DNS Interview Questions and Answers

DNS Interview Questions and Answers

DNS Interview Questions and Answers

Here are all server dns Interview Questions and Answers & active directory interview questions

Q1. What is the main purpose of a DNS server?

Ans: DNS servers are used to resolve FQDN hostnames into IP addresses and vice versa.

Q2. What is the port no of dns ?

Ans: 53.

Q3. What is a Forward Lookup?

Ans: Resolving Host Names to IP Addresses.

Q4. What is Reverse Lookup?

Ans: It?s a file contains host names to IP mapping information.

Q5. What is a Resource Record?

Ans: It is a record provides the information about the resources available in the N/W infrastructure.

Q6. What are the diff. DNS Roles?

Ans: Standard Primary, Standard Secondary, & AD Integrated.

Q7. What is a Zone?

Ans: Zone is a sub tree of DNS database.

Q8. What is DNS?

Ans: Domain Name System is a service that can be installed on any windows server operating system to resolve the Name to IPAddress and vice-versa. TCP/IP networks, such as the Internet, use DNS to locate computers and services through user-friendly names

Q9. What is DDNS?

Ans: Dynamic DNS or DDNS is a method of updating, in real time, a Domain Name System to point to a changing IP address on the Internet. This is used to provide a persistent domain name for a resource that may change location on the network.

Q10. What are the resource records in DNS?

Ans:

  • A (Address) Maps a host name to an IP address. When a computer has multiple adapter cards and IP addresses, it should have multiple address records.
  • CNAME (Canonical Name) Sets an alias for a host name. For example, using this record, zeta.tvpress.com can have an alias as www.tvpress.com.
  • MX (Mail Exchange) Specifies a mail exchange server for the domain, which allows mail to be delivered to the correct mail servers in the domain.
  • NS (Name Server) Specifies a name server for the domain, which allows DNS lookups within various zones. Each primary and secondary name server should bedeclared through this record.
  • PTR (Pointer) Creates a pointer that maps an IP address to a host name for reverse lookups.
  • SOA (Start of Authority) Declares the host that is the most authoritative for the zone and, as such, is the best source of DNS information for the zone. Each zone file must have an SOA record (which is created automatically when you add a zone).

Q11. How do you manually create SRV records in DNS?

Ans: This is on windows server go to run —> dnsmgmt.msc rightclick on the zone you want to add srv record to and choose “other new record” and choose service location(srv).

Q12. What is the main purpose of SRV records ?

Ans: SRV records are used in locating hosts that provide certain network services.

Q13. Before installing your first domain controller in the network, you installed a DNS server and created a zone, naming it as you would name your AD domain. However, after the installation of the domain controller, you are unable to locate infrastructure SRV records anywhere in the zone. What is the most likely cause of this failure ?

Ans: The zone you created was not configured to allow dynamic updates. The local interface on the DNS server was not configured to allow dynamic updates.

Q14. Which of the following conditions must be satisfied to configure dynamic DNS updates for legacy clients ?

Ans: The zone to be used for dynamic updates must be configured to allow dynamic updates. The DHCP server must support, and be configured to allow, dynamic updates for legacy clients.

 Q15. At some point during the name resolution process, the requesting party received authoritative reply. Which further actions are likely to be taken after this reply ?

Ans: After receiving the authoritative reply, the resolution process is effectively over.

Q16. What are a Forward and Reverse Lookup?

Ans:

  • Forward Lookup: When a name query is send to the DNS server against to IP address, it is generally said a forward lookup.
  • Reverse Lookup: DNS also provides a reverse lookup process, enabling clients to use a known IP address during a name query and look up a computer name based on its address.

Q17. What is Primary zone?

Ans: This is the read and writable copy of a zone file in the DNS namespace. This is primary source for information about the zone and it stores the master copy of zone data in a local file or in AD DS. Dy default the primary zone file is named as zone_name.dns in %windir%System32DNS folder on the server.

Q18. What id Secondary zone?

Ans: This is the read only copy of a zone file in the DNS namespace. This is secondary source for information about the zone and it get the updated information from the master copy of primary zone. The network access must be available to connect with primary server. As secondary zone is merely a copy of a primary zone that is hosted on another server, it cannot be stored in AD DS.

Q19. What is stub Zone?

Ans: A stub zone is a read only copy of a zone that contains only those resource records which are necessary to identify the authoritative DNS servers for that particular zone. A stub zone is practically used to resolve names between separate DNS namespaces. This type of zone is generally created when a corporate merger or acquire and DNS servers for two separate DNS namespaces resolve names for clients in both namespaces.

A stub zone contains:

The start of authority (SOA) resource record, name server (NS) resource records, and the glue A resource records for the delegated zone.

The IP address of one or more master servers that can be used to update the stub zone.

Secure services in your network require reverse name resolution to make it more difficult to launch successful attacks against the services. To set this up, you configure a reverse lookup zone and proceed to add records. Which record types do you need to create?

Q20. SOA records must be included in every zone. What are they used for ?

Ans: SOA records contain a TTL value, used by default in all resource records in the zone. SOA records contain the e-mail address of the person who is responsible for maintaining the zone. SOA records contain the current serial number of the zone, which is used in zone transfers.

Q21. By default, if the name is not found in the cache or local hosts file, what is the first step the client takes to resolve the FQDN name into an IP address ?

Ans: Performs a recursive search through the primary DNS server based on the network interface configuration .

Q22. What is Caching Only Server?

Ans: Caching-only servers are those DNS servers that only perform name resolution queries, cache the answers, and return the results to the client. Once the query is stored in cache, next time the query in resolved locally from cached instead of going to the actual site.

Q23. What is Aging and Scavenging?

Ans: DNS servers running Windows Server support aging and scavenging features. These features are provided as a mechanism to perform cleanup and removal of stale resource records from the server and zone. This feature removes the dynamically created records when they are stamped as stale.

By default, the aging and scavenging mechanism for the DNS Server service is disabled.

Scavenging and aging must be enabled both at the DNS server and on the zone

Q24. What is SRV record in DNS?

Ans: The SRV record is a resource record in DNS that is used to identify or point to a computer that host specific services i.e Active directory.

Q25. What is Forwarding in DNS?

Ans: A forwarder is a feature in DNS server that is used to forward DNS queries for external DNS names to DNS servers outside of that network. We ca configure a DNS server as a forwarder to forward the name query to other DNS servers in the network when they cannot resolve locally to that DNS server.

Q26. What is Conditional Forwarding in DNS?

Ans: We can configure the DNS server to forward queries according to specific domain names using conditional forwarders. In this case query is forward to an IP address against a DNS domain name.

Q27. What does a zone consist of & why do we require a zone?

Ans: Zone consists of resource records and we require zone for representing sites.

Q28. What is Caching Only Server?

Ans: When we install 2000 & 2003 server it is configured as caching only server where it maintains the frequently accessed sites information and again when we access the same site for next time it is obtain from cached information instead of going to the actual site.

Q29. What is forwarder?

Ans: When one DNS server can?t receive the query it can be forwarded to another DNS once configured as forwarder.

Dns interview questions

Q30. What is secondary DNS Server?

Ans: It is backup for primary DNS where it maintains a read only copy of DNS database.

Q31. How to enable Dynamic updates in DNS?

Ans: Start>Program>Admin tools> DNS >Zone properties.

Q32. What are the properties of DNS server?

Ans: INTERFACES, FORWARDERS, ADVANCED, ROUTINGS, SECURITY, MONITORING, LOGGING, DEBUG LOGGING.

Q33. Properties of a Zone ?

Ans: General, SOA, NAMESERVER, WINS, Security, and ZONE Transfer.

Q34. What is scavenging?

Ans: Finding and deleting unwanted records.

Q35. What are SRV records?

Ans: SRV are the service records, there are 6 service records. They are useful for locating the services.

Q36. What are the types of SRV records?

Ans: MSDCS:Contains DCs information.

TCP:Contains Global Catalog, Kerberos & LDAP information.

UDP:Contains Sites information.

Sites:Contains Sites information.

Domain DNS Zone:Conations domain?s DNS specific information.

Forest DNS zone:Contains Forest?s Specific Information.

Q37. Where does a Host File Reside?

Ans: c:\windows\system32\drivers\etc.

Q38. What is SOA?

Ans: Start of Authority: useful when a zone starts. Provides the zone startup information.

Q39. What is a query?

Ans: A request made by the DNS client to provide the name server information.

Q40. What are the diff. types of Queries?

Ans: Recursion, iteration.

Q41. Tools for troubleshooting DNS?

Ans: DNS Console, NSLOOKUP, DNSCMD, IPCONFIG, Logs.

Q42. What is WINS server? where we use WINS server? difference between DNS and WINS?

Ans: WINS is windows internet name service used to resolve the NetBIOS(computer name)name to IP address.This is proprietary for Windows.You can use in LAN.DNS is a Domain Naming System, which resolves Host names to IP addresses. It uses fully qualified domain names. DNS is an Internet standard used to resolve host names.

Q42. What is new in Windows Server 2003 regarding the DNS management?

Ans: When DC promotion occurs with an existing forest, the Active Directory Installation Wizard contacts an existing DC to update the directory and replicate from the DC the required portions of the directory.

If the wizard fails to locate a DC, it performs debugging and reports what caused the failure and how to fix the problem. In order to be located on a network, every DC must register in DNS DC locator DNS records. The Active Directory Installation Wizard verifies a proper configuration of the DNS infrastructure. All DNS configuration debugging and reporting activity is done with the Active Directory Installation Wizard.

Q43. SOA records must be included in every zone. What are they used for?

Ans: SOA records contain a TTL value, used by default in all resource records in the zone. SOA records contain the e-mail address of the person who is responsible for maintaining the zone. SOA records contain the current serial number of the zone, which is used in zone transfers.

By default, if the name is not found in the cache or local hosts file, what is the first step the client takes to resolve the FQDN name into an IP address? Performs a recursive search through the primary DNS server based on the network interface configuration.

Q44. How do I clear the DNS cache on the DNS server?

Ans: Go to cmd prompt and type ipconfig /flushdns .

Q45. What is the main purpose of SRV records?

Ans: SRV records are used in locating hosts that provide certain network services.

Q46. Before installing your first domain controller in the network, you installed a DNS server and created a zone, naming it as you would name your AD domain. However, after the installation of the domain controller, you are unable to locate infrastructure SRV records anywhere in the zone. What is the most likely cause of this failure?

Ans: The zone you created was not configured to allow dynamic updates. The local interface on the DNS server was not configured to allow dynamic updates.

Q47. What is the “.” zone in my forward lookup zone?

Ans: This setting designates the Windows 2000 or Windows Server 2003 DNS server to be a root hint server and is usually deleted. If you do not delete this setting, you may not be able to perform external name resolution to the root hint servers on the Internet.

Q48. Do I need to configure forwarders in DNS?

Ans: No. By default, Windows 2000 DNS uses the root hint servers on the Internet; however, you can configure forwarders to send DNS queries directly to your ISP’s DNS server or other DNS servers. Most of the time, when you configure forwarders, DNS performance and efficiency increases, but this configuration can also introduce a point of failure if the forwarding DNS server is experiencing problems.

The root hint server can provide a level of redundancy in exchange for slightly increased DNS traffic on your Internet connection. Windows Server 2003 DNS will query root hints servers if it cannot query the forwarders.

Q49. Should I point the other Windows 2000-based and Windows Server 2003-based computers on my LAN to my ISP’s DNS servers?

Ans: No. If a Windows 2000-based or Windows Server 2003-based server or workstation does not find the domain controller in DNS, you may experience issues joining the domain or logging on to the domain. A Windows 2000-based or Windows Server 2003-based computer’s preferred DNS setting should point to the Windows 2000 or Windows Server 2003 domain controller running DNS.

If you are using DHCP, make sure that you view scope option #15 for the correct DNS server settings for your LAN.

Q50. Do I need to point computers that are running Windows NT 4.0 or Microsoft Windows 95, Microsoft Windows 98, or Microsoft Windows 98 Second Edition to the Windows 2000 or Windows Server 2003 DNS server?

Ans: Legacy operating systems continue to use NetBIOS for name resolution to find a domain controller; however it is recommended that you point all computers to the Windows 2000 or Windows Server 2003 DNS server for name resolution.

Q51. What if my Windows 2000 or Windows Server 2003 DNS server is behind a proxy server or firewall?

Ans: If you are able to query the ISP’s DNS servers from behind the proxy server or firewall, Windows 2000 and Windows Server 2003 DNS server is able to query the root hint servers. UDP and TCP Port 53 should be open on the proxy server or firewall.

Q52. What should I do if the domain controller points to itself for DNS, but the SRV records still do not appear in the zone?

Ans: Check for a disjointed namespace, and then run Netdiag.exe /fix.

You must install Support Tools from the Windows 2000 Server or Windows Server 2003 CD-ROM to run Netdiag.exe.

Q53. How do I set up DNS for a child domain?

Ans: To set up DNS for a child domain, create a delegation record on the parent DNS server for the child DNS server. Create a secondary zone on the child DNS server that transfers the parent zone from the parent DNS server.

Note Windows Server 2003 has additional types of zones, such as Stub Zones and forest-level integrated Active Directory zones, that may be a better fit for your environment. Set the child domain controller to point to itself first. As soon as an additional domain controller is available, set the child domain controller to point to this domain controller in the child domain as its secondary.

Q54. What are Queries types in DNS?

Ans:

  • Recursive Query: This name queries are generally made by a DNS client to a DNS server or by a DNS server that is configured to pass unresolved name queries to another DNS server, in the case of a DNS server configured to use a forwarder.
  • Iterative Query: An iterative name query is one in which a DNS client allows the DNS server to return the best answer it can give based on its cache or zone data. If the queried DNS server does not have an exact match for the queried name, the best possible information it can return is a referral. The DNS client can then query the DNS server for which it obtained a referral. It continues this process until it locates a DNS server that is authoritative for the queried name, or until an error or time-out condition is met.

Q55. What are Tools for troubleshooting of DNS?

Ans: DNS Console, NSLOOKUP, DNSCMD, IPCONFIG, DNS Logs.

Q56. How to check DNS health?

Ans: Using the DCdiag.

i.e. (dcdiag /test:dns /v /e)

……Best Of Luck…..

 

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