Module 4 Flashcards
DNS
Domain Name System. A global and highly distributed network service that resolves strings of letters into IP addresses
Steps of Recursive Name Resolution
- Contact Root Server, which will return the TLD server that should be queried
- Contact the TLD server, which will respond with a redirect to authoritative server.
- Contact the authoritative server for that specific domain name
Name Resolution
The process of using DNS to turn a domain name into an IP address.
5 Types of DNS servers
- Caching name servers
- Recursive name servers
- Root name servers
- TLD Name servers
- Authoritative Name servers
Caching Name Server
Purpose is to store known domain name lookups for a certain amount of time
Recursive name servers
Performs full DNS resolution requests to discover correct IP for domain name.
Domain Name TTL
A value in seconds that can be configured by the owner of a domain name for how long a name server is allowed to cache an entry before it should discard it and perform a full resolution again
How many root servers are there and how are they distributed
13 distributed by across the globe through anycast, a technique used to route traffic to different destinations depending on factors like location, congestion, or link health
TLD
Top level domain. Represents the top of the hierarchical DNS name resolution system. it is the last part of a domain like .com, or .biz
What protocol does DNS use
UDP. DNS request can fit into a single UDP datagram.
Which port is DNS request sent to on the Caching server
53
DNS Resource Record Types
- A record
- AAAA record
- CNAME record
- MX record
- SRV record
- TXT record
A record
Used to point to certain domain name at a certain IPv4 IP address
Round Robbin
Iterating over a list of items one by one in an orderly fashion
Quad A record
Used to point to certain domain name at a certain IPv6 IP address
CNAME Record
Canonical Name Record.
Ensures that both microsoft.com and www.microsoft.com resolves to the same ip
MX record
Mail exchange record. Record is used in order to deliver email to the correct server
SRV Record
Defines the location of various specific services
TXT record
Text record. Often used to communicate configuration preferences about network services.
Like communicating configuration preferences to an email company that has been entrusted to handle emails services for your company
ICANN
The internet Corporation for assigned Names and Numbers.
Works in conjunction with the IANA to help define and control the global IP space and DNS
Domains
Used to demarcate where control moves from a TLD name server to an authoritative name server
Fully qualified domain name
FQDN. The combined parts of a domain name.
Registrar
A company that has an agreement with ICAN to sell unregistered domain names.
What is the character limit on a FQDN
255 characters
DNS zones
DNS zones are distinct, manageable segments of the Domain Name System (DNS) namespace, which is the hierarchical system responsible for translating human-readable domain names (like example.com) into IP addresses (like 192.0.2.1). DNS zones allow organizations to manage different parts of their domain independently, control how DNS queries are handled, and delegate authority to other entities if needed.
How are DNS zones configured
Zone files: Simple configuration files that declare all resource records for a particular zone. Zone files must contain and SOA Record and NS records.
SOA (Start of Authority) Record: Defines the authoritative DNS server for the zone, and includes important administrative information.
NS records: indicates other name servers that might also be responsible for this zone
Reverse lookup zone files
Let DNS resolvers ask for ran IP and get the GQDN associated with it returned
Pointer Record
PTS. Resolves an IP to a name
DHCP
Dynamic Host Configuration Protocol. An application layer protocol that automates the configuration process of hosts on a network.
Whenever a device connects to a network it will query the DHCP server and receive all the network configuration data it needs.
How do DHCP servers assign IP’s
Dynamic Allocation: The DHCP server assigns an IP address to a device for a limited period of time or until the device explicitly releases the IP address. How it Works: When a device connects to the network, it sends a DHCP request, and the server assigns an available IP address from a pool. The device is assigned a lease for this IP, which must be renewed periodically. Example Use Case: Home or office networks where devices come and go frequently (e.g., laptops, smartphones).
Automatic Allocation: The DHCP server permanently assigns an IP address to a device the first time it requests one. Once assigned, the IP address remains the same for that device, unless manually changed by an administrator. How it Works: When a device requests an IP address for the first time, the DHCP server assigns one from the available pool. The IP is retained for that device even if it disconnects and reconnects later.
Example Use Case: Networks where devices are generally static, but administrators prefer to automate the IP allocation.
Fixed Allocation: the DHCP server assigns a specific IP address to a device based on its MAC address. The IP address is always the same for that device whenever it connects to the network. How it Works: The administrator configures a mapping between the device’s MAC address and an IP address on the DHCP server. Whenever the device requests an IP, the server gives it the pre-assigned, fixed IP.
Example Use Case: Devices that require a consistent IP address, like servers, printers, or network infrastructure devices.
4 things every network needs to have configured
- IP Address
- Subnet Mask
- Gateway
- Name Server
DHCP Discovery
The process by which a client configured to use DHCP attempts to get network configuration information.
The DHCP Discovery Process
- A DHCPREQUEST message is sent via UDP from the client 0.0.0.0:68 to the server on 255.255.255.255:67
- The DHCP server will look at it’s configuration and make a decision on what IP address to offer the client.
- The server then sends a DHCPOFFER message from 192.168.1.1:67 to 255.255.255.255:68
DHCP Lease
The amount of time an Ip address is leased to a specific device by the DHCP server. When the lease expires, the device will have to request a new Ip from the DHCP server.
NAT
Network Address Translation (NAT) is a method used by routers to modify the IP address information in the headers of packets as they pass through a network. NAT allows multiple devices on a local network (using private IP addresses) to access the internet using a single public IP address. It is essential for reducing the number of public IP addresses needed and adds a layer of security to the local network.
IP masquerading
When a router hides the source ip by replacing it with it’s own ip
Devices within a local network are assigned private IP addresses (such as 192.168.x.x or 10.x.x.x).
When a device with a private IP wants to send a request to the internet, the router modifies the private IP and port number to the public IP (and a different port, if necessary).
The router keeps track of this translation in a NAT table so that it can route any return traffic to the correct private IP.
When the response from the internet arrives, the router looks up the entry in its NAT table and forwards the response to the correct internal device.
Port Preservation
Port preservation refers to the process by which Network Address Translation (NAT) maintains the original source port number of a connection when it translates the internal (private) IP address to a public IP address. This ensures that the port used on the internal device remains the same as it passes through the NAT device to communicate with external systems.
Port forwarding
Port forwarding is a networking technique that allows an external device on the internet to communicate with a specific device inside a private local network by routing traffic through a router. It essentially opens up a specific port on your router and forwards incoming connections to a particular device in the internal network, making services hosted behind the router accessible from the outside.
VPN
A VPN (Virtual Private Network) is a service that creates a secure, encrypted connection between your device and a remote server over the internet. By routing your internet traffic through this encrypted tunnel, a VPN helps ensure privacy, security, and anonymity online.
It provides:
- Encryption
- IP Masking
- Remote or Proxy servers to hide location.
Reverse Proxy
Distributes incoming requests
A service that might appear to be a singe server to external clients, but actually represents many servers living behind it.
Proxy Service
A server that acts on behalf of a client in order to access another service
