Domain Name System (DNS)
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The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names
assigned to each of the participants. Most importantly, it translates
domain names meaningful to humans into the numerical (binary)
identifiers associated with networking equipment for the purpose of
locating and addressing these devices worldwide. An often used analogy
to explain the Domain Name System is that it serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses. For example, translates to 192.0.32.10. |
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HOSTS file -- in the old days and still alive and well today
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contained a list of ip addresses for every computer on the internet, matched to the corresponding system names. it's just a text file that you can open with any text editor. HOSTS files still have their place in today's world. Lots of people place shortcut names in a HOSTS file to avoid typing long names in some TCP/IP applications. Yet even though HOSTS still has some use, for the most part we use the vastly more powerful DNS. A HOSTS file uses a flat name space basically just one big undivided list containing all names with no grouping whatsoever. In a flat name space, all names must be absolutely unique - no two machines can ever share the same name under any circumstances. A flat name space works fine on a small, isolated network, but not so well for a large org with many interconnected networks. To avoid naming conflicts, all its admins would need to keep track of all the names used throughout the entire corp network.
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DNS root servers
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a naming system sesigned to facilitate delegation. The top-dog DNS server is actually a bunch of powerful computers dispersed around the world and working as a team, known collectively as the DNS root servers or simply7 at the DNS root. The internet name of this computer team is "." -- "dot". DNS root has the complete definitive name resolution table, but most name resolution work is delegated to other DNS servers. Just below the DNS root in the hierarchy is a set of DNS servers called the top-level domain servers that handle what are known as the top level domain names. These are the famous COM, ORG, NET, EDU, GOV, MIL, AND INT.
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DNS hierarchical name space
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is an imaginary tree structure of all possible names that could be used within a single system. Works in a manner extremely similar to how your computer's file system works. The DNS name space is a hierarchy of DNS domains and indiv computer names organized into a tree like structure that we call a tree. Each domain is like a folder - a domain is not a single computer, but rather a holding space into which you can add computer names. At the top of a DNS tree is the root. The root is the holding area to which all domains connect, just as the root dir in your file sys is the holding area for all your folders. Indiv computer names more commonly called host names in the DNS naming convention fit into domains. In the pc you can place files directly into the root dir. The DNS world also enables us to add computer names to the root, but with the exception of a few special computers. Ea domain can have subdomains just as the folders on your pc file sys can have subfolders. You separate ea domain from its subdomains with a period. Characters for DNS domain names and host names are limited to uppercase and lowercase letters A-Z a-z, 0-9, and the hyphen (-). No other characters may be used.
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Fully Qualified Domain Name FQDN
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a complete DNS name, including the host name and all of its domains in order is called a FQDN and it's written out with the root on the far right, followed by the names of the domains in order added to the left of the root, and the host name on the far left.
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Authoritative DNS Server
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This single DNS server has a list of all the host names on the domain and their corresponding IP addresses. Also called Start of Authority or SOA.
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Name Servers NS
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Equally, a single DNS domain may have a single authoritative DNS server but a number of other DNS servers, known simply as name servers (NS) that are subordinate to the authoritative DNS server but all support the same domain. The SOA is a name server as well. Every DNS server, whether it's the SOA or just and NS, knows the name and address of the SOA as well as every other NS server in the domain. It's the SOA's job to make sure that all the other name servers are updated for changes.
Note that a DNS server does not have to be a member of a domain to be a name server for that domain.
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Cache-only DNS servers
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Cache-only DNS servers do not store any FQDNs and are only used to talk to other DNS servers to resolve ip addresses for dns clients.
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forward lookup zones
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the ip addresses and fqdns for the computers in a domain are stored in special storage area called forward lookup zones. Forward lookup zones are the most important part of any dns server. Every DNS forward lookup zone will have one SOA and at least one NS record. Forward lookup zone will have some number of A records. But there are a number of other records you may or may not see in your standard DNS Server.
Two common types:
Primary Zone are created on DNS srvr that will act as the SOA for that zone.
Secondary Zone are created on other DNS servers to act as backups for the primary zone. It's standard practice to have at least two DNS servers for any forward lookup zone...one primary and one secondary.
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NS records
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are all of the dns servers for [totalhome] -- note that totalhome has 2 dns servers.
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Canonical name (CNAME)
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record acts like an alias.
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MX records
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used exclusively by SMTP servers to determine where to send mail.
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A record
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The A records in the folder are the ip addresses and names of all the systems on the x domain.
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Reverse lookup zones
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enables a sys to determine an FQDN by knowing the ip address; that is, it does the exact reverse of what DNS normally does! Reverse lookup zones take a network ID, reverse it, and add the term in-addr-arpa to create the zone. A few low-level functions (like mail) and some security programs use reverse lookup zones, so DNS servers provide them. In most cases the DNS server will ask you if you want to make a reverse lookup zone when you make a new forward lookup zone. When in doubt, make one. If you don't need it, it won't cause any trouble.
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Active Directory-integrated zone
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Win 2000 Server and beyond Windows only type of forward lookup zone. DNS works beautifully for any tcp/ip app that needs an ip address of another pc, but it has one glaring weakness: you need to add A records to the DNS server manually. This can be a problem. Interestingly, it was a throwback to an old MS Win protocol that fixed this and a few other problems all at the same time. Even though tcp/ip was available, back in the 80s MS popularized another networking protocol called NetBIOS /NetBEUI. It was simplistic compared to tcp/ip. It had a very simple naming convention (netbios part) that used broadcasts. When a pc booted up it just told the world its name. Netbios / netbeui was suitable only for small networks. It provided no logical addressing like ip addresses; you just had to remember the netbios name and mac address. Netbios /Netbeui as almost exclusively used to share folders and printers. Instead of dumping Netbeui protocol kept it running on top of ip. In essence MS created its own name resolution protocol that had nothing to do with DNS! Technically NetBIOS no longer exists, but the overlying protocol that used it to share folders and printers is still very much alive.
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Common Internet File System (CIFS)
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In computer networking, Server Message Block (SMB, also known as Common Internet File System, CIFS) operates as an application-layer network protocol[1] mainly used to provide shared access to files, printers, serial ports, and miscellaneous communications between nodes on a network. It also provides an authenticated inter-process communication mechanism. Most usage of SMB involves computers running Microsoft Windows, where it is often known as "Microsoft Windows Network". CIFS makes most small networks live in a two-world name resolution system.
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Three types of groups: Workgroups, Windows Domain and Active Directory
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Workgroup is just a name that organizes a group of computers. This does little more than organize all the computers in the network / my network places folder. Windows domain is a group of computers controlled by a computer running Windows Server. This server computer is configured as a domain controller. You would then have your pcs join the domain. All the computers within a domain authenticate to the domain controller when they log in. Note that Win domain is not the same as a DNS domain. Wins domains now use DNS for their names. A Wins domain must have a true DNS name. DNS domains that are not on the Internet should use the top level name .local (although you can cheat and not use it).
Active Directory is an organization of related computers that shares one or more Windows domains. Windows domain controllers are also DNS servers. The beauty of Active Directory is that there's no single momain controller; all of the domain controllers are equal partners and any domain controller can take over if one domain controller fails.
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Active Directory-Integrated Zones
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A standard primary zone stores the DNS info in test files. You then need seondary zones on other DNS srvrs to bu that srvr. If the primary dns srvr goes down, the secondary servers can resolve fqdns, but you can't add any new records. Nothing can be updated until the primary DNS server comes back up. In an Active Directory-integrated zone, all of the domains controllers (which are all also DNS servers) are equal and the whole DNS sys is not reliant on a single DNS server. Last, Wins DHCP srvrs will automatically update all the client info in the Active Directory-integrated zone. If a computer gets a DHCP lease, the DHCP server tells the DNS server that it has new DNS info. Non-Wins sys can only do this using Windows clients (like Samba).
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NSLOOKUP
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name server lookup command -- it's a handy tool that advanced techs use to query the functions of DNS servers. You can (assuming you have the permission) query al types of info from a DNS server and ghange how your sys uses DNS. While most of these cmds are far outside the scope of CompTIA...there are a few places where NSLOOKUP makes for a great basic tool. Just running it alone gives you the ip address and the name of your default DNS server. If you got an error at this point, perhaps a "server not found", you would know that either your primary DNS was down or you might not have the correct DNS server info in your DNS settings. You can attach to any DNS server by typing server, followed by the ip address or the domain name on the DNS server: > server x
Default Server: x
Addresses: 192.168.4.157, 192.168.4.156.
Note that in UNIX/Linus DIG is very similar to NSLOOKUP.
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LMHOSTS
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a special text file that contains a list of the NetBIOS names and corresponding IP addresses of the host systems on the network. The LMHOSTS file works exactly the same way as the DNS HOSTS file. Although MS still supports LMHOSTS file usage, and every Wins sys has an LMHOSTS file for backward compatibility, networks that still need NetBIOS support will usually run Windows Internet Name Service (WINS) servers for name resolution. WINS servers let NetBIOS hosts register their names with just the one server, eliminating the need for broadcasting and thereby reducing NetBIOS overhead substantially. You can find an LMHOSTS.SAM file on your Windows system. There are only 2 good reasons to use a WINS server: 1. to reduce overhead from broadcasts; and 2. to enable NetBIOS name resolution across routers. The WINS server enables NetBIOS to function in a routed network. IP routers are programmed to kill all broadcasts. While newer Windows clients will just register directly with the WINS server, older (pre-Win95) Wins sys will still try to broadcast. To get around this problem, you can configure a sys to act as a WINS proxy agent, forwarding WINS broadcasts to a WINS server on the other side of the router.
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WINS Server
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with WINS servers the bottom line is larger or routed networks that run NetBIOS still need them. As long as NT and Win 9x systems are out there running NetBIOS, don't be surprised to find that some system somewhere is running a WINS server.
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NETSTAT
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runing NETSTAT with no options shows you all the current connections to your system; look for a connection here that isn't working with an application such as a broken app or a sneaky app running in the background;- run netstat -s option displays several statistics that can help you diagnose problems. Ex. if the display shows you are sending but not receiving, you almost certainly have a bad cable with a broken receive wire.
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Configuring WINS Clients
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you only need to configure the ip address of a WINS server in its WINS settings under Network Properies. From now on, the Windows sys will look for a WINS server to register its NetBIOS name. If it finds a WINS server, it will register its NetBIOS name to the WINS server; if it doesn't, it will automatically start broadcasting its NetBIOS name. You can add WINS info to DHCP if necessary, so unless you're running static IP addresses, you may never have to enter anything into your Windows clients to get WINS to work.
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NBSTAT
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use this program to help deal with NetBIOS problems. It will do a number of jobs, -c switch tells nbtstat to check the current NetBIOS name cache; you can use nbtstat to see if the WINS server has supplied inaccurate addresses to a WINS client.
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net view command
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if you're using netbios use this command to see if the other local systems are visible.
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Diagnose to the gateway
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if you can't get out to the internet, check to see if you can ping the router. Remember, the router has two interfaces, so try both: first the local interface (the one on your subnet), and then the one to the internet. If you can't PING the router, either it's down or you're not connected to it. If you can only PING the near side, something in the router itself is messed up.
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Diagnose to the Internet
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If you can PING the router, it's time to try to PING something on the Internet. If you can't PING one address, try another - it's always possible that the first place you try to PING is down. If you still can't get through, you can try to locate the problem using the TRACERT (trace route) command. It will mark out the entire route the PING packet traveled btw you and whatever you were trying to PING and, even better, will tell you where the problem lies.
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