Protocols

Question 1

TCP

Transmission Control Protocol

Answer 1

• Connection-oriented
• A formal connection setup and close
• “Reliable” delivery
• Recovery from errors
• Can manage out-of-order messages
or retransmissions
• Flow control
• The receiver can manage how much data is sent

Question 2

UDP

User Datagram Protocol

Answer 2

• Connectionless
• No formal open or close to the connection
• “Unreliable” delivery - No error recovery
• No reordering of data or retransmissions
• No flow control
• Sender determines the amount of data transmitted

Question 3

ICMP

Internet Control Message Protocol

Answer 3

• “Text messaging” for your network devices
• Another protocol carried by IP - Not used for data transfer
• Devices can request and reply to administrative requests
• Hey, are you there? / Yes, I’m right here.
• Devices can send messages when things don’t go well
• That network you’re trying to reach
is not reachable from here
• Your time-to-live expired, just letting you know

Question 4

SSH

Secure Shell

Answer 4

• Encrypted communication link - tcp/22

* Looks and acts the same as Telnet

Question 5

DNS

Domain Name System

Answer 5

• Converts names to IP addresses - udp/53
• www.professormesser.com = 162.159.246.164
• These are very critical resources
• Usually multiple DNS servers are in production

Question 6

SMTP

Simple Mail Transfer Protocol

Answer 6

• SMTP - Simple Mail Transfer Protocol
• Server to server email transfer - tcp/25
• Also used to send mail from a device to a mail server
• Commonly configured on mobile devices
and email clients
• Other protocols are used for clients to receive email
• IMAP, POP3

Question 7

SFTP

Secure FTP

Answer 7

• Uses the SSH File Transfer Protocol - tcp/22
• Provides file system functionality
• Resuming interrupted transfers, directory listings,
remote file removal

Question 8

FTP

File Transfer Protocol

Answer 8

• tcp/20 (active mode data), tcp/21 (control)
• Transfers files between systems
• Authenticates with a username and password
• Full-featured functionality (list, add, delete, etc.)

Question 9

TFTP

Trivial File Transfer Protocol

Answer 9

• udp/69
• Very simple file transfer application
• Read files and write files
• No authentication - Not used on production systems

Question 10

Telnet

Answer 10

• Telnet – Telecommunication Network - tcp/23
• Login to devices remotely
• Console access
• In-the-clear communication
• Not the best choice for production systems

Question 11

DHCP

Dynamic Host Configuration Protocol

Answer 11

• Automated configuration of IP address,
subnet mask and other options
• udp/67, udp/68 - Requires a DHCP server
• Dynamic / pooled
• IP addresses are assigned in real-time from a pool
• Each system is given a lease
• Must renew at set intervals
• Reserved
• Addresses are assigned by MAC address
• Quickly manage addresses from one location

Question 12

HTTP and HTTPS

Answer 12

• Hypertext Transfer Protocol
• Communication in the browser
• And by other applications
• In the clear or encrypted
• Supported by nearly all web servers and clients

Question 13

SNMP

Simple Network Management Protocol

Answer 13

• Gather statistics from network devices
• udp/161
• v1 – The original
• Structured tables, in-the-clear
• v2 – A good step ahead
• Data type enhancements, bulk transfers
• Still in-the-clear
• v3 – The new standard
• Message integrity, authentication, encryption

Question 14

RDP

Remote Desktop Protocol

Answer 14

• Share a desktop from a remote location over tcp/3389
• Remote Desktop Services on many Windows versions
• Can connect to an entire desktop or just an application
• Clients for Windows, MacOS, Linux, iPhone, and others

Question 15

NTP

Network Time Protocol

Answer 15

• Switches, routers, firewalls, servers, workstations
• Every device has its own clock - udp/123
• Synchronizing the clocks becomes critical
• Log files, authentication information, outage details
• Automatic updates
• No flashing 12:00 lights
• Flexible - You control how clocks are updated
• Very accurate
• Accuracy is better than 1 millisecond

Question 16

SIP

Session Initiation Protocol

Answer 16

• Voice over IP (VoIP) signaling
• tcp/5060 and tcp/5061
• Setup and manage VoIP sessions
• Call, ring, hang up
• Extend voice communication
• Video conferencing, instant messaging, file transfer,
etc.

Question 17

SMB

Server Message Block

Answer 17

• Protocol used by Microsoft Windows
• File sharing, printer sharing
• Also called CIFS (Common Internet File System)
• Direct over tcp/445 (NetBIOS-less)
• Direct SMB communication over TCP
without the NetBIOS transport

Question 18

POP/IMAP

Answer 18

• Receive emails from an email server
• Authenticate and transfer
• POP3 - Post office Protocol version 3 - tcp/110
• Basic mail transfer functionality
• IMAP4 - Internet Message Access Protocol v4 - tcp/143
• Manage email inbox from multiple clients

Question 19

LDAP/LDAPS

Answer 19

• LDAP (Lightweight Directory Access Protocol) - tcp/389
• Store and retrieve information in a network directory
• LDAPS (LDAP Secure) - tcp/636
• A non-standard implementation of LDAP over SSL

Question 20

H.323

Answer 20

• Voice over IP (VoIP) signaling - tcp/1720
• ITU Telecommunication H.32x protocol series
• Setup and manage VoIP sessions
• Call, ring, hang up
• One of the earliest VoIP standards
• Still in use today

Question 21

DNS

Domain Name Service

Answer 21

• Translates human-readable names
into computer-readable IP addresses
• You only need to remember
www.Amazon.com
• Hierarchical
• Follow the path