TCP/IP Basics Flashcards by William Carosella

IP Packet

Composed at Layer 3, includes IP info and payload from Layer 4

Gets encapsulated at Layer 2

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Internet Control Message Protocol

ICMP

Important role in error reporting and diagnostics

Operates at Layer 3

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Transmission Control Protocol

TCP

Connection-oriented protocol

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User Datagram Protocol

UDP

Connectionless protocol

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Three way handshake

Part of TCP

SYN - SYN-ACK, ACK

Sender sends syn, receiver responds with syn-ack, sender sends final ack

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Main TCP Header parts

Source Port - Destination Port - Sequence Number - Acknowledgement Number

Will also include:

Flags: individual bits that give info on state of connection
Checksum - recipient can use this to validate data

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User Datagram Protocol

UDP

Unlike with TCP, data does not get segmented in Layer 4.

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UDP Datagram Header

Source port - destination port - length - checksum

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Universal Broadcast MAC Address

FF-FF-FF-FF-FF-FF

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CLI terms to get IP and MAC on:

MacOS
WinOS
Linux

ifconfig
ipconfig /all
ip (or ifconfig, but that is depreciated)

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Bits in an IP(v4) address?

4 octets

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Network ID

The shared portion of clients on a LAN

client unique portions will be written as a 0

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Default Gateway

IP address of the router for a LAN

Frequently will be given the lowest or highest possible IP address within the network ID range

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Subnet mask

Series of ones followed by zeroes

The ones stop where the network ID stops in dotted decimal, generally.

Computers can compare their IP with another against the subnet mask - if they are identical up to where the ones stop, they share the same subnet.

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Address Resolution Protocol

ARP

An ARP request broadcasts to all MAC addresses on LAN. Sends destination IP, gets a response from destination IP with corresponding destination MAC, allows NIC to create frame with destination now

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CIDR notation

/[NUMBER]

Number = the number of ones in the subnet mask

Automatically know the subnet mask from CIDR notation

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IP Class Blocks

Sections of IP addresses distributed out to ISPs

Class A addresses

First octet 1-126

Subnet mask always 255.0.0.0

Binary always starts with 0xxxxxxx.

Class B addresses

first octet 128-191

Subnet mask always 255.255.0.0

Binary always starts with 10xxxxxx.

Class C addresses

first octet 192-223

Subnet always 255.255.255

Binary always starts with 110xxxxx.

Class D addresses

First octet 224-239

Binary always starts with 1110xxxx.

Class E addresses

First octet 240-255

Binary always starts with 1111xxxx.

Multicast

Sending a packet to a group of specific computers from one source

Anycast

sending a packet to the nearest computer of a pool that share the same address

CIDR

Classless Interdomain routing

Subnet Host Calculation

2^x - 2 x = number of 0s in the subnet mask's binary representation Remember - subnet masks always have 32 digits, so just subtract the /number from 32 to get your 0s.

Available Subnet Calculation

Start with your Network ID and convert to binary Then move to the right y number of digits 2^y = the number of subnets you are creating

Manual Dotted Decimal to Binary Conversion

128 64 32 16 8 4 2 1 If the number in your dotted decimal is greater than the leftmost number above, subtract the left-most number from dotted decimal value. Assign a 1 to the first binary value. Take remaining value and place it above next value. If it is more, follow same process. If not, assign a 0 to the respective binary value and move on down the line.

Convert binary to dotted decimal

128 64 32 16 8 4 2 1 Write the binary under each number, add the numbers that have a 1 under them.

4 basic network assignment principles

1) Default gateway should get the first or last IP address in the network ID 2) Try to use IP addresses in sequential order 3) Separate servers from clients - keep servers in blocks of addresses 4) Document it all

DHCP Server Port DHCPS Client Port

UDP - 67 UDP - 68

DHCP Scope

the pool of available IP addresses it can give out

DHCP Relay

Feature of routers to take a DHCP client's discovery broadcast and send it as unicast to a known DHCP server on the network

IP Helper Address UDP Helper Address

The IP address of the DHCP server given to routers so they can relay broadcasts

IP Exclusion Range

A subset of IP addresses you tell the DHCP server not to assign dynamically, setting them aside for static reservation devices (printers, servers, cameras, etc.

MAC Reservations

reserving IP addresses on a DHCP server using MAC addresses of clients - any time they get a request from that MAC, they know what to give already

APIPA

IP in the range of 169.254.0.0/16 Automatic Private IP Addressing, happens when a DHCP server is unreachable

DHCP Release/Renewals for: Windows MacOS Linux

ipconfig /release ipconfig /renew sudo ifconfig eth0 down sudo ifconfig eth0 up sudo dhclient -r sudo dhclient

DHCP Failover

A pair of DHCP servers that share the same scope, provide redundancy for large enterprises

Rogue DHCP Server

A DHCP server connected to the network that is handing out incorrect IP addresses and/or default gateways. Can be used in cyberattacks

Private IP address Blocks

Class A: 10.0.0.0 - 10.255.255.255 Class B: 172.16.0.0-172.31.0.0 Class C: 192.168.0.0-192.168.255.255