Protocols Flashcards
TCP
Transmission Control Protocol
• 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
UDP
User Datagram Protocol
- 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
ICMP
Internet Control Message Protocol
• “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
SSH
Secure Shell
- Encrypted communication link - tcp/22
* Looks and acts the same as Telnet
DNS
Domain Name System
- 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
SMTP
Simple Mail Transfer Protocol
• 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
SFTP
Secure FTP
• Uses the SSH File Transfer Protocol - tcp/22
• Provides file system functionality
• Resuming interrupted transfers, directory listings,
remote file removal
FTP
File Transfer Protocol
- 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.)
TFTP
Trivial File Transfer Protocol
- udp/69
- Very simple file transfer application
- Read files and write files
- No authentication - Not used on production systems
Telnet
- Telnet – Telecommunication Network - tcp/23
- Login to devices remotely
- Console access
- In-the-clear communication
- Not the best choice for production systems
DHCP
Dynamic Host Configuration Protocol
• 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
HTTP and HTTPS
- Hypertext Transfer Protocol
- Communication in the browser
- And by other applications
- In the clear or encrypted
- Supported by nearly all web servers and clients
SNMP
Simple Network Management Protocol
- 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
RDP
Remote Desktop Protocol
- 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
NTP
Network Time Protocol
- 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
