CCNA Data CenterEthernet Communication

Standards

WHAT IS A LAN?

LAN COMPONENTS» Computers • PC and Servers» Interconnections • NICs and Media» Network Devices • Switches and Routers» Protocols • Ethernet, IP, ARP, DHCP

LAN FUNCTIONS

» Provides access to data and applications» Enables sharing of resources including

I/O devices (cameras and printers)» Connectivity to the Internet and other

networks

ETHERNET FROM THE 70S!Year Activity

1973 Eithernet invented at Xerox

1982 DIX releases 10Mbps Ethernet (version 2)

1983 IEEE approves 802.3 (10Base-5)

1985 IEEE approves 802.3a (10Base-2)

1990 IEEE approves 802.3i (10Base-T)

1995 IEEE approves 802.3u (100Base-TX)

1998 IEEE approves 802.3z (1Gbps)

2002 IEEE approves 802.3ae (10Gbps)

2010 IEEE approves 802.3ba (40Gbps & 100Gbps)

ETHERNET LAN STANDARDS» LAN protocols map to both OSI physical and

data link layers for cabling and signaling» IEEE 802.3 standard further divides the data link

layer into two sub layers • Logical Link Control (LLC) - Independent

function between network layer above and MAC layer

below • MAC – manages physical media access (MAC addresses)

CSMA/CD IN ETHERNET» Ethernet LANs manage signals on a network by using

Carrier Sense Multiple Access with Collision Detection or (CSMA/CD).

» Stations (Multiple Access) on a network can access the network at any time, but before sending data, they must determine whether or not is is already in use.

» If the network is not in use the station can then transmit.

» If the network is in use, the CSMA/CD station waits.

» A collision can occur if 2 stations, listen and hear nothing, then transmit simultaneously. Collisions damage the transmissions.

» After the collision occurs, stations must then retransmit.

ETHERNET FRAME FORMATPreamb

leDestination MAC

ADD.

Source MAC ADD.

Type/Length

Payload Frame Check

Sequence

(FCS)88 6 6 2 46-1500 4

» Ethernet II frames use EtherType to identify the upper layer protocol» IEEE 802.3 frames • Uses Start of Frame delimiter (SOF) – stealing 1 byte from Preamble • Uses Length in header to specify the length of the data field • IEEE 802.3 frames stores protocol information in the LLC layer between Length and Payload using DSAP, SSAP, and LLC CTL

UNICAST, BROADCAST, MULTICAST

» 3 major types of network communications • Unicast • Frame from 1 host to another host • Broadcast • Frame from 1 host to all hosts • Multicast • Frames from 1 host to a specific group of

hosts

ETHERNET ADDRESSES

» MAC addresses are assigned to the NIC card and often referred to as burned-in address or BIA

» MAC address are 48 bits long • 24 bits of Organizational Unique Identifier

(OUI) • 24 bits of vendor-assigned end station

address» Cisco MAC - 00:25:B5:00:11:00