4.7 DNS Flashcards
What is a forward lookup address
finds the IP address for a given host name
What is a revers lookup
finds the host name from a given IP address.
What is a root dns server
hold information for the root zone (.). Root servers answer name resolution requests by supplying the address of the corresponding top-level DNS server
. (dot) domain
The . (dot) domain, the root domain, denotes a fully qualified, unambiguous domain name.
Top-Level Domain (TLD)
A TLD is the last part of a domain name (for example, .com, .edu, .gov). TLDs are managed by the Internet Corporation of Assigned Names and Numbers (ICANN).
Fully Qualified Domain Name (FQDN)
The FQDN includes the host name and all domain names separated by periods. The final period (which is for the root domain) is often omitted and implied.
Additional domains (Second-level domains)
Additional domains are second-level domains that have names registered to an individual or organization for use on the internet.
Host Name
The host name is the part of a domain name that represents a specific host. For example, www is the host name of www.example.com.
Records
are used to store entries for host names, IP addresses, and other information in the zone database.
Authoritative Server
An authoritative server is a DNS server that has a complete copy of all the records for a particular domain.
Dynamic DNS (DDNS)
DDNS enables clients or the DHCP server to update records in the zone database. Without dynamic updates, all A (host) and PTR (pointer) records must be configured manually.
What is recursion?
the process by which a DNS server uses root name servers and other DNS servers to perform name resolution.
What is the first step in recursion
The host looks in its local cache to see if it has recently resolved the host name.
What is the second step in recursion
If the information is not in the cache, it checks the Hosts file. The Hosts file is a static text file that contains host-name-to-IP address mappings.
What is the third step in recursion?
If the IP address is not found, the host contacts its preferred DNS server. If the preferred DNS server can’t be contacted, the host continues contacting additional DNS servers until one responds.
What is the fourth step in recursion
The host sends the name information to the DNS server. The DNS server checks its cache and Hosts file. If the information is not found, the DNS server checks any zone files that it holds for the requested name.
What is the fifth step in recursion
If the DNS server can’t find the name in its zones, it forwards the request to a root zone name server. This server returns the IP address of a DNS server that has information for the corresponding top-level domain (such as .com).
what is the sixth step in recursion
The first DNS server requests the information from the top-level domain server. The server returns the address of a DNS server with the information for the next highest domain. This process continues until a DNS server is contacted that holds the necessary information.
What is the seventh step in recursion
The DNS server places the information in its cache and returns the IP address to the client host. The client host also places the information in its cache and uses the IP address to contact the desired destination device.
router(config)#ip host [name] a.b.c.d
Creates static DNS entries.
router(config)#ip domain-name [name]
Configures the router default domain (for DNS).
router(config)#ip name-server a.b.c.d
Sets the default DNS name server.
router(config)#ip domain-lookup
Enables the router to use DNS to identify IP addresses from hostnames.
router(config)#no ip domain-lookup
Disables the broadcast name resolution of hostnames.
router#show hosts
Displays a list of known IP hosts.
Where does a Device Details Router or Switch DNS name resolution looks for information and in what order
Static DNS entries
DNS server query (if enabled)
Where does a Workstation DNS name resolution looks for information and in what order
Local DNS cache
HOSTS file
DNS server query (Primary)
DNS server query (Secondary)
