1.8 An Overview of DNS
What is the order of a DNS request?
1. Your local host device - the resolver - requests a name resolution. This request is sent to your host's local name server, that you have designated. 2. If your local name server doesn't know, it queries a root server. 3. The root server's response is sent to your local name server.
What is a computer domain?
A domain contains a group that can be administered with a common set of rules.
What is a Fully Qualified Domain Name, or FQDN?
A fully qualified domain name, sometimes also referred to as an absolute domain name, is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System. It specifies all domain levels, including the top-level domain and the root zone.
A DNS server is a database with RESOURCE RECORDS, or RR. These database records offer many different DNS services and contain over 30 record types. What does an A record tell you?
An A record query is the most common query of the DNS database. It defines the IPv4 address of a host. In other words: the A record supplies the IP address for a human readable domain name. The AAAA records do the same thing, but for IPv6 addresses.
What's the difference between an NS record and a PTR record?
An NS record specifies which server is the authoritative server for given host. A PTR record is the exact opposite of an A record. The A record supplies the IP address for a human readable domain name. The PTR record give you the domain name if you have the IP address.
There is also a T2 Timer. This timer tells the client to search for a new DHCP server if the original server is unavailable. At what time does the T2 Timer initiate looking for a new DHCP server?
At 87.5 % of the lease term. This can also be said as 7/8th.
Every device to include switches, routers, firewalls, servers, and workstations have there own internal clock. Why is synchronizing this clock critical?
Authentication information like Kerberos is based on tickets that expire. Log files are used to track important things like outage details.
How do we avail a DHCP server to be utilized by a host on a different subnet?
DHCP Relay or, IP Helper, will direct the router to transmit a UNICAST to a host in need on a different subnet.
More about corporate domains.
Domains are used to divide areas of responsibility or departments of a corporation. The domain is specified when mapping a network computer to a drive.
Good info part 2.
If you host your own emails, you'll need to configure SPF and DMARC by entering TXT records into your DNS records. Otherwise, your email will end up in the destination Spam folder.
Stratum 1 clients synchronize to stratum 0 servers also called primary time servers. Stratum 2 synch to what?
stratum 1 servers
NTP servers respond to time requests from NTP clients. Your distance from the original reference clock is measured in what?
stratum layers.
How accurate is an NTP server on a local network?
Less than 1 millisecond.
What is the record that tells you the name of the mail server, not the IP address, but the name of the server?
MX record. Mail exchanger record.
What is a Mail Exchanger record?
MX stands for mail exchanger. An MX record is a type of DNS record, so any understanding of MX records has to begin with an understanding of the fundamentals of the Domain Name System.
What is an MX record?
Mail exchanger records are DNS records that facilitate email delivery to your email address. An MX record is used to tell other devices where emails sent to your domain should be routed.
How does the TXT record provide security?
Mail servers check that the incoming mail really did come from an authorized host. They use Sender Policy Framework, SPF protocol, to prevent mail spoofing.
What is a Name Server Record or NS Record?
NS stands for nameserver, and the nameserver record indicates which DNS server is authoritative for that domain.
Are domains intended for home users?
No, domains are not intended for home users. Only computers running a Professional or Enterprise version of Windows can be joined to a domain.
Why does the owner of a website need a TXT file that contains a bunch of plain text in their DNS records?
The TXT record was originally intended to add human readable notes or documentation to a domain, but has morphed into other functions such as providing domain name ownership and secure Email communication.
What is the big benefit of a DHCP Relay for a large company?
The administrators don't need a DHCP server on every subnet. They can relay to a couple for redundancy.
What technology did DHCP replace in 1997?
The bootstrap protocol, aka BOOTP.
DHCP servers lease IP addresses to hosts. The length of these lease times vary. Something called a T1 timer changes the status from a bound time to a renewal time. What is the default time for the client to check in with the lending DHCP server to renew the IP address?
The default is 50% of the lease time.
DHCP servers have a limited communication range because their broadcast stops at what?
The router.
How many DNS root server clusters are there?
There are 13 IP addresses that go to many root servers. This is called the root zone.
There are Many DNS servers. What are some examples?
There are hundreds of top-level domain servers like: .com, .org, .net, .edu, .gov.
What are some examples of service records or S R V?
Windows Domain Controller - like LDAP, instant messaging server, VOIP controller.
Is there a misconception about root servers?
Yes, the misconception is that there are only 13 root servers in the world. In reality there are many more, but still only 13 IP addresses used to query the different root server networks.
When hosting a website, you will need to configure DNS how?
You will need to create A and CNAME records, which point your website name or domain name to the IP address of the server hosting the website files.
What protocol does MX use?
Simple Mail Transfer Protocol, SMTP, the standard protocol for all email.
What is a pointer record, PTR, in a Domain Name System?
A record that resolves an IP address to a domain or host name. The opposite of an A record which points a domain name to an IP address.
If one physical server offers multiple services it may have multiple different names leading to the same record. What is this name record called?
Canonical name record or CNAME. A Canonical Name record is a type of resource record in the Domain Name System that maps one domain name to another. This can prove convenient when running multiple services from a single IP address.
What else can IPAM do to help administrators?
Control reservations and identify shortages.
What is IPAM is IP Address Management. What benefits does it add?
One console allows an administrator to track, configure, and plan all DHCP on the network. It reports upcoming renewal times, usage, and allocation.
How many country code top-level domains or ccTLDs like .us, .ca, .uk, are there?
Over 275
DNS primarily function is to translate human-friendly domain names into their numeric IP address equivalents. But, it has many other uses, list some.
Proving domain name ownership. eMail verification.
What are the individual database records of domain name services called?
Resource Records or RR.
The Atomic clock or GPS clock is called what?
Stratum 0
What does a TXT record do?
TXT records allow an administrator to store text on a domain. A TXT record can be used to associate arbitrary text with a host to provide information about a server, network, data center, or other.
How does SPF work?
TXT records are used to provide DKIM to digitally sign your outgoing mail, which can be validated by mail servers.
Good info part 1.
TXT records can be used to fight Email Spam by ensuring that emails sent from a specific domain indeed originated from that domain.
What is the other DNS resource record you will need?
TXT.
What is the term automatic allocation in the DHCP server environment?
The DHCP server keeps a list of past assignments and it issues the same IP addresses if they are available. The key phrase here is - when available. It's not mandatory like a static assigned address.
What is a DNS A record?
The IPv4 address of a host.
How does the Mail Exchanger Record record work?
The MX record indicates how email messages should be routed. X the standard protocol for all email. Like CNAME records, an MX record must always point to another domain.
What does DNS do?
Translates human-readable names into computer-readable IP addresses.
True or False: One console can manage both IPv4 and IPv6 DHCP?
True
True or False: a TXT record can be used to put your public key in the DKIM TXT record?
True
True or False: A Name Server Record, or NS record points to the name of a server
True.
True or False: Like CNAME records, an MX record must always point to another domain?
True.
How do you find the TXT record of a domain?
Use a command line tool. Linux can use dig. Windows can use nslookup.
