Test TCP connectivity to a host:port from the server — bypasses browser CORS restrictions
google.com:443
github.com:22 (SSH)
github.com:443
1.1.1.1:53 (DNS)
20
21
22
23
25
53
80
110
143
443
465
587
993
995
1433
3306
5432
6379
8080
8443
9200
27017