TCP/IP Applications Flashcards
session
any singular communication between 1 computer & another
TCP
transmission control protocol
enables-connection oriented communication
TCP 3-way handshake
client sends a single SYN (synchronize) packet to server
server gets packet > returns single SYN, ACK (synchronize, acknowledge) packet
client then sends server a single ACK packet > immediately requests that server begin sending requested data
TCP sequence following 3-way handshake
server finishes sending requested data > sends FIN (finished) packet
client responds with ACK > sends its own FIN
server responds with ACK
session closed
UDP
user datagram protocol
short distance communication - integrity not important
DHCP (ports)
domain host control protocol
clients - UDP 67
servers - UDP 68
NTP / SNTP (ports)
network time protocol / simple network time protocol
synchronize clocks of devices on the network
enter IP address of NTP/SNTP server
UDP 123
TFTP
Trivial File Transfer Protocol
enables transfer of files using UDP from 1 machine to another
UDP port 69
No data protection > computers on same LAN
ICMP
Internet Control Message Protocol
works at layer 3 to deliver connectionless packets
disconnect messages
ping
echo request / reply
single ICMP packet sent by ping command
response to echo request (no firewall)
destination host unreachable
computer has no route to the address listed
request timed out
no echo reply is generated before the 1-second default time limit
ICMP queries may be blocked by firewall
unreachable default gateway
ICMP issues on exam
ping default gateway > destination host unreachable
Ping of Death
malformed ping packets
patched long ago > term is on exam
IGMP
Internet Group Management Protocol
enables routers to communicate with hosts to determine a “group” membership
multicast range
Small subnet of Class D (224/4)
224.0.0.0/4
IGMP group
multicast does not assign IP addresses to individual hosts
multicast group is assigned to a 224.0.0.0/4 address
devices in this group tell upstream router or switch that they wish to receive multicast messages
port numbers
16-bit values between 0 & 65535
well-known port numbers
numbers between 0 & 1023
reserved for specific TCP/IP applications
ephemeral port numbers
1024 - 5000
dynamic (private) port numbers
49152 - 65535
IANA recommened ephemeral port numbers
49152-65535
registered ports
1024 - 49151
socket (endpoint)
session information (IP address & port number) stored in the RAM for TCP/IP session (single computer)
socket pairs (endpoints)
connection data stored on 2 computers about the same connection
connection (session)
whole connection
command to list endpoints currently stored on a device
“netstat -n”
open (listening) port
socket that is prepared to respond to any IP packets destined for that socket’s port number
command to list listening ports
“netstat -an”
local address 0.0.0.0
open port works on all NICs
displayed this way even if computer only has 1 NIC
foreign address 0.0.0.0
no other computers are currently connected
established ports
active, working endpoint pairs
close_wait
shows graceful closure in which each side of the conversation sees the session closing normally
command to see which app is sending specific communication
“netstat -ano”
process ID
every program running on your computer gets a number used by the OS to track all running programs
command to see the NAME of a specific program sending a communication
“netstat -b”
HTML
Hypertext Markup Language
XML
Extensible Markup Language
HTTP
Hypertext Transfer Protocol
underlying protocol used by the web
runs on TCP port 80 by default
IIS
Internet Information Services
Microsoft’s web server platform
Apache HTTP Server
Web server software run on the majority of UNIX / Linux boxes
~ 50% of active Web site on the Internet
Active site
web site that is functioning by serving Web pages
Parked sites
domain names that have been purchased / registered but don’t really do anything (Web or e-mail servers)
web clients
browsers
read Web pages supplied by web servers
URL
Uniform Resource Locator
complete name of the Web server (IP or DNS generated)
downside to open ports
security vulnerability
requirements for secure Internet app
authentication
encryption
norepudiation
autentication
user name & password
encryption
jumbling data so it can’t be read as plain text
nonrepudiation
source is not able to deny a sent message
SSL
Secure Sockets Layer
protocol developed by Netscape for transmitting private documents over the Internet
how SSL works
public key is used to encrypt communication
encrypted communication is sent over a SSL connection
Decrypted at the receiving end using a private key
supported by all popular Web browsers & servers (HTTPS)
HTTPS
Hypertext Transfer Protocol over SSL
uses TCP port 443
“Hypertext Transfer Protocol Secure”
TLS
Transport Layer Security
more powerful replacement for SSL
operates functionally the same
Telnet Protocol
legacy protocol used to access different mainframes from a singular dumb terminal
TCP port 23
no encryption
SSH
Secure Shell
terminal emulation program that looks exactly like Telnet but encrypts the data and the authentication
TCP port 22
host name
name or IP address of the computer to which you want to connect
primary function of Telnet & SSH
enable control of a remote computer from a local computer over a network
e-mail operational basics
e-mail sent to address
stored in electronic mailbox on e-mail server
tell e-mail client to download the message
SMTP
Simple Mail Transfer Protocol
protocol used by clients to send e-mail messages
TCP port 25
POP3
Post Office Protocol version 3
1 / 2 protocols that receive e-mail from SMTP servers
TCP port 110
IMAP4
Internet Message Access Protocol version 4
2 / 2 protocols that receive e-mail from SMTP servers
supports searching server for key words & creating folders
TCP port 143
Web services
Gmail, Google Docs, Google Sheets, etc.
Sendmail
Linux / UNIX
no interface
Microsoft Exchange
Windows only
SMTP & POP3 capable
e-mail server
accept incoming mail
sort mail for recipients into individual storage area mailboxes
kick back messages without known recipient
e-mail client
programs that run on a computer to enable sending, receiving, & organizing of e-mail
e-mail client communications
SMTP server - send mail
IMAP or POP server - download messages from mail server
FTP
File Transfer Protocol
original protocol used on the Internet for transferring files
more reliable & faster than HTTP
can transfer with security & data integrity
FTP ports
Active (legacy) - TCP ports 20 & 21
Passive - TCP port 21
FTP site types
Anonymous - anyone can log on
Secured - credentials required
FTP server
stores files
accepts incoming transmissions
verifies login credentials
transfers files
FTP client
logs in to FTP site (Web site, command line, or FTP app)
downloads requested files onto local hard drive
Most Web servers are also FTP servers
bundled versions are not as robust
FTP limitations
not encrypted by default
most anonymous FTP sites limit the number of users that may download to ~ 500 at a time
using browser at FTP client
“ftp://
some browsers limit features > Firefox only allows for anonymous logins
active FTP
client sends FTP request out on port 21
FTP server responds - directed back to an ephemeral port using port 20
does not work with NAT & firewalls (do not recognize the incoming communication from port 20 as originating from within the network)
passive FTP
client sends FTP request out on port 21
server sends back a random port number - telling client which port to listen on for data requests
client sends data to the port specified
client initiates the conversation - NAT router knows where to send incoming packets
client needs to be configured to expect incoming packets from passive FTP
TFTP
Trivial File Transfer Protocol
transfers files using UDP port 69
no credentials
never use on non-secure networks
