DNS/DHCP Guide

DeMultiplexing

Taking in all traffic all aimed at the same node and delivering it to the proper receiving services

Multiplexing

Delivering traffic from multiple services (zoom, spotify) and packaging it to a single node

TCP header: data offset

Will determine where the payload begins

Router

a hardware device that directs traffic/forwards data packets to its intended destination

TCP header: sequence number

determines the order of bytes

TCP header: checksum

determines data intergity. Makes sure no data was lost or corrupt during transmission

TCP: acknowledgement number

provides the next expected segment

TCP socket state

1. LISTEN
   Server is listening for requests

2. SYN_SENT
   Client sent a SYN flag and is waiting to receive SYN-ACK

3. SYN_RECIEVE
   Server receIved SYN and sent SYN-ACK. Now waiting for final ACK

4. ESTABLISHED
   Connection is established and data can be sent between the two nodes
   

interface

a physical hardware device/software that connects two or more systems/devices. A network interface is a router that connects to the internet.

Each router has a unique IP address to its corresponding network

T or F: DNS servers must be configured on a node on a network to work

TRUE

5 TYPE of DNS servers

Caching, Recursive, TLD, root name, authorative name

Caching and Recursive name servers

Store domain name lookups for a certain amount of time to speed up future requests. TTL (time to live).

DNS round robin

Multiple IP addresses associated with a single domain

A Record

points a domain name to IPV4 addresses

Quad A Record

points a domain name to IPV6 addresses

CNAME Record

redirects traffic from one domain to another

MX Record

Directs emails to the correct mail server

SRV Record

defines location of specific servers

Three parts of a fully qualified domain

sub domain: example: www
domain: example: google
TLD(Top-Level-Domain): example: .com

What would it mean if the DNS server fails

It means that when you type a hostname the computer cannot resolves its IP aadress so users cannot get to websites through domain names

Purpose of DHCP

To configure IP addresses, subnet masks, gateway router, and DNS servers which in turn reduces manual set up

DHCP: Dynamic Allocation, Automatic Allocation, and Fixed Allocation

Dynamic: The IP addresses may differ each time a device connects to the internet
Automatic: Assign the same IP address to the device if possible
Fixed: The IP address is assigned based on a MAC table

authorative name server

holds the official DNS record

How does DNS lookup work

1. if the web browser cannot find the ip addr of the domain check cache server

2. check resolver server and look at their cache server

3. it will send the queuer to the next level the root server — (13 servers across the world) (it wouldn’t know the ip address it will direct to TLD server)

4. the TLD server would have the address information but not the ip address (it will direct resolver to authorative name server)

5. the authorative name server would know the ip address

DHCP lease

the amount of time an IP address is assigned to a computer

DHCP discover

a client gets their network configuration information

NAT

allowd for the router/firewall to change source ip address on outgoing packets. This masquerading of IP allows for the source ip to be hidden