ICND1 – OSI Model
Note: If you are not sure about OSI Model, please read my OSI Model Tutorial.
CDP runs at Layer 2 (Data Link) of the OSI model -> E is correct.
SMTP stands for Simple Mail Transfer Protocol. It’s a set of communication guidelines that allow software to transmit email over the Internet while File Transfer Protocol (FTP) is a standard network protocol used to transfer files from one host to another host over TCP-based network.
Note: Simple Network Management Protocol (SNMP) uses UDP as the transport protocol for passing data between managers and agents. SNMP uses UDP to help reduce the impact on your network’s performance. Although SNMP can be configured to run on TCP but we should only do it in special situations. SNMP uses the UDP port 161 for sending and receiving requests, and port 162 for receiving traps from managed devices.
DNS work on both the TCP and UDP protocols. DNS uses TCP for zone exchanges between servers and UDP when a client is trying to
resolve a hostname to an IP address. Therefore in most cases we say “DNS uses UDP”.
The primary function of an access-layer is to provide network access to the end user.
The hardware and software attributes of the access layer that support high availability include security services for additional security against unauthorized access to the network through the use of tools such as 802.1x, port security, DHCP snooping, Dynamic ARP Inspection, and IP Source Guard.
The picture below compares the two TCP/IP and OSI models:
Transmission Control Protocol (TCP) has all the features mentioned above and TCP resides in Transport Layer (Layer 4) of the OSI model.
Flow control: A methodology used to ensure that receiving units are not overwhelmed with data from sending devices when buffers at a receiving unit are full, a message is transmitted to the sending unit to temporarily halt trans-missions until all the data in the receiving buffer has been processed and the buffer is again ready for action.
Sequencing: is used to number segments before sending so they can be put back together again in the correct order at the receiving side.
Acknowledgment: When the receiver gets the data, it sends a response telling the sender that the data have been safely arrived.
In CCNA, the popular devices operate in Layer 1 are hub and repeater.