dnswalk 是 Kali linux和 Parrot Security OS 內建的工具，可以使用這個工具來搜尋 subdomain。
- 操作環境 Parrot Security OS
-r Recursively descend sub-domains of the specified domain.
-a Turn on warning of duplicate A records.
-d Print debugging and 'status' information to stderr. (Use only if redirecting stdout).
-m Perform checks only if the zone has been modified since the previous run.
-F Perform "fascist" checking. When checking an A record, compare the PTR name for each IP address with the forward name and report mismatches.
-i Suppress check for invalid characters in a domain name.
-l Perform "lame delegation" checking. For every NS record, check to see that the listed host is indeed returning authoritative answers for this domain.