. This is expected. However, my question is how does it resolve the IP addresses ? In command window when I do "nslookup <captured ip="">" one of them works, the other one does not return any name. The how does wireshark resolve both of those?

THANKS