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LLC (Logical Link Control) is basically the upper sublayer of the data link layer and ACTS as an interface between the network layer and MAC sublayer of the data link layer of the OSI MODEL. This sublayer provides the logic for data link as it CONTROLS the synchronization, flow control, multiplexing, and also error checking functions of the data link layer. It SIMPLY provides optional services to an application developer.

In TERMS of networking, the WINDOW is the NUMBER of segments that are allowed to be TRANSFERRED from the SOURCE to the destination before any acknowledgment is sent. 

User Mode: User mode is generally used to view the configurations of the routers. It allows US to view basic system information, check router status, connect to REMOTE devices, etc. User mode is mostly used to perform regular tasks on the router when we are using a CISCO router. 

Privileged Mode: Privileged mode is generally used to view all the configurations on the router. It allows you to change configurations that are LESS important. Privileged mode is mostly used to perform high-level tasks on the routers such as making configurations and DEBUGGING.

NETWORK latency basically represents the DELAY in communication over a network. It simply refers to the performance of one device when it communicates with ANOTHER. It is the time taken for some data to GO from the source to its DESTINATION across the network. Network latency can be affected by bandwidth speed, cabling, network card performance, and congestion. 

There are basically three different types of cables used in routing: 

Straight CABLE: These cables are used to connect different GROUP devices. It is especially used in LAN to connect different devices such as computers to a network hub like a ROUTER, PC and switch, router and switch, ETC. Its ultimate goal is to connect a host to the client.  

Cross Cable: These cables are used to connect the same group of devices. It is considered one of the most commonly used cable formats for network cables. It is especially used when two similar devices need to be connected. Cross cables are also known as cross-wired cables. 

Rollover Cable: These cables are used to connect the console port of the computer. This cable is specially designed flat to help distinguish it from other types of cables. It generally allows programmers to connect to network devices and can also manipulate the PROGRAMMING whenever needed. Rollover cables are also known as Yost cable, Cisco cable, or a Console cable.  

MTU (Maximum TRANSMISSION Unit) is considered the LARGEST size FRAME or packet that a network-connected device will accept.  Its default size is 1500 bytes which is the largest Ethernet standard unit. TCP (Transmission Control Protocol) GENERALLY uses MTU to determine the maximum size of each packet in any transmission. 

Three possible ways of data transmission in CCNA include: 

Simplex: The Communication is unidirectional in Simplex mode, as on a single-direction road. Just one of the two devices on a connection can communicate, the other can just get. The simplex mode can utilize the whole limit of the channel to send information one WAY.

Half Duplex: Each station can transmit and receive in Half-duplex mode, however not simultaneously. At the POINT when one device is sending, the other can just receive, and the other way around. The half-duplex mode is utilized in situations where there is no requirement for communication both ways simultaneously. The whole limit of the channel can be used for every direction.

Full Duplex: Both stations can send and receive all the while in full-duplex mode. Signals that are going in one direction share the CAPACITY of the connection with signals going another way IN this type of mode. This sharing can happen in two ways: 

• Either the connection should contain two truly separate transmission ways, one for sending and the other for receiving. 
• The capacity is split between signals going in two ways. 

Full-duplex mode is utilized when communication both ways are required CONSTANTLY. The limit or capacity of the channel, anyway, should be split between the two directions.

Frame relay is basically a packet switching technology typically USED to TRANSFER data between GEOGRAPHICALLY separated LANs or across WANs. It simply provides connection-oriented communication by developing and maintaining virtual circuits. It is cost-effective technology and is GENERALLY used to join TWO or more routers with a single interface. It works on the data link layer and physical layer of the OSI model.

The ROUTER command that is used to display RAM CONTENT is “SHOW run/show running-config", and the router command that is used to display NVRAM content is “Show start/show start-config".

DLCI (Data Link Connection IDENTIFIER) is BASICALLY a frame relay 10-bit-wide link-local VIRTUAL circuit normally assigned by frame relay SERVICE to uniquely identify each virtual circuit that is present on the network. It simply identifies which logical circuit the data travels over. 

HDLC (High-Level Data LINK Control) is a group of communication protocols that USUALLY provides reliable DELIVERY of data frames over communication or network link.  It is a PROPRIETARY protocol for CISCO and is the default encapsulation operated within CISCO routers. It ALSO ensures the error-free transmission of data and can provide both connection-oriented and connectionless services. 

Tracert: It is a Command Prompt command that is used to SHOW various details about the path that a packet takes from the source computer to the SPECIFIED destination computer. It only uses ICMP (Internet Control Message Protocol) echo REQUESTS. It can be used on a PC. This command is GENERALLY used in Windows NT-based OS. 

Traceroute: As the name suggests, it is a command that is used to trace the RECORDS of the path that a packet takes from the source computer to the specified destination computer. It uses UDP (User Datagram Protocol) echo requests. Traceroute command can be used on a router or switch. This command is generally used in UNIX OS.  

DIFFERENT memories that are used in CISCO router include: 

• NVRAM (Non-volatile RAM): It is used to store STARTUP configuration files. It also RETAINS its content even after a device is restarted or powered down.  
• DRAM (DYNAMIC Random-Access Memory): It is used to store configuration files that are being EXECUTED. It loses its content when a device is restarted.  
• ROM (Read Only Memory): It is used to store a bootstrap program that initializes a boot process. It also runs and maintains instructions for POST diagnostics. 
• Flash Memory: It is used to store CISCO IOS. It can also be used to store other files such as backup configuration files.  

STORE and forward SWITCHING method is MOSTLY used by CISCO Catalyst 5000 because it stores the entire FRAME to its buffers and executes a CRC check before deciding whether to forward that data frame or not.

100BaseFX is basically an Ethernet media standard for Ethernet over fiber OPTIC cables, rather than twisted-pair cables. It is a version of Fast Ethernet that makes USE of fiber optic cables as the main transmission medium. Here, 100 refers to 100Mbps DATA speed that means it carries data TRAFFIC at 100 Mbps in LAN.  

Data Link Layer: It is the 2nd layer of the OSI model which is generally responsible for transferring the datagram across an individual link. It is considered one of the most complicated layers and also has complex functionalities and liabilities. It also ENSURES that the appropriate physical PROTOCOL is assigned to the data. 

Transport Layer: It is the 4th layer of the OSI model which is responsible for providing transparent TRANSFER of data among end-users, thus providing RELIABLE data transfer SERVICES to the top layers. Its main objective is to deliver the entire message from source to destination. 

There are basically two different IPX access lists as GIVEN below: 

Standard: Used to filter the source or destination IP ADDRESS. 

Extended: USES source and destination IP ADDRESSES, protocol, socket, and port when fileting a network. 

The two ports of switches include: 

Access Port: It connects network hosts to a single VLAN and only CARRIES the traffic of one VLAN. In this, traffic is sent and received in native format WITHOUT any VLAN tagging.  Access ports are basically used to connect switch ports with computers with a minimum of 10 Mbps speed. 

Trunk Port: It generally connects to another switch and is able to INTERACT with several other VLANs. By DEFAULT, it is a MEMBER of all VLANs in the VLAN database. The trunk port is basically used for multiple connections between the switch to switch and switch to routers. 

Switching is a process in computer networks that enable us to interconnect LINKS to form a larger NETWORK. It works at the DLL frame and uses hardware address or mac address of DEVICES on LAN (Local AREA Network) to segment a network.

Types of routes available in ROUTERS INCLUDE:

Static Route: This route is also known as a non-adaptive route. It is either directly configured on an active interface of the router or manually added to the routing table by an administrator.

Default Route:  In this, the router is configured to send all packets towards a SINGLE router, and it does not matter whether or not it belongs to a specific network. It is especially used when networks deal with a single EXIT point. 
 
Dynamic Route: This route is also known as the adaptive route. It makes automatic adjustments of the routes as per the current state of the route in the routing table and also uses routing protocols to find network destinations.  

Router is a networking device that is used to forward data packets along with a network from source to destination. The DEVICES are specially designed to receive, analyze, and forward data packets between computer networks. It examines a destination IP address of a data packet and uses its headers and routing table to determine the best way or route for transferring the packets. There are some popular companies that develop routers like HP, Juniper, Nortel, Cisco, ETC. 

Functions of Routers:

• Send and receive data on computer networks. 
• Used to CREATE local networks of devices 
• Helps to connect multiple devices to the Internet. 
• Allows users to configure the port as per their requirements in the network. 
• Filter unwanted interference, and carry out the process of data encapsulation and decapsulation. 
• Used to segment network traffic. 
• Prevent network bottlenecks simply by isolating portions of a network. 
• Reduce EXCESSIVE traffic. 

Data packet is a unit of data that is MADE into a SINGLE package for transmission over a network. They are also referred to as a network layer package and are also used by IP protocol as they contain the IP information which is attached to each packet. They contain much essential information like email MESSAGES, website data, and VoIP (Voice-over-IP) calls. Each data packet has a unique numeric IDENTIFICATION number that DEFINES the packet number and order.  

Routing is basically a process of establishing the routes that data packets take on their way to the destination. It is a process of selecting a path across one or more networks to move a data PACKET from source to destination. Routing is generally performed in many types of networks such as circuit-switched networks, computer networks, ETC. It is considered as one of the most essential features in a network and is done by a DEVICE called routers.

In the above diagram, the data packet moves from Computer A to Computer B. There are two paths available: 

1st- Network 1, 3, and 5 
2nd- Network 2 and 4 

It depends upon network routers to make a choice WHETHER to pass through 1st or 2nd. The 1st one is a long path but might be faster at forwarding packets whereas the 2nd one is a shorter path. These are the kinds of choices that routers have to make constantly.