DNS
From Proprofs
You are here: Home > Schools > Comptia > Network+ Certification > Wiki Home >Study Guide
Contents |
[edit section] DNS
DNS (Domain Name System) is the name resolution protocol of choice in the TCP/IP suite. It is responsible for name resolution as it is commonly known; for example, most people know the website “ProProfs” as www.ProProfs.com, as opposed to its logical identity, 208.43.76.251. Name resolution is essentially a service that allows for a more user-friendly experience and eliminates or at least reduces the need of a user to memorize physical or logical addresses. The name resolution offered by DNS is provided by DNS name servers, meaning that DNS operates in a client-server access method. The Network+ exam will test you on your ability to differentiate between several types of name servers, domain names, and of course, name server records. Typically, the exam will have at least three questions on or related to DNS name resolution.
[edit section] Name Servers
DNS name servers are responsible for handling requests to translate user-friendly “domain names” into logical IP addresses. Typically, a one-to-one correlation exists between a domain name and the IP address it maps to. However, the reverse is not always the case: many domain names can point to a single IP address. The name resolution entries (DNS entries) are stored in a file on the DNS name server, so requests to a server typically involve the server checking its DNS entries for the name; if the name server does not have an entry for that name, it may try to forward the request to other DNS servers (hence, the Internet). If it is determined that no entry exists for that name, the DNS server will return an error to the requesting client. Name servers are typically differentiated as either primary or secondary:
- Primary name servers handle client requests, checking a request against the DNS entries stored in a local file.
- Secondary name servers provide redundancy and can allow for additional checking of DNS entries. Typically, a primary server that is bogged down might forward the request to a secondary name server.
[edit section] Hierarchy
Not all domain names are created equal. In fact, you’ve probably noticed before that domain names can be very long, like accounting.administration.company.com. Or, account names can be very short, like yahoo.com or proprofs.com. Many websites use the style www.subdomain.com, but they are certainly not restricted to this form of naming (the “www.*” convention in particular).
Internet DNS names can be broken down into two basic categories: TLD, or Top Level Domains, and all the others, or subdomains. TLD include such favorites as .com, .us, and .info, while sub-domains include such common entries as www.yahoo.com and uncommon ones, like city.county.state.country.gov. In general, TLD are the final suffix of any domain, whereas subdomains are domains that fall under a TLD.
[edit section] DNS Records
At the core of the DNS experience are the DNS records, the data that is looked up by the name servers to return information to requesting DNS clients. Different types of records hold different types of information. Below is a short list of the records that you will be expected to know for the Network+ examination.
- Address (A) Record – This is by far the most important DNS record as it maps a given domain name (DNS name) into an IP address. Note this is a one-to-one function.
- Pointer (PTR) Record – The opposite of the A record; translates IP addresses into DNS names
- Name Server (NS) Record – Identifies the DNS server that has authority over a particular domain
- Mail Exchange (MX) Record – Identifies the mail server that has authority for a particular domain
- Canonical Name (CNAME) Record – Used to map a subdomain (or another domain entirely) to a domain. In other words, it is used to “alias” a domain. For example, most websites have a CNAME Record that maps www.website.com to website.com
[edit section] Quick Review
1. A customer complains that his website (www.customerfirst.com) is not working properly. He says, “I can visit the website customerfirst.com, but when I type www.customerfirst.com, I get an error message.” Which of the following is most likely to be the record that he needs to fix or add?
a. Name server is incorrect
b. TCP/IP issue
c. A Record
d. NS Record
e. CNAME Record
2. Which of the following is a TLD?
a. Top.level.domain.com
b. Domain.com
c. www.domain.com
d. .com
e. proprofs.com
f. All of the above
[edit section] Answers
1. Because the alias www.* is not working, it is likely to be a CNAME issue. The answer is E.
2. Only .com is a TLD. The answer is D.
Top 5 Contributors to this article
|
|||||||||||||
|