Chapter 10 - Analyzing Ethernet LAN Designs

What is the only device that does not forward broadcast frames?

A router

Summarize the four key points regarding hubs!

1. A hub acts as a multiport repeater, blindly regenerating and repeating any incoming electrical signals out all other ports, even ignoring CSMA/CD rules. 2. When two or more devices send at the same time, the hub's actions cause an electrical collision, making both signals corrupt. 3. The connected devices must take turns by using CSMA/CD logic, so the devices share the bandwidth. 4. Hubs create a physical star topology.

What are Layer-2 bridges?

1. Bridges sat between hubs and divided the network into multiple collision domains. 2. Bridges increase the capacity of the entire Ethernet, because each collision domain is basically a separate instance of CSMA/CD, so each collision domain can have one sender at a time.

What are three key points summarizing broadcast domains?

1. Broadcasts exist, so be ready to analyze a design to define each broadcast domain, that is, each set of devices whose broadcast reach the other devices in that domain. 2. VLAN's by definition are broadcast domains created through configuration. 3. Routers, because they do not forward LAN broadcast, create separate broadcast domains off their separate Ethernet interfaces.

Summarize the six key points regarding collision domains!

1. LAN switches place each separate interface into a separate collision domain. 2. LAN bridges, which use the same logic as switches, placed each interface into a separate collision domain. 3. Routers place each LAN interface into a separate collision domain. (The term collision domain does not apply to WAN interfaces). 4. LAN hubs do not place each interface into a separate collision domain. 5. A modern LAN, with all LAN switches and router, with full duplex on each link, would not have collisions at all. 6. In a modern LAN with all switches and routers, even though full duplex removes collisions, think of each Ethernet link as a separate collision domain when the need to troubleshoot arises.

What's the maximum segment length of a 10/100/1000BASE-T cable?

100 m (328 feet

What is the maximum segment length for single-mode fiber (1000BASE-LX)?

5 km (3.1 miles)

What's the maximum segment length for multimode fiber (1000BASE-SX/LX)?

550 m (1800 feet)

What layer on a two or three-tier design would a WLC reside on?

A WLC will reside at the Distribution layer, since it's a central device making forwarding decisions between different W(LAN)'s.

What's the purpose of a WLC and LWAP(P)?

A Wireless LAN Controller (WLC) is a central device for WAP management. Therefore, the LWAPP will act as a lightweight wireless device providing connections for end-users. This will forward data between end-users on your WLAN and to the WLC.

What's the difference between a bridge and a switch?

A bridge was merely the predecessor to a switch.

What is a broadcast domain?

A broadcast domain is a logical part of a network where all devices can receive broadcast frames.

What is a collision domain?

A collision domain is a set of devices (or more accurately put, NIC's) where if more than one send data at the same time, the frames will collide.

What is the difference between a hub and a switch?

A hub acts as a multiport repeater. This means that as it receives incoming electrical signals, it will immediately forward a regenerated signal out all other ports except the incoming (received) port. However, as more and more devices connect to it, it would not be able to efficiently manage the volume of traffic that passes through it. A switch provides a better alternative that can improve the performance by interpreting the electrical signal as a Ethernet frame, and looking at the source and destination MAC address to make forwarding decisions.

What is one key difference that separated hubs, switches, and routers?

A hub is one large collision domain. The reason being, any and all devices will receive a copy of traffic because it acts as a multiport repeater, and nothing more. A switch segments collisions domains per port. This is why a switch is more efficient for handling traffic, because it reduces the risk of collisions. A router on the other hand separates collision and broadcast domains, meaning if a broadcast (FFFF.FFFF.FFFF) frame is sent, only devices within that network (not already segmented by VLANs) will receive that traffic. If you want to talk to devices outside your subnet, or on a different network, you need a router.

What is a two-tier campus design, and what is it also most commonly referred to as?

A two-tier design, also known as a collapsed core is separated by the access layer and distribution layer (core intermingled). A two tier-design solves two major design needs: 1. Provides a place to connect end-user devices (the access layer, with access switches). 2. Connects the switches with a reasonable number of cables and switch ports by connecting all 40 access switches to two distribution switches.

What's a summary of the access, distribution, and core layer?

Access - Provides a connection point (access) for end-user devices. Does not forward frames between two other access switches under normal circumstances. Distribution - Provides an aggregation point for access switches, providing connectivity to the rest of the devices in the LAN, forwarding frames between switches, but not connecting directly to end-user devices. Core - Aggregates distribution switches in very large campus LANs, providing very high forwarding rates for the larger volume of traffic due to the size of the network.

What is an access switch?

Access switches connection directly to end-users, providing user device access to the LAN. Access switches normally send traffic to and from the end-user devices to which they are connected and sit at the edge of the LAN.

What technology does a hub use for collision detection?

Carrier Sense Multiple Access / Collision Detection (CSMA/CD)

What is a distribution switch?

Distribution switches provide a path through which the access switches can forward traffic to each other. By design, each of the access switches connect to at least one distribution switch, typically to two distribution switches for redundancy. The distribution switches provide the service of forward traffic to other parts of the LAN. Note that most designs use at least two uplinks to two different distribution switches for redundancy.

What was the first device to allow multiple devices to send at the same time?

Ethernet transparent bridges (or simply put, bridges)

True or False? A switch can forward traffic between two different VLAN's?

False. A VLAN is the equivalent of multiple router ports. The reason being, both separate broadcast domains. Therefore, taking into consideration a switches logic (which communicates between devices on the same subnet or VLAN), you instead need a router to forward packets between VLAN's.

What is a VLAN?

If you want to know what a VLAN is, you first should know what a LAN is. A LAN is a term that describes all devices that are in the same broadcast domain. A VLAN on the other hand is a logical method to segment network traffic, and create multiple broadcast domains.

What is the formula for calculating a full mesh network?

N (N - 1) / 2

What are the four most common topology terms?

Star - A design in which one central device connects to several others, so that if you drew the links out in all directions, the design would look like a star with light shining in all directions. Full mesh - For any set of network nodes, a design that connects a link between each and every pair of nodes. Partial mesh - For any set of network nodes, a design that connects a link between some pairs of nodes, but not all. In other words, a mesh that is not a full mesh. Hybrid - A design that combines topology design concepts into a larger (typically more complex) design.

What is the key difference between the access layer, and the distribution/core layer?

The access layer provides network connectivity to end-user devices, such as computers. The distribution layer is primarily responsible for forwarding traffic between different departments, or more accurately between different access layer switches. The core layer on the other hand is a high bandwidth, high speed highway for traffic that is often reserved between sites, buildings, etc. Additionally, from the core switches it will forward traffic to the WAN in case of needing to communicate between long distances over the Internet.

Where on a two or three-tier design would a LWAPP (WAP) reside?

The access layer, since it's providing access to end-users for Enterprise features, functions, or the Internet.

Why might it not be beneficial to have a full mesh network?

The primary reason why full mesh networks aren't more common is due to cost, and sheer resources. If you had for example 6 switches, and wanted to have a full mesh network, you would do the following: 6 (6 - 1) / 2 = 15 links (and 30 switch ports - two per link - one port per end) Now, how does this handle scaling? Well... not too well. If you had 2 distribution switches, and 40 access switches, you would do the following: 42 (42 - 1) /2 = 861 links (and 1722 switchports)

True or False? A hub and switch use the same physical star topology?

True The reason being, the hub or switch is a central device for forwarding traffic, and as you connect more devices it looks like a star from a top-down view.

True or False? A two-tier design is also known as a hybrid design?

True. A two-tier uses both a physical star topology at the access layer, and a partial mesh at the distribution layer.

If you want to create numerous broadcast domains, utilizing every port on a router is extremely inefficient. As a result, what configuration tool or concept can we use in place of this?

Virtual Local Area Networks (VLAN's)

Give a short description of what a WLC and LWAP(P) is.

WLC - Controls and manages all AP functions (for example, roaming, defining WLANs, authentication) LWAP(P) - Forwards data between the wired and wireless LAN, and specifically forwarding data through the WLC using a protocol like Control and Provisioning of Wireless Access Points (CAPWAP)

What's the purple of a three-tier campus design (core)?

Well, instead of partially meshing your distribution layer between multiple buildings on a campus (a single link from one switch to every other switch), you can save on switchports and cables by installing two core switches for redundancy sake.

Cisco uses three terms to describe the role of each switch in a campus design. What are they?

a. Access Layer b. Distribution Layer c. Core Layer

Which of the following devices would be in the same collision domain as PC1? a. PC2, which is separated from PC1 by an Ethernet hub b. PC3, which is separated from PC1 by a transparent bridge c. PC4, which is separated from PC1 by an Ethernet switch d. PC5, which is separated from PC1 by a router

a. PC2, which is separated from PC1 by an Ethernet hub.

Which of the following devices would be in the same broadcast domain as PC1? (Choose three answers.) a. PC2, which is separated from PC1 by an Ethernet hub. b. PC3, which is separated from PC1 by a transparent bridge. c. PC4, which is separated from PC1 by an Ethernet switch. d. PC5, which is separated from PC1 by a router.

a. PC2, which is separated from PC1 by an Ethernet hub. b. PC3, which is separated from PC1 by a transparent bridge. c. PC4, which is separated from PC1 by an Ethernet switch.

In a three-tier campus LAN design, which of the following are typically true of the topology design? (Choose two answers.) a. The design uses a partial mesh of links between access and distribution switches. b. The design uses a full mesh of links between access and distribution switches. c. The design uses a partial mesh of links between the distribution and core switches. d. The end user and server devices connect directly to distribution layer switches.

a. The design uses a partial mesh of links between access and distribution switches. c. The design uses a partial mesh of links between the distribution and core switches.

Which of the following Ethernet standards support a maximum cable length of longer than 100 meters? (Choose two answers.) a. 100BASE-T b. 1000BASE-SX c. 1000BASE-T d. 1000BASE-LX

b. 1000BASE-SX d. 1000BASE-LX

In a two-tier campus LAN design, which of the following are typically true of the topology design? (Choose two answers.) a. The design uses a full mesh of links between access and distribution switches. b. The design uses a partial mesh of links between access and distribution switches. c. The design uses a partial mesh of links between the distribution and core switches. d. The end user and server devices connect directly to access layer switches.

b. The design uses a partial mesh of links between access and distribution switches. d. The end user and server devices connect directly to access layer switches.

The term ___ LAN refers to the LAN created to support the devices in a building or in multiple buildings in somewhat close proximity to one another.

campus

Which one answer gives the strongest match between one part of a typical three-tier design with the idea behind the listed generic topology design term? a. The access layer looks like a partial mesh. b. The distribution layer looks like a full mesh. c. The distribution layer looks like a hybrid design. d. The access layer looks like a star design.

d. The access layer looks like a star design.