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ok.. so if the host application doesn't know the IP then it will know FQDN and resolve it to IP. So in this scenario a DNS help shall be required or NATing device also can work as a DNS?
Correct, the sending device has to somehow "know" the address of the recipient. It might be its IP or it might be by logical name (e.g. supportforums.cisco.com).
If NAT is involved, it may need to also NAT the DNS query and response, but that doesn't mean the NAT device, itself, is doing DNS.
