Notable Replies

  1. Hi Raul,

    DNS supports both UDP and TCP but we typically only use TCP for zone transfers.

    One of the advantages of UDP is that it’s faster since it’s connectionless. A DNS server doesn’t have to establish a TCP connection with each client that does a DNS request. With UDP, it just gets a DNS request, sends a response and it’s done.


  2. Hi INderpreet,

    DNS allows us to use zones. A zone stores information about the domain. When you register a domain name, you have to tell the register which DNS servers you want to use for your domain name.

    On the DNS server that is responsible for your domain (zone) you can create different records.

    Let me give you a short overview of the different records:

    • A: the A record is used to store the IP address of a name. For example, refers to "networklessons.com".
    • AAAA: this is the same as the A record but it's used for IPv6 addresses.
    • CNAME: the CNAME record is an alias for an A record. For example, I could use CNAME www.networklessons.com as an alias for networklessons.com.
    • MX: the MX record is used to store the hostname for the mailserver. For example, I could use this to tell that mail.networklessons.com is the mail server for this domain name. You will need an A record for mail.networklessons.com.


  3. Hi Shawn O,

    In case your PC doesn’t have the MAC address of the gateway IP (which is the internal interface of the router) inside its ARP table, then It will issue an ARP request. With the ARP request, it will receive the MAC address from the router so it can start sending the packet. You can check this on the PC by going to the command line and typing the command “arp -a”

    Then the packet will go to the router who in turn send it to the ISP DNS Server for the IP to domain name mapping. Once the IP of google.com is known, then the route of the packet happens to reach the web Server of google.

    Hope I could answer your question.

  4. Hi Maher,

    How does this PC know that the request to reach http://google.com needs to send to the ISP DNS server instead of the local DNS server?
    How does this PC know the IP address of the ISP DNS server?

    Whijoon Yim,

  5. Hi @whijoon

    On your computer, you have to configure the DNS server manually or you receive it through the DHCP server:

    You could configure the DNS server of your ISP or anything else ( is Google DNS).

    It’s also possible that you see the IP address of your local router here. Most SOHO routers will act as a “proxy” / simple DNS server for your computers. When it receives a DNS request, it will forward it to the ISP DNS servers to figure out the IP address that belongs to the hostname. This is then returned to the computer.

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