Internet Protocols and Services Review

Flashcards covering key vocabulary terms and concepts related to internet protocols, network architecture, and common services, based on the provided lecture notes.

End System

A device connected to the Internet that runs applications. Examples include web servers and iPhones.

Router

A network device that forwards data packets between computer networks.

Internet Service Provider (ISP)

A company that provides Internet access to organizations and individuals.

Application Programming Interface (API)

A set of defined rules that enable different applications to communicate with each other.

Protocol

A set of rules that govern how data is formatted, transmitted, and received in a network.

Network Protocol Purpose

To define the rules and conventions for communication between network devices.

Access Network (DSL, cable, fiber)

The part of the network that connects end systems to the edge router of an ISP.

DSL vs. Cable

DSL uses existing phone lines, while cable uses existing TV coaxial cable lines for internet access.

Cable vs. Fiber (FTTH)

Cable Internet uses coaxial cables, while Fiber-to-the-Home (FTTH) uses optical fiber directly to the user's home, offering typically higher speeds.

Dual-homed

A system or network connected to two separate networks or ISPs, providing redundancy.

Home Network Components

Includes devices like routers, modems, switches, and various end systems (computers, smartphones, smart devices).

Packet-Switching

A network communication method where messages are broken into smaller units called packets, which are then transmitted independently and reassembled at the destination.

Store-and-Forward

A packet-switching technique where a router must receive the entire packet before it can begin transmitting the first bit of the packet onto the outbound link.

Packet Loss Causes

Occurs when packets arrive at a full queue in a router, leading to the packet being dropped.

Network Core Functions

Routing (determining end-to-end paths) and Forwarding (moving packets from a router's input to its output).

Point of Presence (POP)

An access point from one place to the rest of the Internet, often where ISPs connect.

ISP Interconnection Points

ISPs interconnect at Internet Exchange Points (IXPs) or through peering agreements.

Packet Delays (at each router)

Processing delay, queuing delay, transmission delay, and propagation delay.

Transmission Delay vs. Propagation Delay

Transmission delay is the time required to push all packet's bits onto the link, while propagation delay is the time it takes for a bit to travel from one end of the link to the other.

Queuing Delay Causes

Occurs when packets wait in a router's queue for their turn to be transmitted onto the outgoing link, especially when arrival rate exceeds departure rate.

End-to-End Delay

The total time it takes for a packet to travel from the source host to the destination host, including all processing, queuing, transmission, and propagation delays.

Ping Tool

A network utility used to test the reachability of a host and measure the round-trip time (RTT) for messages sent from the originating host to a destination computer.

Traceroute Tool

A network diagnostic tool used to display the path (route) and measure transit delays of packets across an Internet Protocol (IP) network.

Throughput

The rate at which bits are transferred between sender and receiver.

Bottleneck Link

The link in the end-to-end path that has the lowest available throughput, thus limiting the overall data transfer rate.

Internet Protocol Layers

Application, Transport, Network, Link, Physical (from top to bottom).

HTTP Layer

Application layer.

End System Protocol Layers

All five layers: Application, Transport, Network, Link, Physical.

Router Protocol Layers

Network, Link, Physical layers.

Transport Layer Data Unit

Segment.

Link Layer Data Unit

Frame.

Client-Server Architecture (Always-on)

The server side is typically 'always-on'.

Client-Server Architecture (First Contact)

The client side makes the first contact.

Socket

A software endpoint for communication, typically identified by an IP address and a port number.

Socket Addressing Elements

IP address and port number.

Default HTTP Port

Port 80.

Default Apple WAC Port (Back to My Mac)

Port 4500.

Default SSH TCP Port

Port 22.

Application-Level Protocol

Defines how applications running on different end systems pass messages between themselves. Examples include HTTP, SMTP, FTP.

Email Transport Protocol (and reason)

Email (SMTP) uses TCP because it requires reliable data transfer.

UDP Use Cases (lack of reliability)

Applications use UDP when speed and low overhead are more important than guaranteed delivery, such as for streaming multimedia, DNS, or online gaming.

HTTP Message Types

Request messages (sent by clients) and Response messages (sent by servers).

HTTP Protocol State

HTTP is a stateless protocol, meaning the server maintains no information about past client requests.

HTTP Request Message Information

Includes request line (method, URL, HTTP version), header lines (Host, User-Agent, Accept-Language, etc.), and sometimes entity body.

GET vs. POST HTTP Methods

GET requests typically retrieve data and append form data to the URL, while POST requests send data to be processed (e.g., submitting form data) in the message body.

HTTP Response Message Information

Includes status line (HTTP version, status code, phrase), header lines (Date, Server, Last-Modified, Content-Length, Content-Type, etc.), and entity body (requested object).

HTTP Redirect Status Code

3xx series, commonly 301 (Moved Permanently) or 302 (Found).

Redirect New URI Location

In the 'Location:' header field of the HTTP response.

HTTP Status Code 404

Not Found - the requested resource could not be found on the server.

HTTP Status Code 200

OK - the request has succeeded.

Steps to Retrieve HTML (Non-Persistent HTTP)

Client initiates TCP connection -> Client sends HTTP request -> Server sends HTTP response -> Server closes TCP connection -> Client processes response.

Cookie Purpose

To allow websites to store stateful information (e.g., user preferences, login status) on the client side (browser) across multiple HTTP requests.

HTTP Response Cookie Header

'Set-Cookie:'.

HTTP Request Cookie Header

'Cookie:'.

Session vs. Persistent Cookie

A session cookie is deleted when the browser closes, while a persistent cookie is stored on the user's hard drive and remains until its expiration date.

HTTP Status Code 304

Not Modified - the client's cached copy of the resource is still valid, so the server does not need to send the object again.

Last-Modified Header

Indicates the date and time at which the origin server believes the resource was last modified. Used for caching.

HTTP Requests to Proxy Server

All HTTP requests from a client configured to use a proxy server.

Proxy Cache Hit Action

Serves the object directly from its cache to the client and checks if the cached object is up-to-date with the origin server (using conditional GET).

Proxy Cache Miss Action

Sends a request to the origin server, receives the object, forwards it to the client, and stores a copy in its cache.

Proxy Cache Validation

It uses a conditional GET request to the origin server, typically with 'If-Modified-Since' header, using the 'Last-Modified' date of its cached object.

FTP Control Channel Type

Out-of-band control.

Passive vs. Active FTP

In active FTP, the client sends its port to the server and the server initiates the data connection, while in passive FTP, the server tells the client which port to connect to for data, and the client initiates the data connection.

Client-to-Mail Server Protocol

SMTP (Simple Mail Transfer Protocol).

Mail Server-to-Server Protocol

SMTP (Simple Mail Transfer Protocol).

Email Binary Attachments Encoding

Binary attachments are encoded into 7-bit ASCII using mechanisms like MIME (Multipurpose Internet Mail Extensions) before being sent via SMTP.

SMTP Security (Default)

By default, SMTP is not secure; information, including usernames and passwords, is typically not encrypted.

Email Access Protocols

POP (Post Office Protocol), IMAP (Internet Message Access Protocol), and HTTP (for webmail).

Hostname vs. IP Address

A hostname is a human-readable label (e.g., google.com), while an IP address is a numerical label (e.g., 172.217.160.142) that identifies a device on a network.

DNS Resolution vs. TCP Connection

DNS name resolution occurs before the TCP connection setup because the client needs the IP address of the server to initiate the TCP connection.

Canonical Hostname

The true, official name for a host, often distinct from aliases or frequently used names (e.g., www.example.com might have a canonical name like server.example.com).

DNS Load Distribution

A hostname can resolve to multiple IP addresses, and DNS servers can rotate the order of these IP addresses in responses, distributing requests among multiple servers.

Distributed DNS Rationale

A distributed DNS system offers better scalability, reliability (no single point of failure), manageability, and lower traffic volume compared to a centralized system.

Root, TLD, and Authoritative DNS Servers

Root servers point to TLD (Top-Level Domain) servers (.com, .org); TLD servers point to authoritative DNS servers; and authoritative DNS servers hold the DNS records for specific domains (e.g., example.com).

Local DNS Server

A DNS server used by an organization or ISP, acting as a proxy. It receives queries from hosts and forwards them to other DNS servers, and caches results.

Recursive vs. Iterative DNS Query

In a recursive query, a DNS server takes full responsibility to resolve the name, while in an iterative query, a DNS server replies with the name of another DNS server to contact.

DNS Caching Benefits

By storing previously resolved DNS responses, caching reduces the need to query root, TLD, and authoritative servers repeatedly, thus lowering their load and improving resolution speed.

DNS Resource Record Types

A (hostname-IP address mapping), NS (authoritative name server), CNAME (canonical name for an alias), and MX (mail server).

NS RR Value Field

The domain name of the authoritative name server for the indicated domain.

MX RR Name Field

The alias hostname for the mail server (e.g., smtp.example.com).

RR TTL Field

Time To Live - indicates how long (in seconds) the resource record can be cached by a local DNS server.

Multiple RRs in DNS Response

Yes, a single DNS response can contain multiple resource records.

DNS Reply Sections

Question (query being made), Answer (resource records that directly answer the query), Authority (resource records for authoritative servers), and Additional (helper RRs for the authoritative servers).

DNS Attacks

DDoS attacks, Man-in-the-middle attacks, DNS Cache Poisoning, Domain Hijacking.

Transport-Layer Packet Name

Segments.

Internet Transport Layer Protocols

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Transport Layer vs. Network Layer

The transport layer provides logical communication between processes on different hosts, while the network layer provides logical communication between hosts.

TCP Services

Reliable data transfer, connection-oriented service, flow control, congestion control, and byte-stream service.

Multiplexing (Transport Layer)

The process of gathering data from multiple application-layer processes, encapsulating them with header information, and passing them to the network layer.

Demultiplexing (Transport Layer)

The process of delivering segmented data from the network layer to the correct application-layer process on the receiving host, using port numbers.

Port Numbers Location

Transport layer header.

UDP Socket Identification

By the destination IP address and destination port number.

TCP Socket Identification

By the source IP address, source port number, destination IP address, and destination port number (a 4-tuple).

UDP Guarantees

No, UDP provides no guarantees for reliable data transfer, flow control, or congestion control.

Application Protocol Using UDP

DNS or Streaming applications (e.g., VoIP).

UDP for Streaming Rationale

Lower overhead, faster transmission due to no connection setup or retransmission delay, and tolerance for some packet loss.

Adding Reliability to UDP Applications

Reliability must be built into the application layer itself if desired.

UDP Header Size

8 bytes.

Reliable Data Transfer Protocol Responsibility

To ensure that data sent by the sender is delivered correctly and in order to the receiving application process.

TCP Connection-Oriented Meaning

TCP requires a handshake process to establish a connection between two processes before data can be exchanged, and then a teardown process to close it.