Whois queries are done on remote port 43. Initially whois queries were done using a UDP port but this was changed to TCP. If you are using a firewall, and would like to perform whois queries, you need to configure a rule in your firewall that wlll allow connections to this remote port.
For example, in ISA Server Whois exists already in the Protocol Definitions and you can use it in a Protocol Rule to allow such connections. Or you can add a rule in IP Packet Filters as follows:
- In Filter Type check 'Custom'
- IP protocol = 'TCP'
- Direction = Outbound
- Local Port = Dynamic
- Remote Port = Fixed Port
- Remote Port number = 43