Systems Networking part 1 Flashcards
define internet and infranet
globally linked computer network using TCP/IP,
privately owned/controlled network, usually on a client/server platform to share files/data locally
OSI model
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
IPv4 address Exhaustion
and solutions?
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)
NIC Network Interface Card
provides a computer with connection to network.
implements physical layer circuitry to communicate with ethernet/wifi (data link layers).
MAC Address
Media Access Control address.
Unique ID assigned to NIC (Network Iterface Card)
Ethernet
technology that connects devices in a LAN or a WAN.
Hub
Node in Physical Layer. broadcasts every received packet to every device in the network.
Switch
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
ARP
Address REsolution Protocol. maps IP address to MAC address
Network Types: LAN and WAN
Local Area NEtwork and Wide Area NEtwork. o solid definition of what seperates the two; one’s a local network, the other is large.
IP Address and subnet mask
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)
CIDR
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.
vLAN
Virtual Area Network: specifically, allows a network to set a second internal virtual network.
NAT and PAT
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.
VPN
virtual Private network hides user’s IP address, and uses tunneling between user device and remote server
UDP/TCP
Transfer Control Protocol: TCP handshake, confirm arrival of each packet
User Datagram Protocol: fire and forget
Port
Virtual point where connection starts and ends. IP leads to the computer, but port leads to the process on the computer
Socket
an endpoint of a two-way communication between two files on a network. “a virtual file that can be read from and written to”
DHCP
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.
WHy use IP when we have MAC addresses?
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
What is ARP, ARP cache and Gratioutous ARP?
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.
What is the command used to show all open ports and socket connections on a machine?
netstat -an | grep LISTEN
lsof -i -n | grep LISTEN
nmap -v -A localhost
what is a subnet mask and what is it used for?
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)
DNS
DNS Record
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.
