Single Server Whois

The single server whois can only query one server after the other. You can only submit one query at the time.

Multi Server Whois

The multi server whois can query multiple servers and it is possible to submit additional queries while other answers are pending.

Multiple queries: Whois query #1 and #2 has already got an answer, query #3 is still waiting.

Non-blocking queries: add more queries while other query results are pending. No waiting.

Whois Servers

There are a lot of Whois servers. Each server 'knows' only a limited scope. So users need to ask the corresponding whois server to get a valid answer. The german .de-whois server has only knowledge about the .de domains. Asking a .com domain or a IP number will result in an error message. So theoretically you need to ask (and know) the matching server. A solution are 'meta whois server' like whois.thur.de: like meta search engines they pass the query along to the matching server.

By default 3d Traceroute auto-installs these servers:

whois.thur.de
whois.internic.net
whois.crsnic.net
whois.nic.uk
whois.aunic.net
whois.cdnnet.ca
whois.ripe.net

You can add, modify and remove servers. A port number can be added by server:port.