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70 Cards in this Set
- Front
- Back
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Host table |
Local file matching IPs to hostnames. No longer actively used but still possible
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Name resolution
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Using DNS servers to convert host names into IP addresses
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3 elements of DNS
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DNS name spaceName ServersName resolvers
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DNS Name Space
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Tree-structured name space -- each branch of the tree IDs a domain. Each domain contains a collection of resource records which contain host names & IPs.
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Name Servers
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DNS server -- application that maintains info about the domain tree structure and authoritiative info about one or more specific domains in that structure.
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Resolvers
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Client program that generates DNS queries and sends them to a DNS server for fulfillment.
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Each host is uniquely identified by what?
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A host name and domain name combination.
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Examples of top level domains
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.com .net. .org etc
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What is the second level domain in this host name:www.google.com
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googlewww is the host namecom is the TLD
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FQDN
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Fully qualified domain name - complete DNS name for a computer.Host namesecond-level domain nametop-level domain name
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What is the authoritative source for a domain?
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The DNS server(s) responsible for maintaining that domain's resource records
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Root Name Servers
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Highest-level DNS servers in the entire namespace. Maintain information about the top-level domains. Ultimate source for allDNS info.
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gTLDs
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Six Generic top level domains at a level directly below root name servers. There are more now but these are what we started with.com .edu etc
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Name the gTLDs
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comedugovmilnetorg
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gTLD use: com
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commercial orgs
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gTLD use: edu
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four-year degree-granting ed institution in N. America
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gTLD use: gov
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US government institutions
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gTLD use: mil
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US military institutions
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gTLD use: net
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Networking organiations
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gTLD use: org
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Noncommercial orgs
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Which gTLDs do you need some sort of certification to obtain
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edugovmil
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Which gTLDs can you get without any special process
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comorgnet
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ICANN
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Internet Corporation for Assigned Names and NumbersResponsible for accreditation of domain name registrars and ratification of new top-level domains.
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In the DNS hierarchy which level has no hosts?
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The TLD and root levels do not have hosts outside of the DNS servers that exist to point other DNS servers in the right direction.
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ccTLD
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Country code TLDsTwo-letter TLDs for specific countries in their own language.
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IANA
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Internet Assigned Numbers AuthorityDepartment of ICANN
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What is the ccTLD for the United States
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.us
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Who administrates the US ccTLD?
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Information Sciences Institute of the University of Southern California
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What is the second level domain in this URL?www.google.com
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Google
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How many DNS servers must you provide a registrar to maintain a second level domain?
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2
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What is the max size of a second-level domain name?
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63 characters
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What is the max size of an entire FQDN?
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255 characters
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Which transport layer protocol does DNS use
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UDP
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What port does DNS operate?
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53
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Five sections of a DNS message
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HeaderQuestionAnswerAuthorityAdditional
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DNS message section: header
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Contains info about the nature of the message
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DNS message section: question
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Information requested from the destination server
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DNS message section: answer
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Contains resource records supplying the information requested in the question section
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DNS message section: authority
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contains resource records pointing to an authority for the information requested in the question section
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Every DNS message type has a header but the remaining sections only appear if
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There are data to put in them.These sections are not always relevant.
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DNS message section: additional
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contains resource records with additional info in response to the question section
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A DNS message can contain more than one what?
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More than one of each section.
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What happens if a dns message is too large to fit in a UDP datagram?
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The two systems establish a standard TCP connection over port 53 to transmit the data
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How do local DNS servers speed to process of resolving IPs from hostnames?
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Caching the IPs of a FQDN.Caching the IPs of a TLD authoritative server and the IPs of second-level domain authoritative servers saving steps for the next similar requests
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Negative Caching
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When a DNS server retains info about names that do not exist in a domain.This speeds the process the next time a user attempts to resolve a hostname that does not exist -- DNS does not need to start all over again at the root name server
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TTL
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Time to live.The max time data can be cached on a DNS server
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Who specifies TTL?
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Admins of the authoritative DNS server for a domain
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Referral
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The process by which one DNS server sends a name resolution request to another dns server.
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Two types of name resolution requests
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Recursive queryiterative query
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DNS Forwarder
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One server that functions as a 'proxy' for all DNS requests to another DNS server.
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Reverse name resolution
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Convert an IP into a DNS name
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What service does reverse name resolution use?
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in-addr.arpa...Which has four sub-sub domains able to represent the first three octets of every IP address
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What are the bare minimum capabilities of a DNS server
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Receiving queriesSending queries to other DNS servers
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caching-only server
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A DNS server that is not authoritative for any domain. Just receives requests and sends those requests to other DNS servers
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Dynamic update standards for DNS
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Allows a DHCP server to notify a DNS server that an address has been changed and tell the DNS server how to modify its records
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Zone
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administrative entity you create on a DNS server to represent a discrete portion of the DNS namespace
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Three types of zones
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primarysecondarystub
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Primary zone
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The primary source for information at a given zone. Maintains an active database locally.
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Secondary zone
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The secondary source of info at a given zone. Must get its information from the primary zone.
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Stub zone
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Only a source of information on the authorities of this zone.
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7 types of resource records used by DNS servers
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SOANSAAAAAPTRCNAMEMX
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Resource Record: SOA
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Start of AuthorityIndicates that the server is the best authoritative source for data concerning the zone. Each zone must have a SOA record. Only one SOA record per zone
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Resource Record: NS
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Name ServerIDs a DNS server functioning as an authority for the zone. Each DNS server (primary or secondary) in a zone must be represented by an NS record.
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Resource Record: A
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AddressProvides a name-to-address mapping that supplies IPv4 address for a DNS name.
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Resource Record: AAAA
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Provides a name-to-address mapping that supplies IPv6 address for a specific DNS name.
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Resource Record: PTR
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PointerProvides address-to-name mapping that supplies DNS name for address in the in-addr.arpa domain.
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Resource Record: CNAME
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"Canonical NameCreates an alias that points to the canonical name (the ""real"" name) of a host identified by an A record."
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Resource Record: MX
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Mail ExchangerIDs a system that directs email traffic sent to an address in the domain to the individual recipient
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Root Hints
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Names an addresses of multiple root name servers often preconfigured on a DNS server
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How many root name servers are there?
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13 |
