Del Mar College ITNW-Beginning Router Configuration Instructor: Michael P. Harris
Sem2Les2

Semester 2 Lesson 2 Notes:

The Medaia Layers: Ethernet and TCP/IP

1. Compare and contrast five different Ethernet Lan devices.

In increasing order of complexity (and typically cost):

1. "Repeaters" -- amplify and retime signals, layer 1 devices
2. "Hubs" -- concentrate signals but typically act as collision domains, layer 1 devices
3. "Bridges" -- allow segmentation of networks based on layer 2 address information, help filter LAN traffic based on MAC addresses
4. "Ethernet Switches" -- allow concentration of signals with shared bandwidth, layer 2 and 3 devices
5. "Routers" -- allow packet forwarding and best path selection, layer 3 (logical address) devices, perform path selection based on logical addresses

2A. Name two ways in which WANs differ from LANs.

WANs operate over a large geographical area (LANs do not);

WANs emphasize access over serial interfaces operating at lower speeds to ensure reliability (LANs can operate reliably at very high speeds with multiple access).

2B. Compare and contrast Ethernet, Token-Ring, and FDDI:

"Ethernet"

-- The first of the major LAN technologies, it runs the largest numbers of LANs. It is opportunistic, and typically uses UTP or coaxial copper cable.

"Token Ring"

-- From IBM, it followed Ethernet and is not widely used in a large number of IBM networks. It is deterministic, depending on token passing for access to the shared, typically copper media.

"FDDI"

-- Also a deterministic, token passing network technology based on optical fiber media. It is now a popular campus LAN media because of its high bandwidth and electrically insulating properties.

3. Expalin in detail how Ethernet/802.3 achieves reliable data communications with CSMA/CD?

"CSMA/CD" stands for carrier sense multiple access collision detect. When a station (node, host) wishes to transmit, it checks the shared network medium to determine whether another station is currently transmitting (it 'listens'). If the network is not being used, it begins transmitting. If two stations begin transmitting at the same time, a "collision" occurs -- but since the transmitting nodes continue to "listen" for collisions, they transmit a jam signal whenever a collision is detected. Then all transmitting stations backoff for a randomly selected amount of time before attempting to retransmit. This process is called "opportunistic", since no given station is automatically guaranteed the right to transmit at any given time.

4. Compare and contrast physical and logical addressing schemes.

"Physical addresses" are also called link layer or MAC addresses. Since they are unique for each network connection and follow no pattern other than being numbered sequentially on NIC cards, they are considered a 'flat addressing scheme'. They are analogous to social security numbers. "Logical addresses" are also called 'network or IP addresses'. They are assigned according to very structured rules and are a 'hierarchical addressing scheme'. They are analogous to the area code/exchange/extention system used in the US phone system or the name/address/city/state/zip code system used by the US postal service.

5. Given an IP host address of 192.168.5.121 and a Subnet mask of 255.255.255.248, find the subnet number on which this host is located -- explain all the steps of your work.

Answer: 192.168.5.120

(1) Write out both the IP address and the subnet mask in terms of bits.

192.168.005.121   11000000 10101000 00000101 01111001

255.255.255.248   11111111 11111111 11111111 11111000

(2) Then logically write the IP address with the subnet mask, bit by bit.

11000000 10101000 00000101 01111000

Rewrite the resulting binary number back as a decimal number. 192.168.5.120

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Lesson 1

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