Computer Networking: A Top-Down Approach, CH2

TCP

(Transmission control protocol)

APP: DNS record format

(name, value, type, TTL)

APP: DNS record types

A = hostname, IP address; CNAME = canonical alias, canonical name; NS = domain, authoritative hostname; MX = mailserver name

APP: POP3 Phases

Authorization (Client: user, pass; Server: OK, ERR) and Transaction (list, retr, dele, quit)

APP: DNS header flags

Query or reply, recursion desired/available; reply is authoritative

APP: Local DNS

does not belong to hierarchy, aka default name server, each ISP has one, host query sent to local dns, acts as proxy

DNS

domain name system

APP: Conditional GET

don't send object if cache has up-to-date cached version

FTP

file transfer protocol , transfer file to/from remote host

non-persistent connections

type of HTTP connections that closes after each request from the client

APP: HTTP Status codes

200 (OK), 301 (Moved Permanently), 400 (Bad request), 404 (Not found), 505 (http version not supported), 304 (Not Modified)

APP: DNS caching

Caches mappings with a TTL, TLDs usually cached in local name servers so root not often visited

2 application architectures

Client-server, P2P

APP: 3 DNS Attacks

DDoS, Redirect, Exploitation

APP: Resource Record

DNS record

APP: What transport service does an app need?

Data integrity (reliable data tranfer), timing (low delays), throughput (bandwidth), security (encryption)

APP: Methods in HTTP 1.0

GET, POST, HEAD(asks server to leave requested object out of response)

APP: Methods in HTTP 1.1

GET, POST, HEAD, PUT( uploads file in entity body to path specified in URL field) , DELETE (deletes file specified in the URL field)

APP: How do cookies keep state?

HTTP messages carry state . protocol endpoints: maintain state at sender/receiver over multiple transactions

APP: Redirect Attack

Man-in-middle (intercept queries); DNS poisoning (send bogus requests that cache)

APP: User agent

Outlook, iPhone mail client, browser

APP: Mail access protocols

POP (Post Office Protocol - authorization and download), IMAP (Internet Mail Access Protocol - manipulation of msgs)

APP: 2 Ways to upload form input

POST method - uploaded to server in entity body; URL method - GET method - uploaded in URL field of request line

APP: Process

Program running within host, in same host (inter-process communication), in different host (exchange messages)

APP: Why use caching?

Reduce response time, reduce traffic, enables poor content providers to deliver content

APP: How to insert records in DNS?

Register name with DNS registrar; Provide names, IP address of authoritative name server; Registrar inserts 2 RRs into TLD (NS and A); Create A and MX record

APP: Exploit DNS for DDoS

Send queries with IP spoofing , Requires amplification

APP: Tit-for-Tat

Sends chunks to peers sending chunks at highest rate, every 30 seconds randomly unchoke another peer

Describe client-server architecture

Server - always on, permanent IP address, data centers; Client - communicate with server, dynamic IP address, do not communicate directly with each other

APP: How does cache act as server and client?

Server for client, Client for original server

APP: SMTP

Simple mail transfer protocol, port 25, uses TCP to send message

HTTP vs FTP

They both run on top of TCP. The differente - FTP uses two parallel TCP connections to transfer a file, a control connectionand a data connection

UDP

User Datagram Protocol) is an alternative communications protocol to Transmission Control Protocol (TCP)

APP: DDoS

bombard root servers with traffic, but mostly unsuccessful because root is bypassed; instead, bombard TLD servers

APP: Interated DNS query

contacted server replies with name of server to contact

APP: Describe BitTorrent

file divided into 256Kb chunks, tracker tracks peers, torrent - groups of peers exchanging chunks, churn - peers come and go, request rarest chunk first

APP: 4 Cookie Components

header line in response, header line in request, cookie kept on user's host, back-end database

APP: DNS services

hostname to IP address translation, host aliasing, mail server aliasing, load distribution

APP: HTTP

hypertext transfer protocol, web application layer protocol, client request objects, server sends objects, uses TCP, port 80

APP: How do you address processes?

identifier (host IP address and port number)

APP: Client process

initiates communication

APP: Mail server

mailbox (incoming messages), message queue (outgoing messages), SMTP protocol (to send messages)

APP: Persistent HTTP

multiple objects sent over single TCP connection (3RTT - handshake, base HTML (web page), objects)

APP: Describe P2P architecture

no always-on server,end systems directly communicate , peers request service from other peers, provide service in return to other peers( self scalability - new peers bring new service capacity, as well as new service demands) and peers are intermittently connected and change IP addresses (complex management)

APP: Non-persistent HTTP

one object sent over TCP connection , downloading multiple objects required multiple connections (2RTT per object, browsers often open parallel TCP connections)

APP: Authoritative DNS

organizations DNS servers, maintained by organization or service provider

APP: Recursive DNS query

puts burden of name resolution on contacted name server

APP: What does TCP service provide?

reliable transport, flow control, congestion control,does not provide: timing, minimum throughput guarantee, security and connection-oriented

APP: 2 types of HTTP messages

request, response

FTP commands, responses

sample commands: USER ,PASS , LIST ,RETR filename , STOR filename sample return codes 331 -OK, 125- transfer starting , 425- Can't open data connection ,452- Error writing file

APP: Goal of web caches

satisfy client request without involving origin server

APP: What cookies are used for?

shopping carts, , authorization recommendations, user session state

APP: Why not centralize DNS?

single point of failure, traffic volume, distant centralized database, maintenance

APP: RTT

time for packet to travel from client to server and back

APP: TLD

top-level domain servers; Network Solutions maintains .com, Educause maintains .edu

persistent connections

type of HTTP connections that keeps connections open after a request to the server

APP: What do application-layer protocol define?

types of message, message syntax, message semantics, process rules

APP: UDP

unreliable data transfer

APP: 3 Email components

user agent, mail server, SMTP

APP: Server process

waits to be contacted

APP: Proxy server

web cache

APP: Socket

where process sends/receives messages to/from