Cisco Discovery Protocol

This Protocol is by default enabled in Cisco devices. It will send periodic update after every one minute on all interface. The neighbors will receive this information and store in the CDP neighborship table. CDP is helpful in troubleshooting or to create documentaion of CDP. We can obtain following information about neighbor automatically.

1.   Hostname
2. Device type
3. Model/Platform
4. IOS version 
5. Local connected interface
6. Entry IP address etc.

Display CDP status --> Router#sh cdp interface

To display CDP enabled interfaces --> Router#sh cdp interface 

To display CDP neighbors --> Router#sh cdp neighbor detail or Router#sh cdp nedighbor detail

To disable CDP from device

Router#conf ter

Router(config)#no cdp run

To disable CDP on particular interface
Router#conf ter

Router(config)#int <type> <no.>

Router(config-if)#no cdp enable

Router(cobfig-if)#exit

To change CDP timers
Router#conf ter
Router(config)#cdp timer <value> (by default 60 sec)

Router(config)#cdp holdtime <value> (by default 180 sec)

(Value in seconds) 

TCP/IP Model

TCP/IP is the most popular protocol stack, which consist of large no of protocol According to the OSI model TCP/IP consist of only four layers. TCP/IP model is modified form of DOD (Department of Defense) model. 

Application Layer
This layer contains a large no. of protocols. Each protocol is designed to act as server & client. Some of protocol will need connection oriented. TCP and others may need connection less UDP for data transfer. 
Application layer use port no.s to identity each application at Transport layer.  This layer performs most of functions, which are specified by the Application, Presentation, and Session layer of OSI model.

Transport Layer :- Two protocols are available on transport layer

1. Transmission Control Protocol
2. User Datagram Protocol

1> Transmission Control Protocol :- TCP performs connection-oriented communication. Its responsiblitis are :-

1. Error Checking
2. Acknowledgement
3. Sequencing
4. Flow Control
5. Windowing

2) User Datagram Protocol
UDP is connection less protocol, which is responsible for error checking and identifying applications using port numbers. 

UDP Header (8 bytes)       

                                            Source port  16 bits                         Destination port  16 bits  

                                                   Length  16 bits                                  Ckecksum  16 bits 

                                                                                      DATA

Internet Layer

The main function of Internet layer is routing and providing a single network interface to the upper layers protocols. Upper or lower protocols have not any functions relating to routing. To prevent this, IP provides one single network interface for the upper layer protocols. After that it is the job of IP and the various Network Access protocols to get along and work together. The main protocols are used in Internet layer :-

1. Internet Protocol (IP)
2. Internet Control Message Protocol ICMP)
3. Address Resolution Protocol (ARP)
4. Reverse Address Resolution Protocol (RARP)
5. Proxy ARP

Internet Protocol

This protocol works at internet layer. It is responsible for logical addressing, defining type of service & fragmentation.

Posted in: CCNA