Ccna ch01

Editor's Notes

• #4: The reason that networks were even created is so that we can easily share information and files. Before networks, we had to use floppy disks or other type of physical media to share files. Before Local Area Networks (LANs), we used mainframes from IBM, Honeywell, DEC, and others. The first LANs used coax connectivity but distance and amount of hosts that could be on a network were limited. On a basic network, hardware addresses (MAC addresses) are used to communicate between the hosts. Hosts communicate with a language referred to as binary code – which is 0’s and 1’s.
• #5: In an internetwork, hosts still use hardware addresses to communicate between each host on the LAN. However, in an internetwork, hosts use logical addresses (IP addresses) to communicate with hosts on a different LAN (other side of the router). Each connection into a router is a different logical network (broadcast domain).
• #6: Routing protocols are used to tell neighbor routers about networks that they are not directly connected to. The routers place these networks in their routing table (map of the internetwork) Examples of routing protocols are RIP, RIPv2, IGRP, EIGRP and OSPF. EIGRP is a Cisco proprietary routing protocol and is the preferred routing protocol for most networks. You only have Cisco routers in your internetwork, right? Once all the routers have converged (all have the same routing table), then a routed protocol (typically and hopefully just IP) can send packets through the internetwork. In smaller networks, you can create static routes instead of using a routing protocol. However, EIGRP works well in small and large networks, so why go through the hassle of static routes? (except for maybe a default route to the Internet).
• #28: <number> Half-duplex Ethernet is defined in the original 802.3 Ethernet and uses only one wire pair with a digital signal running in both directions on the wire. It also uses the CSMA/CD protocol to help prevent collisions and to permit retransmitting if a collision does occur. If a hub is attached to a switch, it must operate in half-duplex mode because the end stations must be able to detect collisions. Half-duplex Ethernet—typically 10BaseT—is only about 30 to 40 percent efficient as Cisco sees it, because a large 10BaseT network will usually only give you 3- to 4Mbps—at most. But full-duplex Ethernet uses two pairs of wires, instead of one wire pair like half duplex. And full duplex uses a point-to-point connection between the transmitter of the transmitting device and the receiver of the receiving device. This means that with full duplex data transfer, you get a faster data transfer compared to half-duplex. And because the transmitted data is sent on a different set of wires then the received data, no collisions will occur—sweet! Full-Duplex is collision free Half-Duplex is subject to collisions Full-Duplex provides higher throughput than Half-Duplex Ethernet of the same bandwidth Half-Duplex operates in a shared collision domain Full-Duplex operates in a private collision domain
• #41: <number> Two collision domains, two broadcast domains. A router breaks up both collision domains and broadcast domains and a hub breaks up no collision domains.
• #42: <number> One broadcast domain, seven collision domains are shown. By default, switches break up collision domains with each port, but are one broadcast domain by default.
• #43: <number> Only the hosts connected to the switch can transmit simultaneously without causing collisions. Four collision domains are shown, one broadcast domain. By default, switches break up collision domains with each port, but they are only one broadcast domain by default.