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      DHCP Questions

      What Is DHCP?

      Dynamic Host Configuration Protocol (DHCP) is a network protocol that enables a server to automatically assign an IP address to a computer from a defined range of numbers (i.e., a scope) configured for a given network

      What Is DORA In DHCP?

      DORA – Discover, Offer , Request , Acknowledgement.

      What Is The DHCP Process For Client Machine?

      1. A user turns on a computer with a DHCP client.
      2. The client computer sends a broadcast request (called a DISCOVER or DHCPDISCOVER), looking for a DHCP server to answer.
      3. The router directs the DISCOVER packet to the correct DHCP server.
      4. The server receives the DISCOVER packet. Based on availability and usage policies set on the server, the server determines an appropriate address (if any) to give to the client. The server then temporarily reserves that address for the client and sends back to the client an OFFER (or DHCPOFFER) packet, with that address information. The server also configures the client’s DNS servers, WINS servers, NTP servers, and sometimes other services as well.
      5. The client sends a REQUEST (or DHCPREQUEST) packet, letting the server know that it intends to use the address.
      6. The server sends an ACK (or DHCPACK) packet, confirming that the client has a been given a lease on the address for a server-specified period of time.

      What Protocol and Ports Are Used By DHCP And The DHCP Clients?

      DHCP, like BOOTP runs over UDP, utilizing ports 67 and 68. Requests are on UDP port 68, Server replies on UDP 67.

      DNS Questions

      Can you name the different DNS record types and their purpose?

      • a-record = forward lookup, name to IP address
      • ptr-record = reverse lookup, IP address to name
      • cname = fqdn to different fqdn

      How would you validate reverse record is working?

      • dig -x 1.2.3.4
      • nslookup -type=ptr 1.2.3.4

      What is the “in-addr.arpa” zone used for?

      • In a Domain Name System (DNS) environment, it is common for a user or an application to request a Reverse Lookup of a host name, given the IP address. This article explains this process. The following is quoted from RFC 1035: “The Internet uses a special domain to support gateway location and Internet address to host mapping. Other classes may employ a similar strategy in other domains. The intent of this domain is to provide a guaranteed method to perform host address to host name mapping, and to facilitate queries to locate all gateways on a particular network on the Internet.
        “The domain begins at IN-ADDR.ARPA and has a substructure which follows the Internet addressing structure. “Domain names in the IN-ADDR.ARPA domain are defined to have up to four labels in addition to the IN-ADDR.ARPA suffix. Each label represents one octet of an Internet address, and is expressed as a character string for a decimal value in the range 0-255 (with leading zeros omitted except in the case of a zero octet which is represented by a single zero).
        “Host addresses are represented by domain names that have all four labels specified.” Reverse Lookup files use the structure specified in RFC 1035.
        For example, if you have a network which is 150.10.0.0, then the Reverse Lookup file for this network would be 10.150.IN-ADDR.ARPA. Any hosts with IP addresses in the 150.10.0.0 network will have a PTR (or ‘Pointer’) entry in 10.150.IN- ADDR.ARPA referencing the host name for that IP address. A single IN- ADDR.ARPA file may contain entries for hosts in many domains. Consider the following scenario. There is a Reverse Lookup file 10.150.IN-ADDR.ARPA with the following contents: Exp : 1.20 IN PTR WS1.ACME.COM.

      What is forwarder?

      • When one DNS server can’t receive the query it can be forwarded to another DNS once configured as forwarder.

      Can you name the diff. types of DNS Queries?

      Recursion

      • In a recursive query, a DNS client provides a hostname, and the DNS Resolver “must” provide an answer—it responds with either a relevant resource record, or an error message if it can’t be found. The resolver starts a recursive query process, starting from the DNS Root Server, until it finds the Authoritative Name Server (for more on Authoritative Name Servers see DNS Server Types below) that holds the IP address and other information for the requested hostname.

      Iteration

      • In an iterative query, a DNS client provides a hostname, and the DNS Resolver returns the best answer it can. If the DNS resolver has the relevant DNS records in its cache, it returns them. If not, it refers the DNS client to the Root Server, or another Authoritative Name Server which is nearest to the required DNS zone. The DNS client must then repeat the query directly against the DNS server it was referred to.

      Non-Recursive Query

      • A non-recursive query is a query in which the DNS Resolver already knows the answer. It either immediately returns a DNS record because it already stores it in local cache, or queries a DNS Name Server which is authoritative for the record, meaning it definitely holds the correct IP for that hostname. In both cases, there is no need for additional rounds of queries (like in recursive or iterative queries). Rather, a response is immediately returned to the client.

      What are SRV records?

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

      What is the main purpose of SRV records ?

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

      What are the types of SRV records?

      • 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.

      What is primary, Secondary, stub & AD Integrated Zone?

      • Primary Zone: – zone which is saved as normal text file with filename (.dns) in DBS folder. Maintains a read, write copy of zone database.
      • Secondary Zone: – maintains a read only copy of zone database on another DNS server. Provides fault tolerance and load balancing by acting as backup server to primary server.
      • Stub zone: – contains a copy of name server and SOA records used for reducing the DNS search orders. Provides fault tolerance and load balancing.

      What are the benefits and scenarios of using Stub zones?

      Understanding stub zones

      • A stub zone is a copy of a zone that contains only those resource records necessary to identify the authoritative Domain Name System (DNS) servers for that zone.
      • A stub zone is used to resolve names between separate DNS namespaces. This type of resolution may be necessary when a corporate merger requires that the DNS servers for two separate DNS namespaces resolve names for clients in both namespaces.
        A stub zone consists of:
      • 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. The master servers for a stub zone are one or more DNS servers authoritative for the child zone, usually the DNS server hosting the primary zone for the delegated domain name.
        Use stub zones to:
      • Keep delegated zone information current.
      • By updating a stub zone for one of its child zones regularly, the DNS server hosting both the parent zone and the stub zone will maintain a current list of authoritative DNS servers for the child zone.
      • Improve name resolution.
      • Stub zones enable a DNS server to perform recursion using the stub zone’s list of name servers without needing to query the Internet or internal root server for the DNS namespace.
      • Simplify DNS administration.
      • By using stub zones throughout your DNS infrastructure, you can distribute a list of the authoritative DNS servers for a zone without using secondary zones. However, stub zones do not serve the same purpose as secondary zones and are not an alternative when considering redundancy and load sharing.
      • There are two lists of DNS servers involved in the loading and maintenance of a stub zone:
      • The list of master servers from which the DNS server loads and updates a stub zone. A master server may be a primary or secondary DNS server for the zone. In both cases, it will have a complete list of the DNS servers for the zone.
      • The list of the authoritative DNS servers for a zone. This list is contained in the stub zone using name server (NS) resource records. When a DNS server loads a stub zone, such as widgets.example.com, it queries the master servers, which can be in different locations, for the necessary resource records of the authoritative servers for the zone widgets.example.com. The list of master servers may contain a single server or multiple servers and can be changed anytime.

      What are the benefits and scenarios of using Conditional Forwarding?

      • Rather than having a DNS server forward all queries it cannot resolve to forwarders, the DNS server can forward queries for different domain names to different DNS servers according to the specific domain names that are contained in the queries. Forwarding according to these domain-name conditions improves conventional forwarding by adding a second condition to the forwarding process.
      • A conditional forwarder setting consists of a domain name and the IP address of one or more DNS servers. To configure a DNS server for conditional forwarding, a list of domain names is set up on the Windows Server 2003-based DNS server along with the DNS server IP address. When a DNS client or server performs a query operation against a Windows Server 2003- based DNS server that is configured for forwarding, the DNS server looks to see if the query can be resolved by using its own zone data or the zone data that is stored in its cache, and then, if the DNS server is configured to forward for the domain name that is designated in the query (a match), the query is forwarded to the IP address of a DNS Server that is associated with the domain name. If the DNS server has no domain name listed for the name that is designated in the query, it attempts to resolve the query by using standard recursion.

      We like to develop SME’s in multiple fields. If you could sum up your expertise in two primary points, what would those be?

      What motivates you on the job?

      We seek to hire problem solvers. When were you able to resolve a workplace relate problem?

      Tell me something about yourself that I wouldn’t know from reading your resume.

      Working for this company can become stressful from time to time. How do you handle stress on the job?

      What is your greatest weakness?

      What makes you a great problem solver?

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