OSI Model Flashcards
What does the Application Layer handle?
Provides services directly to user applications. Types of communications. i.e. Email, file transfer, client/server.
What does the presentation layer do?
Performs data transformations to provide a common interface for user applications, including services such as reformatting, data compression and encryption (i.e. ASCII to EBCDIC, BCD to Binary)
What does the Session layer do?
Establishes, manages and ends user connections and manages the interaction between end systems. Services include things like establishing communications as full or half duplex.
What does the Transport Layer do?
Insulates the three upper layers from having to deal with the complexities of layers 1 - 3 by providing the functions necessary to guarantee a reliable network link. This layer also provides error recovery and flow control between the two end points of the network connection.
What does the Network Layer do?
Establishes, maintains and terminates network connections. Routes data to different LAN’s and WAN’s based on network address
What does the Data-Link Layer do?
Ensure the reliability of the physical link established at layer 1. Standards define how data FRAMES are recognized and provide necessary flow control and error handling at frame level
What does the Physical layer do?
Controls transmission of the raw bitstream over the transmission medium. Standards for this layer define parameters as signal voltage swing, duration of voltages (bits) and so on.
Name 6 protocols that operate at the application layer?
BGP, DHCP, DNS, FTP, HTTP, IMAP, IRC, LDAP, MGCP, NNTP, NTP, POP, RIP, RPC, RTP, SIP, SMTP, SNMP, SOCKS, SSH, TELNET, TLS/SSL, XMPP
Name three protocols that operate at Transport layer?
TCP, UDP, DCCP, SCTP, RSVP, ECN
Name 3 protocols that operate at the Internet Layer?
IP (IPv4, IPv6), ICMP, ICMPv6, IGMP, IPsec
Name 3 protocols that operate at the Link Layer?
ARP, InARP, NDP, OSPF, L2TP, PPP, Media Access Control, DSL, ISDN
What is TCP considered?
Reliable Connection
Name the Seven Layers of the OSI Model
Application, Presentation, Session, Transport, Network, Data-Link, Physical
What Layer do Switches operate at?
Layer 2
What Layer do Bridges operate at?
Layer 2
What is the most effective way to troubleshoot?
Layered approach, that is why it is critical to know the OSI model backwards and forwards.
What does HDLC stand for? What layer does it run at?
High Data Link Control - Layer 2
True or False - Does Layer 2 perform error recovery?
False - It does perform Error Detection through Frame check sequencing but does NOT perform error recovery
TRUE or FALSE - Is a MAC address part of the Physical Layer?
False - MAC addresses are layer 2
At the Application, Presentation and Session Layers, Data is called…
DATA
At the Transport layer, Data is placed into …..
SEGMENTS
At the Network layer Data is placed into…
PACKETS
At the Data Link layer, data is placed into….
FRAMES
At the Physical layer, data is….
BITS - Remember, it all comes down to 1’s and 0’s
Which Layers a header?
Application, Presentation, Session, Transport, Network, Data Link - all of them with the exception of the Physical Layer
What Layer adds a Header AND Trailer?
Data Link Layer - The first six layers of the OSI model add a layer specific header.
What is a PDU?
The combination of data and layer specific header is called a PDU (Protocol Data Unit) There is a PDU for each layer. (i.e the combination of data and L7 header information is called and L7 PDU)
True or False - After data is successfully transmitted by the physical layer to the remote location, the data travels back up the OSI model. Each layer removing the header added by its counterpart (i.e layer 3 removes the L3 header and reads it, etc)
True
What is Same-Layer Interaction Describe?
The process of a given OSI layer removingthe header placed on the data by the same layer on the sending side.
What is the name of another model, similar to OSI model?
TCP/IP Model
What are the layers of the TCP/IP Model?
Application - Transport - Internet - Network Access
What does the Application layer of the TCP/IP model handle?
All of the same items/tasks as the first three models of the OSI model, Application, Presentation, Session Layers.
What does the Transport Layer of the TCP/IP Layer handle?
The TCP/IP Transport layer maps directly to the Transport layer of the OSI model. TCP and UDP both operate at this layer and data takes the form of SEGEMENTS
What does the Internet layer of the TCP/IP layer handle?
The internet layer of the TCP/IP model maps the the Network layer of the OSI model. Both layers are responsible for routing through the use of IP addresses, static routes, and dynamic routing.
What does the Network Access Layer of the TCP/IP model do?
the Network Access Layer maps to the Data Link and Physical layers of the OSI model
What layer do you start trouble shooting at?
Physical layer - take a structured approach - Don’t look for the obscure solution, look for the obvious solutions first.
What type of connection is a TCP connection?
Reliable, connection orientated
What type of connection is a UDP connection?
Unreliable, Connectionless
What is a Three Way Handshake?
Before a sender can start sending there is going to be a negotiation between the two devices regarding rules for data transmission. 1. This begins with the sender transmitting a TCP segment with the Synchronization (SYN) bit set. 2. The recipient responds with a TCP segment with both the synchronization and acknowledgement bits set (SYN/ACK) 3. The sender responds with an ACK - The three way handshake is complete
True or False - UDP uses a Three Way Handshake
False
In addition to the orderly construction of the communication channel, TCP uses the ________ bit to bring the channel down when the communication is closed
FIN or Finish
What is the difference between Error Detection and Error Recovery?
Detection only finds the error and Recovery does something about it.
What does the ACK number indicate?
The next sequence number the data recipient expects to see. This is in place so the host knows that all segments sent have been received and which segment it is expecting next.
What does PAR stand for?
Positive Acknowledgement with Retransmission. Sender will set an acknowledgement timer, if ACK isn’t received by timer end, the sender will resend all segments again.
True or False - TCP does windowing
True
True or False - UDP does Windowing
False
What does the term “Sliding Window” refer to?
Dynamic adjustment of window size
What values do the TCP and UDP headers have in common?
Source port - Destination port - Checksum
What is the purpose for UDP?
Reduction in overhead - The TCP header is much larger thand the UDP header. that header is is being applied to every segment and that can add up. The advantage to UDP is that its header is much smaller than TCP
True or False - Ports allow for determination of what data consists of?
True
What is Multiplexing?
Multiplexing describes mixing of data streams. The use of port numbers to drive different data streams to the appropriate applications.
What is a Socket?
A Socket is a combination of IP address and Port number. (i.e. the socket on 10.1.1.2 for port 69 is 10.1.1.2:69) The socket can also be expressed with this format (IP address, Transport protocol, port number - 10.1.1.2,UDP,69)
What port number does FTP use?
TCP ports 20 and 21
What port does SSH use?
TCP port 22
What port does SMTP use?
TCP port 25
What port does HTTP use?
TCP port 80
What port does POP3 use?
TCP port 110
What port does SSL use?
TCP port 443
From the CL, what command gives a list of ports most commonly used?
access-list 100 permit TCP any any eq ?
What port does DHCP run on?
UDP ports 67 and 68
What port does TFTP use?
UDP port 69
What port does SNMP use?
UDP port 161
what Protocol uses both TCP and UDP ports?
DNS uses both UDP and TCP ports 53
What port is reserved for Private Mail systems?
The port number 24 is reserved in both UDP and TCP for private mail systems
What ports are reserved for VoIP (Voice Traffic)?
UDP ports 16,384 - 32,767
