The HTTP 400 Error

The HTTP 400 error translates to Bad Request. It can sometimes be seen when attempting a logon to a website unsuccessfully.

In short, the server cannot process your request - potentially due to malformed URLs, corrupted cookies or outdated DNS data.

You can try flushing the DNS cache as well:

ipconfig /flushdns

which should yield the output "Successfully flushed the DNS Resolver Cache" if successful.

ipconfig's DNS features

ipconfig /displaydns

displays the contents of the DNS Resolver Cache (also known as the DNS cache). 

The DNS cache is a temporary DNS storage on your device holding already visited domain names.

Stuff you might see in there include some complicated microsoft.com related addresses under Record Name. Record type of 1 signifies an IP address (IPv4). Record type 2 (also known as a AAAA record) is an IPv6 address.  Record type 5 is an MX record (mail exchange). MX records show where mail for a domain should be routed to. Multiple MX records may exist for a single domain. Time to live is the time in seconds for the cache entry to expire.

These records represent the content of a DNS reply.

Why Windows Networking ipv6 Rocks

To be a Windows configuration and networking uber-master, you must be fully familiar with the the command-line tools like ipconfig, route.exe and netsh. You must also aware and ready for the oncoming onslaught of IPv6, know why it is needed and also be reasonably au fait with the new IPv6 header format (similarities and differences with IPv4). You need to know what SSIDs are (easy, they are Service set ids used to identify 802.11 wireless networks).
Even then, you will only be skimming the surface of knowledge possessed by true Windows networking gymnasts.

The key beauty of v6 IP, is its incredibly ingenious and generous 128 bit source and destination IP addresses (FOUR TIMES THE SIZE OF IPv4), which can express over 10^38 possible combinations - amazing! Ubiquitous, interplanetary computing here we come!

IPv6 will form the basis of the IP-routing infrastructure of the 21st Centuramos. This is a certainty.

Here's ANOTHER super-cool fact about IPv6, it has standards-based security built in in the form of IPSec - ENCRYPTION SERVICES for IP NETWORK TRAFFIC. I know what you are thinking? How do I QUICKLY apply IPSec technology to secure traffic between client and server? There is some terminology to get familiar with before you start reading up on IPSec meaningfully. The first is L2TP (Layer Two Tunnelling Protocol).

IPv6 configuration is complicated by different types of addresses (G-L-S), for varying levels of GLOBALNESS and LOCALNESS. We have Global addresses (globally reachable on IPv6 portion of the Internet; these addresses typically begin with "2" or "3"), Link-local, used on a specific link (always begin with fe80), site-local, used within an organization's intranet, can be reused for different sites of an organization.

Praciticalites - To get help on ipconfig, open a command window and type ipconfig /?.

Now you can type:

ipconfig .. or...
ipconfig /all

You'll probably see rows like:
Wireless LAN adapter
Ethernet adapter Local Area Connection 2:
Ethernet adapter Local Area Connection 3:
Tunnel adapter Local Area Connection* 6:
Tunnel adapter Local Area Connection* 7:

You'll see IPv6 addresses are given before IPv4 addresses.

What is a tunnel adapter I hear you holler? some IPv6 transition technology, methinks...prepare to see a lot of these "transition technologies" going forward!