DNS: Domain Name System

Nameservers, record types. Links: step-by-step video on domain resolution, faq about root nameservers

18 flashcards · Computer Science · by lakesare

1. What's a naked domain?

   Domain name without the "www" or any other subdomains.

2. What's a domain registrar?

   A domain registrar offers services that allow you to pick a domain name and register it to an IP address.

3. What's usually meant by a web host?

   Website hosting provides server storage space and an IP address for your website.

4. What is a root nameserver?

   One of 13 nameservers, that gets e.g. www.memcode.com and returns an IP address.

5. Why are there only 13 root nameservers?

   The number 13 is based on a constraint of Internet Protocol (IP) version 4 (IPv4). Root nameservers are a network of hundreds of servers in countries around the world. However, together they are identified as 13 named servers.

6. What is nameserver?

   Any server capable of providing you with an IP:domain_name mapping, - either a recursive or authoritative nameserver.

7. Forward VS reverse DNS lookups?

   forward: memcode.com --> 23.23.73.154 reverse: 23.23.73.154 --> memcode.com

8. How are 13 root nameservers named?

   a.root-servers.net ... m.root-servers.net Starting with ‘A’ and extending to the letter ‘M’. (Note that these systems belong to the root-servers.net Internet domain, making their fully-qualified names like "a.root-servers.net," for example.)

9. What is DNS hijacking?

   Practice of subverting a resolution of DNS queries. You do a forward lookup of memcode.com, but get 66.66.66.666 ip in return.

10. Name 2 reasons for DNS hijacking. How to go around it?

    malware that overrides laptop's TCP/IP configurations, and directs you to a fake site. your ISP provider, e.g. to block some resource out of censorship. Google in April 2016 launched DNS-over-HTTPS service. This scheme can overcome the limitations of the legacy DNS protocol. It performs remote DNSSEC check and transfers the results in a secure HTTPS tunnel.

11. What are the TLDs here?

    Top Level Domains: com, edu, uk, etc. Children of the . (root).

12. Name some fully qualified domain name from here:

    www.bbc.co.uk. Usually browser inserts the root (.) automatically, so we don't need to worry about that.

13. What is shown here?

    DNS zones. Eg, eng must only know IPs of dev and testing, and it can delegate resolving of a domain to dev. Each domain name server is divided into zones. A single server may only be responsible for knowing the host names and IP addresses for a small subset of a zone, but DNS servers can work together to map all domain names to their IP addresses. That means if one domain name server is unable to find the IP addresses of a requested domain then it requests the information from other domain name…

14. What's an authoritative nameserver? Give example.

    Nameserver that can answer with either: authoritative data from its own db, a referral (e.g. "I don't know that answer, but you can talk to server so-and-so, who answers questions for this subdomain..). (in contrast to answers obtained via a query to another name server that only maintains a cache of data) Authoritative nameservers: 13 root servers, .com zone nameserver. Not authoritative nameservers: your ISP nameserver.

15. What usually happens when your computer tries to perform a forward DNS lookup?

    www.memcode.com Your computer has an IP of your ISP recorded somewhere, and. It ask ISP's nameserver to do a lookup for us. ISP's nameserver goes to one of 13 root nameservers. Any of the 13 root servers know all the TLDs. They tell us an IP of .com authoritative nameserver. .com authoritative nameserver tells us an IP of memcode. ISP's nameserver gets the result, and returns it to us.

16. A vs CNAME DNS record types?

    A (for IP4) or AAAA (for IP6) - maps domain to IP. CNAME - maps domain to another domain. A stands for Address, CNAME stands for Canonical Name.

17. What's a synthetic record?

    Automatically-generated collection of DNS records related to a specific feature. This allows you to add common features, such as blog.memcode.com, to your domain in one step.

18. Name 2 types of DNS queries.

    recursive: client queries a nameserver, which will then continue querying on client's behalf iterative: client queries authoritative nameservers one by one, following their referrals