w5ch3
159 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is an FQDN in the context of Domain Name System?

  • A domain name that contains partial labels of a host
  • A domain name that contains the full name of a host (correct)
  • A null label that defines the name of a host
  • A label that uniquely defines the name of a host

    • What is the purpose of the null label in an FQDN?

  • To uniquely identify the host
  • To define the end of the domain name
  • To define the start of the domain name
  • To indicate the end of the domain name with a dot (.) (correct)

    • What is a Partially Qualified Domain Name (PQDN)?

  • A domain name that contains no labels
  • A domain name that starts from a node but does not reach the root (correct)
  • A domain name that starts from the root
  • A domain name that contains all labels of a host

    • What is the purpose of the DNS client in resolving a PQDN?

    <p>To supply the missing part (suffix) to create an FQDN</p> Signup and view all the answers

    What is a domain in the context of Domain Name System?

    <p>A subtree of the domain name space</p> Signup and view all the answers

    Why is it inefficient to have just one computer store the domain name space?

    <p>Because it is very inefficient and also unreliable</p> Signup and view all the answers

    What is the process of dividing a domain into smaller domains called?

    <p>Subdomain creation</p> Signup and view all the answers

    What is the purpose of distributing the domain name space?

    <p>To make it more efficient and reliable</p> Signup and view all the answers

    What type of query is sent when a client wants to map an IP address to a domain name?

    <p>PTR query</p> Signup and view all the answers

    How is the IP address modified before sending a PTR query?

    <p>The IP address is reversed and in-addr and arpa labels are added</p> Signup and view all the answers

    What happens when a client asks for a recursive answer from a name server?

    <p>The server responds with the final answer</p> Signup and view all the answers

    What is the purpose of the inverse domain in DNS?

    <p>To map IP addresses to domain names</p> Signup and view all the answers

    What happens when a server is not the authority for a domain name in recursive resolution?

    <p>The server sends the query to another server</p> Signup and view all the answers

    What type of resolution occurs when a client does not ask for a recursive answer?

    <p>Iterative resolution</p> Signup and view all the answers

    What is the role of the client in iterative resolution?

    <p>The client is responsible for repeating the query to another server</p> Signup and view all the answers

    What is the purpose of the in-addr and arpa labels in a PTR query?

    <p>To make the IP address acceptable by the inverse domain</p> Signup and view all the answers

    What is the responsibility of an original server in a domain?

    <p>It has a zone, but the detailed information is kept by the lower-level servers.</p> Signup and view all the answers

    What is the purpose of a root server?

    <p>To delegate its authority to other servers, keeping references to those servers.</p> Signup and view all the answers

    What is the difference between a primary server and a secondary server?

    <p>A primary server updates zone files, while a secondary server does not.</p> Signup and view all the answers

    What is the purpose of a secondary server?

    <p>To create redundancy for the data so that if one server fails, the other can continue serving clients.</p> Signup and view all the answers

    What is the role of a primary server?

    <p>To create, maintain, and update the zone file.</p> Signup and view all the answers

    What happens if a primary server fails?

    <p>The secondary server continues serving clients.</p> Signup and view all the answers

    What is the relationship between a primary server and a secondary server?

    <p>A primary server and a secondary server are at the same level of authority.</p> Signup and view all the answers

    What is the role of a root server in the domain name space?

    <p>It covers the whole domain name space.</p> Signup and view all the answers

    What is the purpose of a question record in DNS?

    <p>To get information from a server</p> Signup and view all the answers

    What type of records are present in the answer section of a DNS response message?

    <p>Resource records</p> Signup and view all the answers

    What is the purpose of the authoritative section in a DNS response message?

    <p>To give information about one or more authoritative servers</p> Signup and view all the answers

    What is the role of a registrar in DNS?

    <p>To verify and add new domain names to the DNS database</p> Signup and view all the answers

    What is a resource record associated with in DNS?

    <p>Each node on the DNS tree</p> Signup and view all the answers

    What is the purpose of the additional information section in a DNS response message?

    <p>To provide additional information that may help the resolver</p> Signup and view all the answers

    What is returned by the DNS server to the client?

    <p>Resource records</p> Signup and view all the answers

    What is the purpose of ICANN in the context of DNS?

    <p>To accredit registrars</p> Signup and view all the answers

    What information does an organization need to provide to register?

    <p>Its server name and IP address</p> Signup and view all the answers

    What was the limitation of the initial DNS design?

    <p>It required manual updating for changes</p> Signup and view all the answers

    What is the main purpose of Dynamic Domain Name System (DDNS)?

    <p>To update DNS master files dynamically</p> Signup and view all the answers

    How do secondary servers get notified about changes in the zone in active notification?

    <p>The primary server sends a message to them</p> Signup and view all the answers

    What is the purpose of authentication in DDNS?

    <p>To provide security and prevent unauthorized changes</p> Signup and view all the answers

    What protocol is used by DNS when the size of the response message is less than 512 bytes?

    <p>UDP</p> Signup and view all the answers

    What is the well-known port used by the DNS server?

    <p>Port 53</p> Signup and view all the answers

    When is a TCP connection used in DNS?

    <p>When the size of the response message is more than 512 bytes</p> Signup and view all the answers

    What is the purpose of the generic domains in the domain name space?

    <p>To define registered hosts according to their generic behavior</p> Signup and view all the answers

    What type of query is sent when a server wants to map an IP address to a domain name?

    <p>Inverse query</p> Signup and view all the answers

    What is the name of the first-level node in the inverse domain?

    <p>arpa</p> Signup and view all the answers

    What is the purpose of the country domains section?

    <p>To use two-character country abbreviations</p> Signup and view all the answers

    What is the hierarchical structure of the inverse domain based on?

    <p>The netid part of the address being at a higher level than the subnetid part</p> Signup and view all the answers

    What is the purpose of the in-addr node in the inverse domain?

    <p>To be the second-level node in the inverse domain</p> Signup and view all the answers

    What is the relationship between the generic domains and the country domains?

    <p>They are separate sections of the domain name space</p> Signup and view all the answers

    What is the purpose of the domain name space?

    <p>To provide a hierarchical structure for organizing domain names</p> Signup and view all the answers

    What is the process of finding an IP address from a domain name or vice versa called?

    <p>Name-address resolution</p> Signup and view all the answers

    What type of application is DNS designed as?

    <p>Client-server</p> Signup and view all the answers

    What is the maximum number of levels in a domain name space?

    <p>128</p> Signup and view all the answers

    What is the role of a resolver in DNS?

    <p>To request domain name information</p> Signup and view all the answers

    What happens if a local DNS server cannot resolve a query?

    <p>All of the above</p> Signup and view all the answers

    What is the maximum length of a label in a domain name?

    <p>63 characters</p> Signup and view all the answers

    What is the format of an IP address in a PTR query?

    <p>Inverse order with 'in-addr.arpa' appended</p> Signup and view all the answers

    How are domain names read in a domain name space?

    <p>From the node up to the root</p> Signup and view all the answers

    What is the purpose of a central authority in a domain name space?

    <p>To assign the part of the domain name that defines the nature of the organization</p> Signup and view all the answers

    How is a domain name read in DNS?

    <p>From bottom to top</p> Signup and view all the answers

    What is the term for the process of a resolver receiving a response from a DNS server?

    <p>Interpretation</p> Signup and view all the answers

    What is the root label in a domain name space?

    <p>A null string</p> Signup and view all the answers

    What type of domain is 'chal.atc.jhda.edu.' an example of?

    <p>Generic domain</p> Signup and view all the answers

    What is the purpose of children having different labels in a domain name space?

    <p>To ensure the uniqueness of domain names</p> Signup and view all the answers

    What is the last character of a full domain name?

    <p>A dot</p> Signup and view all the answers

    What is a fully qualified domain name (FQDN) in the context of DNS?

    <p>A domain name that is terminated by a null string</p> Signup and view all the answers

    What is the main purpose of the identification subfield in DNS messages?

    <p>To match the response with the query</p> Signup and view all the answers

    Which section is present in both query and response messages in DNS?

    <p>Question section</p> Signup and view all the answers

    Which section of a DNS response message contains the answer from the server to the client?

    <p>Answer Section</p> Signup and view all the answers

    What is the total size of the header in DNS messages?

    <p>12 bytes</p> Signup and view all the answers

    What is the role of a registrar in DNS?

    <p>To add new domains to DNS</p> Signup and view all the answers

    What type of records are associated with each domain name (each node on the tree)?

    <p>Resource Records</p> Signup and view all the answers

    Which subfield contains the number of queries in the question section of the message?

    <p>Number of question records subfield</p> Signup and view all the answers

    What is the purpose of the authoritative section in a DNS response message?

    <p>To give information about one or more authoritative servers for the query</p> Signup and view all the answers

    What happens to mappings with an expired TTL in the cache memory?

    <p>They are purged periodically</p> Signup and view all the answers

    What is the purpose of the additional information section in a DNS response message?

    <p>To provide additional information that may help the resolver</p> Signup and view all the answers

    What is the purpose of the flags subfield in DNS messages?

    <p>To specify the type of answer requested</p> Signup and view all the answers

    What is the purpose of the question records in DNS messages?

    <p>To specify the question being asked</p> Signup and view all the answers

    What is the format of both query and response messages in DNS?

    <p>Same format for both query and response messages</p> Signup and view all the answers

    What is the purpose of a question record in DNS?

    <p>To get information from a server</p> Signup and view all the answers

    What is the role of ICANN in the context of DNS?

    <p>To accredit registrars</p> Signup and view all the answers

    What is the main disadvantage of a flat name space in the context of DNS?

    <p>It allows ambiguity and duplication</p> Signup and view all the answers

    What is the purpose of dividing the host file information into smaller parts in DNS?

    <p>To reduce the traffic on the Internet</p> Signup and view all the answers

    How are the names assigned to machines ensured to be unique in DNS?

    <p>By using a name space with complete control over the binding between the names and IP addresses</p> Signup and view all the answers

    What type of name space is used by the Domain Name System (DNS)?

    <p>Hierarchical name space</p> Signup and view all the answers

    What is the advantage of using a hierarchical name space in DNS?

    <p>It allows the authority to assign and control the name spaces to be decentralized</p> Signup and view all the answers

    What is the problem with storing the entire host file in a single computer?

    <p>It creates a huge amount of traffic on the Internet</p> Signup and view all the answers

    What is the role of the hierarchical name space in DNS?

    <p>To map each address to a unique name</p> Signup and view all the answers

    Why is decentralization of control important in DNS?

    <p>To allow the authority to assign and control the name spaces to be decentralized</p> Signup and view all the answers

    What is the primary purpose of the inverse domain in DNS?

    <p>To map an IP address to a domain name</p> Signup and view all the answers

    What is the first-level node in the inverse domain?

    <p>arpa</p> Signup and view all the answers

    What is the purpose of the country domains section?

    <p>To use two-character country abbreviations</p> Signup and view all the answers

    How is the hierarchical structure of the inverse domain organized?

    <p>By IP addresses, subnet IDs, and host IDs</p> Signup and view all the answers

    What is the purpose of the generic domains section?

    <p>To define registered hosts according to their generic behavior</p> Signup and view all the answers

    What type of query is sent when a server wants to map an IP address to a domain name?

    <p>Inverse query</p> Signup and view all the answers

    What happens when a server receives a query for a name that is not in its domain?

    <p>It searches its database for a server IP address</p> Signup and view all the answers

    What is the purpose of the in-addr node in the inverse domain?

    <p>To define IP addresses</p> Signup and view all the answers

    What is the relationship between the generic domains and the country domains?

    <p>They are separate sections of the domain name space</p> Signup and view all the answers

    What is the purpose of caching in DNS?

    <p>To reduce search time</p> Signup and view all the answers

    What is the purpose of time-to-live (TTL) in DNS?

    <p>To define the time a server can cache the information</p> Signup and view all the answers

    What is the consequence of a server caching a mapping for a long time?

    <p>It sends outdated mapping to the client</p> Signup and view all the answers

    What is the purpose of iterative resolution?

    <p>The client repeats the query to multiple servers</p> Signup and view all the answers

    How does a server handle a query for a mapping that is not in its cache?

    <p>It asks another server for the IP address</p> Signup and view all the answers

    What happens when a client queries multiple servers before it gets an answer?

    <p>Iterative resolution</p> Signup and view all the answers

    Why is caching problematic?

    <p>It may send outdated mapping to the client</p> Signup and view all the answers

    What is the purpose of a root server in the domain name space?

    <p>To delegate its authority to other servers</p> Signup and view all the answers

    What is the main difference between a primary and secondary server?

    <p>The way they obtain and update zone files</p> Signup and view all the answers

    What happens when a primary server fails?

    <p>The secondary server continues serving clients</p> Signup and view all the answers

    What is the purpose of having multiple root servers?

    <p>To provide redundancy for the data</p> Signup and view all the answers

    What type of server is responsible for creating and maintaining zone files?

    <p>Primary server</p> Signup and view all the answers

    What is the role of a secondary server in a domain?

    <p>To transfer the complete information from another server</p> Signup and view all the answers

    What is the relationship between a primary and secondary server?

    <p>One is responsible for creating zone files and the other is not</p> Signup and view all the answers

    What is the purpose of dividing a domain into smaller domains?

    <p>To delegate authority to lower-level servers</p> Signup and view all the answers

    What is the limitation of the initial DNS design?

    <p>The DNS was not able to handle dynamic changes to IP addresses</p> Signup and view all the answers

    Which protocol is used by DNS when the size of the response message is greater than 512 bytes?

    <p>TCP</p> Signup and view all the answers

    What is the purpose of the Dynamic Domain Name System (DDNS)?

    <p>To allow for dynamic changes to IP addresses</p> Signup and view all the answers

    What is the well-known port used by the DNS server?

    <p>Port 53</p> Signup and view all the answers

    How do secondary servers get notified about changes in the zone in passive notification?

    <p>They periodically check for any changes</p> Signup and view all the answers

    What is the purpose of authentication in DDNS?

    <p>To provide security and prevent unauthorized changes</p> Signup and view all the answers

    What information does an organization need to provide to register?

    <p>The name of its server and the IP address of the server</p> Signup and view all the answers

    What happens when the size of the response message is less than 512 bytes?

    <p>A UDP connection is used</p> Signup and view all the answers

    What is the main purpose of the inverse domain in DNS?

    <p>To map an IP address to a domain name</p> Signup and view all the answers

    What is the structure of the inverse domain based on?

    <p>The hierarchical structure of IP addresses</p> Signup and view all the answers

    What is the purpose of the country domains section in DNS?

    <p>To use two-character country abbreviations</p> Signup and view all the answers

    What is the first-level node in the inverse domain called?

    <p>arpa</p> Signup and view all the answers

    What is the purpose of the generic domains in DNS?

    <p>To define registered hosts according to their generic behavior</p> Signup and view all the answers

    What type of query is sent when a server wants to map an IP address to a domain name?

    <p>Inverse or pointer query</p> Signup and view all the answers

    What is the hierarchical structure of the inverse domain based on?

    <p>The IP address, with netid, subnetid, and hostid</p> Signup and view all the answers

    What is the purpose of the in-addr node in the inverse domain?

    <p>To define IP addresses</p> Signup and view all the answers

    What is the primary purpose of the Domain Name System (DNS)?

    <p>To map a domain name to an IP address and vice versa</p> Signup and view all the answers

    Why was the initial DNS design limited?

    <p>Because it was not designed to support a large number of hosts</p> Signup and view all the answers

    What is the purpose of a DNS client?

    <p>To map a domain name to an IP address</p> Signup and view all the answers

    What is the advantage of using DNS over a host file?

    <p>DNS is more scalable and can support a large number of hosts</p> Signup and view all the answers

    What is the purpose of the DNS server in the context of email?

    <p>To map an email address to an IP address</p> Signup and view all the answers

    What is the disadvantage of using a single host file to map domain names to IP addresses?

    <p>It would be too large to store in every host</p> Signup and view all the answers

    What is the relationship between the IP address and the domain name?

    <p>The IP address and the domain name are equivalent</p> Signup and view all the answers

    What is the role of the DNS in the Internet model?

    <p>To support other application programs</p> Signup and view all the answers

    What is the main reason for distributing the information among many DNS servers?

    <p>To reduce the load on the system</p> Signup and view all the answers

    What is a zone in the context of DNS?

    <p>A contiguous part of the entire domain name hierarchy</p> Signup and view all the answers

    What happens when a server divides its domain into subdomains?

    <p>The domain and zone refer to different things</p> Signup and view all the answers

    What is the purpose of creating a hierarchy of DNS servers?

    <p>To reduce the load on individual servers</p> Signup and view all the answers

    What is stored in the zone file of a DNS server?

    <p>All the information for every node under the domain</p> Signup and view all the answers

    Why is it not possible to store the entire domain name hierarchy on a single server?

    <p>Because it is too large</p> Signup and view all the answers

    What is the relationship between the original server and the servers at the lower levels?

    <p>The original server delegates part of its authority to the lower-level servers</p> Signup and view all the answers

    What is the purpose of dividing the domain name space into smaller domains?

    <p>To reduce the load on individual servers</p> Signup and view all the answers

    What happens when a server cannot resolve a query?

    <p>It returns the IP address of a new server to the client.</p> Signup and view all the answers

    What is the purpose of caching in DNS?

    <p>To store a mapping from another server and speed up resolution.</p> Signup and view all the answers

    What is the role of TTL in DNS?

    <p>To define the time a server can cache information.</p> Signup and view all the answers

    What happens if a server caches a mapping for a long time?

    <p>It may send an outdated mapping to the client.</p> Signup and view all the answers

    What is the result of iterative resolution?

    <p>The client repeats the query to multiple servers.</p> Signup and view all the answers

    Why is caching necessary in DNS?

    <p>To reduce the search time for a server IP address.</p> Signup and view all the answers

    What is the purpose of the authoritative server in DNS?

    <p>To provide authoritative answers to queries.</p> Signup and view all the answers

    What is the benefit of using caching in DNS?

    <p>It reduces the search time for a server IP address.</p> Signup and view all the answers

    What is the direction of reading domain labels in a domain name?

    <p>From bottom to top</p> Signup and view all the answers

    What is the purpose of a resolver in DNS?

    <p>To map a name to an address</p> Signup and view all the answers

    What happens when a local DNS server cannot resolve a query?

    <p>It refers the resolver to other servers or asks other servers directly</p> Signup and view all the answers

    What is the format of an IP address in a PTR query?

    <p>121.45.34.132.in-addr.arpa</p> Signup and view all the answers

    What is the relationship between a server serving a subnet and a server serving the whole site?

    <p>The server serving the whole site is at a higher level</p> Signup and view all the answers

    What is the direction of the resolution process in DNS?

    <p>From the root server to the client</p> Signup and view all the answers

    What is the purpose of the generic domains and country domains sections?

    <p>To organize the domain name space</p> Signup and view all the answers

    What is the process of mapping a name to an address or an address to a name called?

    <p>Name-address resolution</p> Signup and view all the answers

    Study Notes

    Domain Name System (DNS)

    • A domain name is a string of characters that represents an IP address
    • DNS is a hierarchical system that translates domain names into IP addresses

    FQDN (Fully Qualified Domain Name)

    • A domain name that contains the full name of a host
    • Includes all labels, from the most specific to the most general, that uniquely define the name of the host
    • Example: challenger.ate.tbda.edu
    • Must end with a null label, which is a dot (.)

    PQDN (Partially Qualified Domain Name)

    • A domain name that is not terminated by a null string
    • Starts from a node, but does not reach the root
    • Used when the name to be resolved belongs to the same site as the client
    • Resolver can supply the missing part, called the suffix, to create an FQDN
    • Example: Challenger can be defined as a partial name, and the resolver adds the suffix atc.jhda.edu to create an FQDN

    Domain

    • A subtree of the domain name space
    • The name of the domain is the domain name of the node at the top of the subtree
    • A domain may be divided into subdomains

    Distribution of Name Space

    • The information contained in the domain name space must be stored
    • It is inefficient and unreliable to have just one computer store the huge amount of information
    • A server can divide part of its domain and delegate responsibility to lower-level servers
    • The server still has a zone, but the detailed information is kept by the lower-level servers

    Root Server

    • A server whose zone consists of the whole tree
    • Does not store any information about domains but delegates its authority to other servers
    • Keeps references to those servers
    • There are several root servers, each covering the whole domain name space

    Primary and Secondary Servers

    • Primary server: stores a file about the zone for which it is an authority
    • Responsible for creating, maintaining, and updating the zone file
    • Stores the zone file on a local disk
    • Secondary server: transfers the complete information about a zone from another server (primary or secondary) and stores the file on its local disk
    • Neither creates nor updates the zone files

    Mapping Addresses to Names

    • A client can send an IP address to a server to be mapped to a domain name (PTR query)
    • DNS uses the inverse domain to answer queries of this kind
    • The IP address is reversed and the two labels in-addr and arpa are appended to create a domain acceptable by the inverse domain section

    Recursive Resolution

    • The client (resolver) can ask for a recursive answer from a name server
    • The resolver expects the server to supply the final answer
    • If the server is not the authority, it sends the request to another server (the parent usually) and waits for the response

    Iterative Resolution

    • If the client does not ask for a recursive answer, the mapping can be done iteratively
    • The server returns (to the client) the IP address of the server that it thinks can resolve the query
    • The client is responsible for repeating the query to this second server

    DNS Sections

    • Answer Section: includes the answer from the server to the client (resolver)
    • Authoritative Section: gives information (domain name) about one or more authoritative servers for the query
    • Additional Information Section: provides additional information that may help the resolver

    Types of Records

    • Question Record: used by the client to get information from a server
    • Resource Record: each domain name (each node on the tree) is associated with a record called the resource record
    • The server database consists of resource records

    Registrars

    • Commercial entities accredited by ICANN that add new domains to DNS
    • Verify that the requested domain name is unique and then enter it into the DNS database
    • A fee is charged

    Dynamic Domain Name System (DDNS)

    • Designed to respond to the need for dynamic updating of DNS records
    • When a binding between a name and an address is determined, the information is sent to a primary DNS server
    • The primary server updates the zone, and the secondary servers are notified
    • Uses an authentication mechanism to prevent unauthorized changes in the DNS records

    Domain Name System (DNS)

    • A central authority assigns the part of the domain name that defines the organization's nature and the organization's name.
    • The organization can add suffixes or prefixes to define its host or resources.
    • Hierarchical name space with an inverted-tree structure, with the root at the top and up to 128 levels.

    Domain Name Space

    • Each node in the tree has a label, a string with a maximum of 63 characters.
    • The root label is a null string (empty string).
    • Children of a node have different labels, ensuring uniqueness of domain names.

    Domain Name

    • A full domain name is a sequence of labels separated by dots (.).
    • Domain names are read from the node up to the root.
    • A full domain name always ends in a null label, which means the last character is a dot.

    Fully Qualified Domain Name (FQDN)

    • A label terminated by a null string is a fully qualified domain name (FQDN).

    DNS in the Internet

    • DNS is a protocol that can be used in different platforms.
    • The domain name space is divided into three sections: generic domains, country domains, and inverse domain.

    Generic Domains

    • Define registered hosts according to their generic behavior.
    • Each node in the tree defines a domain, which is an index to the domain name space database.

    Country Domains

    • Use two-character country abbreviations (e.g., "in" for India).
    • Second labels can be organizational or specific designations.

    Inverse Domain

    • Used to map an address to a name.
    • The inverse domain is added to the domain name space with the first-level node called "arpa" and the second level "in-addr".
    • The rest of the domain defines IP addresses.

    Resolution

    • Mapping a name to an address or an address to a name is called name-address resolution.
    • A resolver accesses a DNS server with a mapping request.
    • The resolver receives the mapping and interprets the response to see if it's a real resolution or an error.

    DNS Messages

    • Two types of messages: query and response.
    • Both types have the same format, with a header and question records, answer records, authoritative records, and additional records.
    • 12 bytes in length.
    • Contains identification subfield, flags subfield, number of question records, number of answer records, number of authoritative records, and number of additional records.

    Question Section

    • Consists of one or more question records.
    • Present in both query and response messages.

    Answer Section

    • Consists of one or more resource records.
    • Present only in response messages.
    • Includes the answer from the server to the client (resolver).

    Authoritative Section

    • Consists of one or more resource records.
    • Present only in response messages.
    • Gives information about one or more authoritative servers for the query.

    Additional Information Section

    • Consists of one or more resource records.
    • Present only in response messages.
    • Provides additional information that may help the resolver.

    Resource Records

    • Associated with each domain name (each node on the tree).
    • The server database consists of resource records.
    • Returned by the server to the client.

    Registrars

    • Commercial entities accredited by ICANN.
    • Verify that the requested domain name is unique and then enter it into the DNS database.
    • Charge a fee.

    DNS Overview

    • One solution to store host file information is to centralize it on a single computer, but this would create significant internet traffic.
    • Another solution, used by DNS, is to divide the information into smaller parts and store each on a different computer, allowing hosts to access the closest computer with the needed information.

    Name Space

    • Names assigned to machines must be unique and carefully selected from a name space with complete control over the binding between names and IP addresses.
    • A name space can be organized in two ways: flat or hierarchical.

    Flat Name Space

    • A flat name space assigns a name to an address without structure.
    • It cannot be used in a large system like the Internet because it must be centrally controlled to avoid ambiguity and duplication.

    Hierarchical Name Space

    • A hierarchical name space consists of multiple parts, defining the nature of the organization, the organization's name, and departments.
    • The authority to assign and control name spaces can be decentralized, with the original server delegating responsibility to lower-level servers.

    Zones and Domains

    • A server can divide its domain and delegate responsibility to other servers, keeping references to the delegated parts.
    • A zone is made up of detailed information for the part of the domain not delegated and references to the delegated parts.

    Root Server

    • A root server has a zone that consists of the whole tree.
    • It usually doesn't store domain information but delegates authority to other servers, keeping references to those servers.
    • There are multiple root servers distributed around the world.

    Primary and Secondary Servers

    • A primary server stores a file about the zone for which it is an authority and is responsible for creating, maintaining, and updating the zone file.
    • A secondary server transfers the complete information about a zone from another server and stores it on its local disk.
    • Both primary and secondary servers are authoritative for the zones they serve.

    DNS in the Internet

    • DNS is a protocol used in different platforms, dividing the domain name space into three sections: generic domains, country domains, and inverse domain.

    Generic Domains

    • Generic domains define registered hosts according to their generic behavior.
    • Each node in the tree defines a domain, which is an index to the domain name space database.

    Country Domains

    • Country domains use two-character country abbreviations, with second labels being organizational or specific designations.

    Inverse Domain

    • The inverse domain is used to map an address to a name, using a hierarchical structure with nodes for IP addresses.
    • The inverse domain is added to the domain name space with the first-level node "arpa" and the second-level node "in-addr".

    Caching

    • Caching reduces search time by storing query results in cache memory.
    • When a server receives a query, it checks its cache memory before sending the query to another server.
    • The server marks the response as unauthoritative if it comes from the cache memory.

    Time-to-Live (TTL)

    • TTL defines the time in seconds that a receiving server can cache the information.
    • After the TTL, the mapping is invalid, and any query must be sent again to the authoritative server.

    Dynamic Domain Name System (DDNS)

    • DDNS updates the DNS master file dynamically, responding to changes such as adding or removing hosts, or changing IP addresses.
    • In DDNS, the primary server updates the zone, and secondary servers are notified actively or passively.

    Summary

    • DNS can use either UDP or TCP, with a well-known port 53.
    • UDP is used when the response message is less than 512 bytes, and TCP is used when the response message is more than 512 bytes.

    Introduction to DNS

    • DNS is a supporting program that is used by other programs such as e-mail to map an e-mail address to the corresponding IP address.
    • The DNS client program sends a request to a DNS server to map the e-mail address to the IP address.
    • IP protocols use IP addresses to identify an entity, but people prefer to use names instead of numeric addresses.

    Hierarchical Structure of DNS

    • The solution to the problem of mapping names to addresses is to distribute the information among many computers called DNS servers.
    • The DNS servers form a hierarchical structure, with each server being responsible for a domain or a zone.
    • A zone is a contiguous part of the entire tree, and a server makes a database called a zone file and keeps all the information for every node under that domain.

    DNS in the Internet

    • DNS is a protocol that can be used in different platforms.
    • In the Internet, the domain name space (tree) is divided into three different sections: generic domains, country domains, and inverse domain.

    Generic Domains

    • Generic domains define registered hosts according to their generic behavior.
    • Each node in the tree defines a domain, which is an index to the domain name space database.

    Country Domains

    • Country domains use two-character country abbreviations (e.g., in for India).
    • Second labels can be organizational, or they can be more specific designations.

    Inverse Domain

    • The inverse domain is used to map an address to a name.
    • This type of query is called an inverse or pointer (PTR) query.
    • The servers that handle the inverse domain are also hierarchical.

    Resolution

    • Mapping a name to an address or an address to a name is called name-address resolution.
    • A host that needs to map an address to a name or a name to an address calls a DNS client called a resolver.
    • The resolver accesses the closest DNS server with a mapping request.

    Resolver

    • The resolver gives a domain name to the server and asks for the corresponding address.
    • If the server has the information, it satisfies the resolver; otherwise, it either refers the resolver to other servers or asks other servers to provide the information.

    Mapping Names to Addresses

    • Mostly, the resolver gives a domain name to the server and asks for the corresponding address.
    • If the domain name is from the generic domains section, the resolver receives a domain name such as "chal.atc.jhda.edu.".
    • If the domain name is from the country domains section, the resolver receives a domain name such as "ch.jhda.cu.ca.us.".

    Iterative Resolution

    • If the local server cannot resolve the query, it either refers the resolver to other servers or asks other servers directly.
    • This process is called iterative resolution because the client repeats the same query to multiple servers.

    Caching

    • Each time a server receives a query for a name that is not in its domain, it needs to search its database for a server IP address.
    • DNS handles this with a mechanism called caching.
    • When a server asks for a mapping from another server and receives the response, it stores this information in its cache memory before sending it to the client.

    Time-to-Live (TTL)

    • The authoritative server always adds information to the mapping called time-to-live (TTL).
    • TTL defines the time in seconds that the receiving server can cache the information.
    • After that time, the mapping is invalid and any query must be sent again to the authoritative server.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    ch3.pdf

    Description

    Understanding Fully Qualified Domain Names (FQDN) and their structure in DNS systems.

    More Like This

    Computer Networks Lecture 6: Electronic Mail and DNS
    32 questions

    Email Communication Process: Role of Email Server in Computer Networks

    WarmOnyx2042 avatar
    WarmOnyx2042
    Domain Name System (DNS) Introduction
    45 questions

    Domain Name System (DNS) Introduction

    ProdigiousQuantum avatar
    ProdigiousQuantum
    DNS Record Types
    38 questions

    DNS Record Types

    FoolproofTopaz avatar
    FoolproofTopaz
    DNS Resolution Process
    20 questions

    DNS Resolution Process

    InestimableCurl avatar
    InestimableCurl
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser