DNS

DNS Servers Open to Public Query

This is not an exhaustive list of publicly accessible DNS servers. There are more, those listed below are a subset, and may be better or worse than others.

IP Address	Provider	Location
8.8.8.8	Google	Global (routed via Anycast)
8.8.4.4	Google	Global (routed via Anycast)
156.154.70.1	DNSadvantage	[Global http://www.dnsadvantage.com/dnsadv/node_locations.html]
156.154.71.1	DNSadvantage	[Global http://www.dnsadvantage.com/dnsadv/node_locations.html]
208.67.220.220	OpenDNS	[Global, mainly US http://www.opendns.com/technology/network-map/] (routed via Anycast)
208.67.220.222	OpenDNS	[Global, mainly US http://www.opendns.com/technology/network-map/] (routed via Anycast)
4.2.2.1	Level 3	Probably global (routed via Anycast)
4.2.2.2	Level 3	Probably global (routed via Anycast)
194.72.9.34	BT	UK
194.72.9.34	BT	UK

Sources: http://theos.in/windows-xp/free-fast-public-dns-server-list/

NSLookup

NSLookup is a Name Server Lookup/Query tool which exists in both Unix and Windows distributions, and generally speaking, functionaly the same regardless of which version you're using. To start, run nslookup from the command line.

Command	Description
server	Displays the DNS server(s) currently being used by nslookup
server 8.8.4.4	Changes the DNS server being used/queried to 8.8.4.4
host.domain.com	Attempts to resolve host.domain.com against current DNS server
109.123.76.85	Attempts a reverse lookup for IP 109.123.76.85 against current DNS server
set q=mx	Set query type to MX (subsequent queries will look for Message Exchange (email) records)
set q=all	Set query type back to all records
exit	Quit nslookup

For example, to find the email exchange servers for a particular domain...

> set q=mx
> microsoft.com
Server:  [8.8.4.4]
Address:  8.8.4.4

Non-authoritative answer:
microsoft.com   MX preference = 10, mail exchanger = mail.messaging.microsoft.com
>