Systems Networking part 1

Question 1

define internet and infranet

Answer 1

globally linked computer network using TCP/IP,

privately owned/controlled network, usually on a client/server platform to share files/data locally

Question 2

OSI model

Answer 2

first standard model for network communications describing 7 layers:

Application Layer: human-computer interaction. FTP and SMTP for file transfer and mail transfer

Presentation Layer: formats data to be understood by application layer. ASCII to to Unicode, encryption/decryption. HTTP to transmit web pages, SSL to transpit secure data.

Session: maintains connections, decides ports/services. manages data flow, terminates connections,

Transport: data transmission, confirms data is received successfully. TCP UDP

Network Layer: provides data routing from source to destination. determines best path to travel. decide travel path for email from source to destination. (IP protocol)

Data Link Layer: error detection/correction. adds error-check bits to data and checks on the other side. ensures data is not transmitted too quickly for other side to handle.

Physical Layer: defines electrical/mechanical specifications of how data is physically transported. converts an email into electric signals to travel over a cable

Question 3

IPv4 address Exhaustion

and solutions?

Answer 3

we are running out of the 4.29 billion 32-bit IPv4 addresses we had available.

NAT/PAT helps slow the issue down, but not for long.

IPv6 is coming, using 128-bit addresses, allowing 2^128 combinations (maybe 340 undecillion times more addresses than IPv4)

Question 4

NIC Network Interface Card

Answer 4

provides a computer with connection to network.

implements physical layer circuitry to communicate with ethernet/wifi (data link layers).

Question 5

MAC Address

Answer 5

Media Access Control address.

Unique ID assigned to NIC (Network Iterface Card)

Question 6

Ethernet

Answer 6

technology that connects devices in a LAN or a WAN.

Question 7

Hub

Answer 7

Node in Physical Layer. broadcasts every received packet to every device in the network.

Question 8

Switch

Answer 8

Data Link Layer Networking Device. floods entire network with “unknown unicast frame” (packet that id doesn’t know who to send to). each unknown host reponds by sending their own frame. thus, swithc learns MAC address of each host.

Forwarding: Switch knows destionation MAC, sends it there

Filter: if frame source and destination ports are same, kill frame

Question 9

ARP

Answer 9

Address REsolution Protocol. maps IP address to MAC address

Question 10

Network Types: LAN and WAN

Answer 10

Local Area NEtwork and Wide Area NEtwork. o solid definition of what seperates the two; one’s a local network, the other is large.

Question 11

IP Address and subnet mask

Answer 11

numbers that identify a device on a network, Net ID for network/router id, host id for hosts on the network.

submet mask: 32-bit number, created by setting host bits to 0 and network bits to 1. (255.0.0.0)

Question 12

CIDR

Answer 12

Class-less Inter-domain Routing.

IP-assignment method. groups blocks of addresses into single routing-table entries, which reduces routing table size and allows an organization to have more machines under the same IP.

Question 13

vLAN

Answer 13

Virtual Area Network: specifically, allows a network to set a second internal virtual network.

Question 14

NAT and PAT

Answer 14

method of translating private IP addresses to public IP addresses.

static NAT: one-to-one mapping of private IP to public IP for devices that need to be accessile from the internet (web servers)

dynamic NAT: one-to-many mapping of private IP to many public IP addresses. for devices like laptops that do not need to be accessible by the internet.

PAT: Port Address Translation: special type of dynamic NAT mapping multiple private IP addresses to a single public IP address by using their ports.

Question 15

VPN

Answer 15

virtual Private network hides user’s IP address, and uses tunneling between user device and remote server

Question 16

UDP/TCP

Answer 16

Transfer Control Protocol: TCP handshake, confirm arrival of each packet

User Datagram Protocol: fire and forget

Question 17

Port

Answer 17

Virtual point where connection starts and ends. IP leads to the computer, but port leads to the process on the computer

Question 18

Socket

Answer 18

an endpoint of a two-way communication between two files on a network. “a virtual file that can be read from and written to”

Question 19

DHCP

Answer 19

Dynamic Host Configuration Protocol.

client/server protocol.

automatically provides IP address to devices (hosts) on a network. you know, instead of manually assigning an internal ip address to each machine.

Question 20

WHy use IP when we have MAC addresses?

Answer 20

MAC addresses are not globally unique (different manufacturers reuse these numbers)

MAC addresses are not hierarchical which doesn’t help create effitient packet travel routes across networks

Question 21

What is ARP, ARP cache and Gratioutous ARP?

Answer 21

Address Resolution Protocol, maps IP to MAC adress.
The cache is a collection of ARP entries.
Qrauitious ARP: when a node/host anounces to update its IP-MAP-Mapping to the entire network.

Question 22

What is the command used to show all open ports and socket connections on a machine?

Answer 22

netstat -an | grep LISTEN

lsof -i -n | grep LISTEN

nmap -v -A localhost

Question 23

what is a subnet mask and what is it used for?

Answer 23

32-bit number that divides IP addess into the network ID and host ID. used to segment a network into smaller networks (VPNs. raise security and reduce network traffic)

Question 24

DNS

DNS Record

Answer 24

Domain Name System. Maps domain name to IP address.

DNS Record: Domain Name -> IP matched pairs. Stored in DNS servers, DNS root name servers and top-level domain servers.