End-User Knowledge: The DNS Flush

It happens a lot of the time:  Why can't I reach this website? Why is this site timing-out? How come this service isn't working?  It's frustrating to pinpoint why issues like this occur, but they often happen.  

The first thing you should always do when you have a computer issue is, don't panic.

Else you'll have this on your hands.

Anyways, what the DNS flush can do for you is clear away a pretty big mess.  It'll clear away any preset DNS entries in your system and provide default access to the sites/services you are trying to reach.

Quick Review:  

What is DNS?

DNS - Domain Name System

Devices on a network are identified by an IP address.  As users, you care not what an IP address is, but what that IP address is mapped to.  This is where DNS comes into play.  When you first type in an address to reach a website: (ex) http://www.google.com, typing in that address is called a DNS request.  

Basically, your computer is asking the world wide web, "hey, does anyone know a google.com?"  

Well, a DNS server essentially acts like a operator, it'll reply, "I found it and google.com is '74.125.225.84'"  Your computer completes the request, goes to 74.125.225.84, and you're on google.com. 

Your computer remembers this information in case you'd like to access the same site again, called DNS caching.  Typically, there is a certain length of time until your computer 'forgets' this mapping, however, it'll make a DNS request if it has forgotten.  

Back on point, sometimes that DNS cache or address memory bank gets corrupt or it's contents are affected by an application or service.  As a user, you'd notice an issue if you know for a fact you have an internet connection, but certain websites and services cannot load.  Here's where the DNS Flush comes into play.

In a Windows Command Prompt, that looks like this:

[C:\] ipconfig /flushdns
Windows IP Configuration
Successfully flushed the DNS Resolver Cache.
[C:\]

This simple command clears your DNS cache and prompts the computer to make a DNS request, thus providing your computer with a proper address which will resolve to the website you were trying to reach.

I'm not going to get into specifics with this post or begin to discuss DNS hierarchy, but this should give you a better idea as to what the DNS flush does for you.  

Lastly, I'd like to point out that rebooting your computer clears out the DNS.  So, while it's annoying that your IT Support Tech will tell you to reboot, it serves a bigger purpose which will likely correct the issue.

How to fix remotely - Terminal server has exceeded the maximum number of allowed connections.

How annoying is this message?  It seems every time I've run into this issue it's because some user incorrectly exited of the session and their session thinks it's still connected.  Well don't beat your head over this one, it's actually a pretty simple fix.

First make sure you are logged into the client computer as a domain Admin user.
command: net use /user:[username] \\servername
 ex:            net use  /user:GenericUser \\Generic-Server

                "Enter the password for 'GenericUser' to connect to 'Generic-Server':"

                       #if you typed in the right pass

                "The command completed successfully"

From here, we need to see which users have open sessions on the box.  To do this type the command:

query session /server:[servername]

Using the previous command displays which session ID's are currently logged into the client machine.  The next step is booting that user from the box.

reset session [ID] /server:[servername]

now if you run the query session command, you should see that the offending session ID has now been disconnected.

Alternative commands:

If you've been googled this issue and have seen commands such as: qwinsta, rwinsta, and logoff being used, these are alternative commands to what I listed.  You can substitute qwinsta for "query session" and substitute logoff for "reset session".  Everything else in the command stays the same. Rwinsta is another alternative for logoff or reset session, however, the session ID comes after the server name.  Listed below are examples of each alternative command being used:

qwinsta /server:[servername]

rwinsta /server:[servername] [sessionID]

logoff [sessionID] /server:[servername]

Event ID: 8003 Master Browser derp

short synopsis: disable the Computer Browser service on the offending PC.

“Event Type: Error
Event Source: MRxSmb
Event ID: 8003
Event Category: None
Description:
The master browser has received a server announcement from the computer XXX that believes that it is the master browser for the domain on transport NetBT_Tcpip_XXX-. The master browser is stopping or an election is being forced.“

This is simply a network configuration error and nothing more, so don't panic.  It's actually a fairly common error when you've got networked computers.  Frankly, I wouldn't consider it an error as an error states something is broke.  Think of this as an argument between children,  "This other computer thinks it's the Master browser, but I want to be!"

What's going on is Windows networking services, specifically MRxSmb, is having a difficult time trying to decide which computer should maintain this master browser list.  This browser list service provides a list of computer sharing resources in and on the domain.  Think of it as a list provided to workstations that can view network resources within your network neighborhood.

The first thing you need to take into consideration is: Is this a dedicated server on the network or are you running another machine with a Domain Controller?

Let's say it's a dedicated server on the network, then go to the machine specified in the event viewer text that is believing it is the Master Browser for the domain.
go into control panel->administrative tools->services then click on the Computer Browser option, click stop.

(what is? Computer Browser service - http://support.microsoft.com/kb/188001)

Also, double-check the registry settings by making sure the IsDomainMaster to False at:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Browser\Parameters\IsDomainMaster

 If you're running a Domain Controller, which you should ideally use as the "master browser", go to each of your workstations and disable the Computer Browser service. In addition, to ensure you've told your workstations not to search for a master browser, you can run a command line utility: BROWSTAT STATUS.  This tells you whether browsing is active, how many servers are on the domain, and what their names are.

This will resolve your issue.  However, as a disclaimer, only make registry edits if you are completely sure of what you are doing.  Also, after you make these changes, it is always in your best interest to reboot the machine.  If you are still having issues, you've either done something wrong, else your computers are not on the same subnet.

Understanding CALs

CALs, or Client Access Licenses, are often a confusing matter.  I've been working with them ever since I got started in IT, however, not until recently have I had a full understanding of when and where you'd use a CAL.  Not to mention, there are different types of CALs which add to the confusion.

Let me break down a few things for you:
-What's a CAL
-What CAL do I use?
-When not to use a CAL.

CAL,  a client access license. 
When you buy or manage a Windows server, it'll be licensed to end users or to businesses.  The CAL gives you rights to connect to a server, or server application. Most editions of server or a specific service, come with some CALs already.  This allows the software to be used by either a few users or a few computers.  The more users/computer, the more CALs required.  Think of it this way, one CAL per concurrent connection.

There are two types of CALs; a device and a user. 
User CALs allow one user to connect to a server or service.  Any user can connect, however, only one user may utilize the CAL at any given time.  Let's say you have SQL Enterprise 2k8 w/ a 5 CAL, then 5 users can utilize that service at the same time.

Device CALs allows one device to connect to the server or service.  Connections are limited by device, rather than user.  So if you have a lot of users and a small amount of devices, utilizing CALs for each of those devices is more cost-effective.

Core CALs, are special CALs offered by Microsoft via corporate licensing.  Core CALs include CALs for Microsoft Windows Server, Exchange, Systems Management Server, and Sharepoint.  Think of it as a suite of CAL offerings to license basic server components across your computers.  Less overhead equals less management of your CALs.  So if you're going to utilize many Microsoft services, look into Core CAL licensing.

Lastly, when don't you need a CAL?  When your users access the server anonymously or when they require privacy via authentication.  You do not need to add CALs for users who are authenticating.  If you are gearing your server or services for customers and not internal-employees, you'll want to utilize an External Connector.  An EC allows an unlimited number of outside users to access a server or service.  However, EC's should only be considered when you have a large customer-base because they are rather expensive.  If you have a smaller external user-base, CALs are a much more cost-effective solution.