Handout by huanghengdong


									Networking Project                                                                              EBM

                                   (Domain Name Server)

   DNS:

A serves that identifies the IP address or it identifies a web page in URL. Every domain
name ends with (TLD) which is short of top level domain name, either from a country
code (two characters) or generic names (three or more characters).

An Internet service that translates domain names into IP addresses. For example, the
DNS converts the name of a website (www.example.com) into IP address (

   Root DNS Server:
Is the top of the hierarchy containing all organizational domain zone names and it is a
server installed to be the source for determining names for a hierarchical namespace.

   Address DNS resolution
    Resolution occurs when a client queries a name server to get the IP address. It is a
    procedure used to resolve the IP address form Domain Name

        DNS Resolution similarity:

                    Looking up Phone Number:

             1. Get the phone directory of the right city
             2. People are listed by last name
             3. Narrow it to the first name.
             4. The phone number allows you to communicate over the phone, not the
         person’s name. As when you search for NSLookup.

    DNS Resolution Scenario:

                    How DWC use DNS:

                        Student local client asks the local name server for the IP address of
                        DWC had two Name servers “NS1, NS2”. NS1 is primary, NS2 is
                        NS2 responsible of all queries because NS1 is critical. However if NS2
                         has a problem. Then it automatically switched the query to NS1.
                        The local NS do not know the IP address of yahoo.com. So it asks AB
                         server, if not then ask Etisalat server. Also Etisalat ask other server till

Amal200221480, Buthaina 200224233, Latifa 200221763, Maryam. S 200221977                        HD2
Networking Project                                                                           EBM

                         get IP address of yahoo.com. Afterward it tells to the local name
                        The local name server passes the IP address of yahoo.com to the local
                        If the local client query once again for yahoo.com, it will get it in NS2
                         because it catches before. As a result of this, NS2 has listed of
                         websites or e-mail that the client used before.
                        Other big companies use this DNS Resolution scenario

     Reverse DNS Resolution:
    A procedure used to resolve a domain name from an IP address

   Why Reverse DNS useful?

    1. Tracing traffic that goes through Firewalls
    2. Documentation
    3. E-mail server legalization

   NS Lookup:

    NSLookup is a tool or service to find information that DNS client needs. The
    NSlookup helps to find the domain name to IP address. The queries job is to find the
    name for DNS server.

   SOA:

    1. The SOA resource record contains the following information:
       Source host - The host where the file was created.

    2. Contact e-mail - The e-mail address of the person responsible for administering
       the domain's zone file. Note that a "." is used instead of an "@" in the e-mail

    3. Serial number - The revision number of this zone file.

    4. Refresh Time - The time, in seconds, a secondary DNS server waits before
       querying the primary DNS server's SOA record to check for changes.

    5. Retry time - The time, in seconds, a secondary server waits before retrying a
       failed zone transfer

    6. Expire time - The time, in seconds, that a secondary server will keep trying to
       complete a zone transfer

    7. Minimum TTL - The minimum time-to-live value applies to all resource records
       in the zone file.

Amal200221480, Buthaina 200224233, Latifa 200221763, Maryam. S 200221977                     HD2

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