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| Questão | Responda |
| What does DNS stand for ? | Domain Name Service |
| What is DNS | DNS is a hierarchical naming structure used to identify computers, services or resources |
| Why do we use DNS 2 reasons ? | *They're easier to read *They're easy to remember |
| What are labels in a domain name | Two or more parts called labels, that are separated by dots |
| Do different labels represent different level in hierarchy | Yes |
| What does FQDN mean and what is it ? | Fully Qualified Domain Name and it's the full domain name |
| What does TLD mean and what is it and give an example ? | Top Level Domain and its the last label in a domain name i.e .uk |
| What is a domain namespace | It's the hierarchal status of the root domain and the following TLD's |
| What is the root domain and is it visible | It's at the top of the DNS namespace and it's at the end of every domain name and it isn't visible but it is there |
| Name 3 TLD's | .com .uk .edu .gov |
| Are TLD's directly below the root ? Who controls them ? | Yes they are and they're controlled by the IANA (Internet Assigned Number Authority) |
| Who are TLD's managed by ? Do they assign domain name registrars ? | TLD Registry and Yes they do |
| Why is it important we have a TLD Registry ? | To prevent duplicate Domain names and already domain names from being taken |
| What is the whois protocol | It allows the registry to get info from the registrars about information regarding who can use what is gathered. |
| What is the DNS namespace cut up into | zones |
| What is a zone | A zone is a logical portion of the DNS namespace |
| What is each DNS zone looked after | Authoritative nameservers |
| What does a nameserver store ? | Resource records for the zone |
| Can a DNS name server be responsible for more than one zone ? | Yes |
| What is a more responsible way of managing a nameserver | By delegating a part of a zone to another nameserver which creates a sub-domain. An example of this having a DNS server for the uk zone and delegate responsibility to another DNS Server to look after the ac part of a zone. |
| What is Anycasting ? | Having the same IP Prefix in different locations to provide a decentralised service |
| What is clustering | Joining different servers together to provide a fault tolerance. If one cluster does go down the remaining servers are still able to provide a service |
| Where do DNS servers store the name for a domain | In a zone file |
| Are IP Addresses converted into domain names? | Yes |
| How does DNS work from a client perspective in this example | The client (PC) will ask the DNS server the IP Address for vle.salford.ac.uk. The DNS server will return this since it's the salford DNS server and the client can then connect to the site |
| In the previous example why is the client the resolver ? | It's the resolver because its asking the DNS Server the IP Address for a certain site |
| How does DNS work from a client perspective in this example | 1 - The client (PC) will ask the salford DNS server for the IP Address of the google domain name 2 - The salford DNS server doesn't know this since it doesn't manage this zone so it will ask the root DNS for the .com IP Address of this DNS server 3. It will return this and then the salford DNS server will ask the .com server for the IP Address of the google.com server 4. It will return this and then the salford DNS server will ask the google.com server for the IP Address of the google.com domain name 5. The google.com server will return this to the salford.ac.uk DNS Server which will then return this to the client |
| In this example who the resolver and why ? | The DNS servers and because they figure out the IP Addresses |
| What a recursive query ? | It's when the DNS client requires that the DNS server respond to the client with either the requested resource record or an error message stating that the record or domain name does not exist. |
| What are the problems with the examples before and what method is used to resolve this | It can place a huge query burden on DNS servers closer to the top of the tree. To resolve this we can cache the IP Address which has a Time To Live TTL |
| What are the issues with TTL and how can this be resolved ? | If the TTL is still in-date changes made to the DNS Server and info will be stored even if its out of date or old. To solve this we can only set the TTL for like a week or less to make sure changes get updated |
| What do most resource records belong to | Internet or iN class |
| Name the 6 resource record types | A AAAA CNAME MX NS SOA |
| What is the resource record A | Associates an IPv4 with a host name |
| What is the resource record AAAA | Associates an IPv6 address with a host name |
| What is the resource record CNAME | Associates an alternative name (alias) with a host name |
| What is the resource record MX | Associates a domain name with a list of mail servers serving that domain |
| What is the resource record NS | Associates a domain name with the host name of a DNS server that resolves queries for that domain |
| What is the resource record SOA | Associates a domain name with the host name of the DNS server that holds the authoritative version of the records for that domain |
| What are primary and secondary servers used for ? | Primary servers are used to hold the master copy of the zone file and the secondary holds a copy of this zone file |
| Why is it important to have a primary and secondary server ? | To prevent fault tolerance |
| What is the primary server normally called and what does it hold | It's normally called the master since this holds the main files and it holds the zone files, resource records to add and update, properties such as TTL are defined |
| What is the secondary server normally called | Slave |
| What are Glue records used for ? | To prevent queries from being stuck. |
| What issues do Glue records prevent and how can they be fixed ? | It prevents a DNS server from not returning an IP Address by adding a A(host) RR for the DNS server to the zone file on the DNS server. This is called a GLUE record |
| What 5 things does a secondary server do | Serial number - Tells a secondary server if it has the latest copy of the zone file Refresh - Tells a secondary server how often it should check with the primary to see if the zone file has changed If a secondary server cannot contact its primary then: Update Retry - tells the secondary how long to wait before trying again to contact the primary server Expiry - tells the secondary for how long it can continue to resolve query requests when out of touch with its primary Minimum - The default time for which returned records should be cached by resolvers |
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