DNS Help

alliasneoalliasneo Member Posts: 186
Hi, I was just wondering if someone can help me out with the DNS process. I'm not sure how much I'm supposed to know for the CCENT exam.

My understanding so far.

A DNS server can be local or remote.
A computer requests a webpage or pings a PC by name - a DNS packet will be generated and directed to the DNS server?
The DNS server will respond with the IP address of the PC name and the Host can then get the webpage/ping the comptuter.

I'm sure there is more to it than this but this I what I understand at the moment. Where do MAC addresses come in to this? They just act locally right so if the server is remote the PC with arp to the default-gateway? and if the server is local the host will arp for the DNS IP address?



  • dead_p00ldead_p00l Member Posts: 136
    This is a pretty decent and simple explanation. Hope it helps.

    HowStuffWorks "How Domain Name Servers Work"
    This is our world now... the world of the electron and the switch, the
    beauty of the baud.
  • BrakarificBrakarific Member Posts: 23 ■□□□□□□□□□
    MAC addresses are generally important to the local link only. They aren't passed on from hop to hop at Layer 3, that being said, L2 switches do maintain a MAC address table that sometimes has MAC address info in them that aren't necessarily directly connected to the switch. For example, if your DNS server is on the same vlan as your pc, but is 3 or 4 switches away, your local switch will either know which port is associated with the DNS server MAC, or it will broadcast until it knows which port is the one to send to. That being said, if the DNS server is on a different VLAN or a different network, the DNS server MAC is of no importance to the PC and vice versa.
  • pham0329pham0329 Member Posts: 556
    The MAC address comes into play whenever you communicate over the network. As far as DNS, it's pretty in depth and you won't really need to know the entire process for the CCNA, but here's a quick overview of the steps
    • When the client ping google.com, the client first checks its dns cache to see if it already has a record for google.com. If not, it'll send a query to the DNS server
    • When the server receives it, it checks to see if it has a zone for google.com. If not, it checks to see if there's a record in its cache. If not, then it sends a recursive query to the forwarding dns, or the root dns servers.
    • If a forwarding dns is configured, the forwarding dns goes through the same process, and if it doesn't know the answer, it forwards the request to the Root DNS servers.
    • The root dns server receives the request for Google, and it'll reply back with the IP for the .com dns server
    • The .com dns server receives the request and reply back with the IP for google.com dns server
    • The google.com dns gets the request, and replies back with the IP of www
    • Your dns server gets the reply back, and add it to its cache and send you the result. You add it to your cache.
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