# Cisco Networking/CCENT/Ethernet LANs

This lesson covers Ethernet LANs.

## Objectives and Skills

Objectives and skills for the Ethernet LANs and Devices portion of Cisco CCENT certification include:
* Select the components required to meet a given network specification
* Identify the appropriate media, cables, ports, and connectors to connect Cisco network devices to other network devices and hosts in a LAN
* Determine the technology and media access control method for Ethernet networks

## Readings

* Wikipedia: Ethernet
* Wikipedia: Ethernet frame
* Wikipedia: Hierarchical internetworking model
* Cisco: Introduction to LAN Protocols
* Cisco: Ethernet Technologies

## Multimedia

* YouTube: Ethernet Standards - CompTIA Network+ N10-006 - 5.4
* YouTube: Collision Domains and Broadcast Domains - CompTIA Network+ N10-005: 1.4
* YouTube: Crossover and Straight Through Cables - CompTIA Network+ N10-005: 3.1
* YouTube: Media Distance and Speed Limitations - CompTIA Network+ N10-005: 3.1
* YouTube: MAC Address Formats - CompTIA Network+ N10-005: 1.3
* YouTube: Understanding Unicast, Multicast, and Broadcast - CompTIA Network+ N10-005: 1.3
* YouTube: Wireless Connections - CompTIA Network+ N10-006 - 2.7
* Cisco: Introduction to LAN Switches
* YouTube: Hubs, Switches, and Routers

## Activities

* Review TechRepublic: Five Free Apps for Diagramming Your Network. Examine your school, work, or home network and draw a network diagram that documents the network infrastructure. Include all networks, routers, switches, and access points in the building.
* For the network diagram above, identify the cable categories and data link technologies in use. Which links are copper, which are fiber, and which are wireless? Which categories of copper and which types of fiber are installed? Which protocols / bandwidth speeds are in use (100BASE-T, 1000BASE-T, 802.11a/b/g/n/ac, etc.)? Which links are half-duplex and which links are full duplex?
* Enhance the network diagram above by adding IP addresses and MAC addresses to all devices. How many collision domains are included? How many broadcast domains are included?

## Lesson Summary

* Ethernet networking devices include repeaters and hubs, bridges and switches, access points, and routers.
* Repeaters and hubs function at the physical layer, forwarding bits to all connected devices.
* Bridges and switches function at the data link layer, forwarding frames only to one or multiple devices that need to receive it.
* Access points function at the data link layer, acting as a bridge between wired and wireless networks.
* Routers function at the network layer, forwarding packets between computer networks.
* An Ethernet frame is preceded by a preamble and start frame delimiter (SFD), which are both part of the Ethernet packet at the physical layer. Each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame. The frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data.
* A collision domain is a section of a network connected by a shared medium or through repeaters where data packets can collide with one another when being sent. A collision occurs when more than one device attempts to send a packet on a network segment at the same time.
* A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer, either within the same network segment or bridged to other network segments.
* Bridges and switches separate collision domains.
* Routers separate broadcast domains.
* Access layer devices connect end-workstations and servers, and may or may not provide layer 3 switching services.
* Distribution layer devices connect, route, and filter access layer devices.
* Core layer devices provide high-speed, highly-redundant forwarding services to move packets between distribution-layer devices in different regions of the network.

## Key Terms
### 1000BASE-T

    A term describing various technologies for transmitting Ethernet frames over category 5 or better twisted pair cables at a rate of one gigabit per second,

### 100BASE-T

    A term describing any of several Fast Ethernet standards for transmitting Ethernet frames over category 5 or better twisted pair cables at a rate of 100 Mbit/s.

### 10BASE-T

    A term describing technologies for transmitting Ethernet frames of category 3 or better twisted pair cables at a rate of 10 Mbit/s.

### bridge

    A device that connects two network segments, typically by operating transparently and deciding on a packet-by-packet basis whether or not to forward from one network segment to the other.

### broadcast address

    A logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams.

### category 3 cable

    An unshielded twisted pair cable used in telephone wiring designed to reliably carry data up to 10 Mbit/s.

### category 5 cable

    A twisted pair cable for carrying signals with performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), and 1000BASE-T (Gigabit Ethernet).

### category 6 cable

    A cable standard provides performance of up to 250 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), 1000BASE-T/1000BASE-TX (Gigabit Ethernet), and 10GBASE-T (10-Gigabit Ethernet).

### crossover cable

    A type of Ethernet cable used to connect computing devices together directly, most often used to connect two devices of the same type, such as two computers or two switches to each other.

### carrier sense multiple access with collision detection (CSMA/CD)

    A media access control method in which a transmitting data station detects other signals while transmitting a frame, and stops transmitting that frame, transmits a jam signal, and then waits for a random time interval before trying to resend the frame.

### Ethernet

    A family of computer networking technologies for local area networks (LANs) and metropolitan area networks (MANs) commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3.

### Ethernet address

    See MAC address.

### Fast Ethernet

    See 100BASE-T.

### Frame Check Sequence

    A 32-bit cyclic redundancy check used to detect any in-transit corruption of data.

### full-duplex

    A system that allows communication in both directions simultaneously.

### Gigabit Ethernet

    See 1000BASE-T.

### half-duplex

    A system that provides communication in both directions, but only one direction at a time (not simultaneously).

### hub

    A device used to connect multiple Ethernet devices together at the physical layer and make them act as a single network segment.

### Institute of Electrical and Electronics Engineers (IEEE)

    The organization responsible for the standards defining the physical layer and data link layer's media access control (MAC) of wired Ethernet.

### media access control (MAC) address

    A unique identifier assigned to network interfaces for communications on the physical network segment.

### multicast address

    A logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be sent to a group of destination hosts simultaneously.

### network interface card (NIC)

    Also known as network interface controller, a computer hardware component that connects a computer to a computer network.

### organizationally unique identifier (OUI)

    A 24-bit number that uniquely identifies a vendor, manufacturer, or other organization globally or worldwide, and used as the first three octets of a MAC address.

### RJ-11 (Registered Jack-11)

    A 6 position 2, 4 or 6 contact modular connector typically used for phone cable connections

### RJ-45 (Registered Jack-45)

    An 8 position 8 contact modular connector typically used for network cable connections.

### repeater

    See hub.

### rollover cable

    A type of null-modem cable that is often used to connect a computer terminal to a router's console port.

### router

    A networking device that forwards data packets between computer networks.

### straight-through cable

    A type of Ethernet cable used to connect devices of different types together, such as a computer to a network switch or hub.

### switch

    A computer networking device that connects devices together on a computer network, by using packet switching to receive, process and forward data to one or multiple devices that need to receive it.

### unicast address

    A unique address identifying a single network destination for a transmission.

## Review Questions

* Ethernet networking devices include _____, _____, _____, and _____. Ethernet networking devices include repeaters and hubs, bridges and switches, access points, and routers.
* Repeaters and hubs function at the _____ layer, forwarding _____ to _____. Repeaters and hubs function at the physical layer, forwarding bits to all connected devices.
* Bridges and switches function at the _____ layer, forwarding _____ only to _____. Bridges and switches function at the data link layer, forwarding frames only to one or multiple devices that need to receive it.
* Access points function at the _____ layer, acting as a _____ between _____. Access points function at the data link layer, acting as a bridge between wired and wireless networks.
* Routers function at the _____ layer, forwarding _____ between _____. Routers function at the network layer, forwarding packets between computer networks.
* An Ethernet frame is preceded by _____, which are both part of the Ethernet packet at the _____ layer. An Ethernet frame is preceded by a preamble and start frame delimiter (SFD), which are both part of the Ethernet packet at the physical layer.
* Each Ethernet frame starts with _____, which contains _____ as its first two fields. Each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields.
* The middle section of an Ethernet frame is _____ including _____. The middle section of an Ethernet frame is payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame.
* The Ethernet frame ends with _____. The Ethernet frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data.
* A collision domain is _____. A collision domain is a section of a network connected by a shared medium or through repeaters where data packets can collide with one another when being sent. A collision occurs when more than one device attempts to send a packet on a network segment at the same time.
* A broadcast domain is _____. A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer, either within the same network segment or bridged to other network segments.
* Bridges and switches separate _____ domains. Bridges and switches separate collision domains.
* Routers separate _____ domains. Routers separate broadcast domains.
* Access layer devices connect _____, and may or may not provide _____. Access layer devices connect end-workstations and servers, and may or may not provide layer 3 switching services.
* Distribution layer devices connect, route, and filter _____. Distribution layer devices connect, route, and filter access layer devices.
* Core layer devices provide high-speed, highly-redundant forwarding services to move packets between _____. Core layer devices provide high-speed, highly-redundant forwarding services to move packets between distribution-layer devices in different regions of the network.

## Assessments

* Flashcards: Quizlet: CCENT - Ethernet LANs
* Quiz: Quizlet: CCENT - Ethernet LANs