Country Code Top Level Domains
There are two types of top-level domains: generic and country code. Generic Top Level Domains (gTLD) are used on a global basis and include tlds like Com, Net, org, Info, biz, Aero, etc.
Country code Top Level Domains (ccTLD) are meant for use by individual countries, as they deem necessary. Examples include .US, .UK, .AU, .IN, etc.
Some country code domains are open to registration on a global basis. However most of the country code domains are restricted.
Whois Servers for ccTLDs
The registries for country code TLDs maintain their own whois servers. Here are a few examples
in: whois.inregistry.net nu: whois.nic.nu
Port 43 Whois Server for a specific Countries
You can find the official whois server (if available) for a specific country code by querying IANA (Internet Assigned Numbers Authority) whois server at whois.iana.org.
For example, querying whois.iana.org for IN returns the following...
Registration Date: 01-January-1985
Last Updated Date: 04-August-2006
URL for registration services: http://www.registry.in
Whois Server (port 43): whois.inregistry.net
IP Address: 18.104.22.168 2001:502:d399:0:0:0:0:1