Chapter 2 Flashcards
User vs network oriented application layer protocols:
User = interact with end user
network = manage network
Why was LDAP implemented
Lightweight Directory Access Protocol:
Simplify access control to various applications being used on a network
3 Different types of network architecture:
1) Client-server
2) Peer-to-Peer
3) N-tier
What is a daemon?
Server software that starts when computer is started until shut down
What is the drawback of the Client-server network architecture?
Client always initiates communication
Fix: Peer-to-peer architecture
What is good about P2P ( Peer-to-peer ) networks?
No central server
Workloads shared among all nodes
Challenges of a P2P network?
Security + management
What is the 4 email protocols:
X.400
SMTP
POP3
IMAP4
What standard does the x.400 refer to?
ITU-T standards
What are the different elements that could be in a X.400 header?
C = country
A = admin management domain
P = private management domain
O = organization name
OU = organization unit
G = Given name
I = Initials
S = surname
How does x.400 notation look like
“I=J;S=Doe;O=acme;OU=sales;A=sapo;C=za”
Who will this x.400 email be sent to?
“I=J;S=Doe;O=acme;OU=sales;A=sapo;C=za”
J Doe who works at Acme in sales in south africa. sapo = south african post office
What does smtp stand for?
Simple mail transfer protocol
What rfc is SMTP defined by?
5321
What does smtp use to handle messages?
“agents”
What are the 2 agents in smtp?
MUA (mail user agent) MTA (mail transfer agent)
What is used to transfer an email for one UA to another UA?
1+ mta’s ( since the email needs to be transferred from one user to another )
What is the task of the MUA in SMTP?
Simply a piece of code that accepts a message and forwards it to a MTA ( sender )
Accept incoming mail and store in directory (receiver )
What is the task of the MTA in SMTP?
Find a route from sender to receiver and forward email along that route.
How do you indicate which MTA you would prefer to use?
Using the “preference”
What do MTA’s add to emails they process?
A header line “Received: “
What is the first thing you send to the SMTP server once you have connected to it?
HELO or EHLO ( extended hello )
How do you indicate who the email is from in SMTP?
MAIL FROM:
How do you indicate who the recipient of an email is with SMTP
RCPT TO:
What do you send to a SMTP server when you want to send data?
DATA
How do you end the email off with SMTP?
Single “.” on its own line
How do you terminate the connection with a SMTP/POP3 server?
QUIT
Which port is used to communicate between MTA’s?
25
What is the SMTP submit port and its port number?
- When email software speaks to 1st MTA
What is the most common protocol used for web based email software?
POP3
What protocols do typical email programs combine?
SMTP + POP3
How do you enter the username on a POP3 server?
USER username
Does POP3 need auth? What about SMTP?
SMTP = no. POP3 = yes
How do you enter your password on a POP3 server?
PASS password
How do you retrieve/delete the 1st message on a POP3 server?
RETR 1 or DELE 1
What port does POP3 servers use?
110
What does POP3 stand for?
Post office protocol version 3
What does IMAP4 stand for?
Internet Message Access Protocol v4
How does IMAP4 “show” messages?
When a user clicks on a email it downloads it from the server and then displays it on the computer. But it remains stored on the server
Why is IMAP better than POP3?
POP3 permanently stores the downloaded emails, but now we want to view it on multiple devices hence IMAP4 is used more often
Key words for an IMAP session:
LOGIN, SELECT (folder), FETCH (message, can be used with ALL, FULL, FAST), TERMINATE
What does ALL FULL and FAST do?
ALL = everything about the email besides the body
FULL = ALL + body
FAST = flags + date + size but no header/email body
What does the \deleted, \answered, \seen flags indicate?
Deleted = true if the message is deleted.
same for the rest
Port number for IMAP servers?
143
Why were virtual terminals developed?
To connect remotely to another computer over the network
Why is telnet bad?
Because username and password is transmitted as clear text
what port does telnet use?
Port 23
What do you use if you want to echo ( view ) the characters you enter on a virtual terminal?
set localecho.
What happens if you dont “set localecho”.
you wont see anything you enter ( if remote computer doesnt echo the characters )
Problem with set localecho?
Password will be displayed as you log in
What is a trusted virtual terminal protocol?
SSH
Which port is SSH?
22
commands to upload/download files with FTP?
get,put,mget,mput
What will mput * abc * do?
upload all files with names that contain abc in the current client directory
What does “get” correlate to on the FTP server?
RETR
What does “put” correlate to on the FTP server?
STOR
Does browsers contain functionality that corresponds to mget, put or mput?
No
What was the special username used to download public files?
anonymous ( yes actually anonymous)
What is the control connection port of FTP?
21
What is the data connection port of FTP?
20
What is PASV mode in FTP?
A different way to connect to FTP server.
Usually data channel is from server to client ( problems with firewall ) But with pasv client connects to server with data channel
What is the only requests a web server has to support?
GET and HEAD
What port does HTTP use?
80
What port does HTTPS use?
443
At what layer does HTTPS use encryption?
HT(T)PS = transfer = transport layer = layer 4
Best known tool to sniff traffic?
WireShark
When sniffing traffic, which layer’s packet will you sniff?
Layer 2 ( but 3-7 packets would also be included as a payload ( builds from 7 - 1)
