Hubs and Switches – Study Outline

Chapter 2

22 – Comparing Unicast, Broadcast, and Multicast

23 – Unicast traffic: Transmitted from one computer to one other computer.

23 – Packets, Frames, PDU’s – Notes from class

24 – Broadcast traffic – Transmitted from one computer to every computer.

25 – Multicast traffic – Transmitted from one computer to many other computers.

26 – Understanding Network Hardware

  • Collision Domain: A collision domain is group of devices on the same segment that are subject to collisions. Collisions occur when two devices on the same segment send traffic at the same time. In other words, only one device can send data at any given time. If a collision occurs, both devices must then resend the data. Collisions are not good, and excessive collisions degrade the network performance.
  • Broadcast Domain: A broadcast domain is a group of devices on a network that can receive broadcast traffic from each other. In other words, if one device sends a broadcast packet, all other devices in the broadcast domain will receive it. Broadcasts are necessary, but it’s useful to limit the number of computers in a broadcast domain. Different devices are used to create separate collision domains and separate broadcast domains. Although the following sections cover many devices, it’s important to understand how switches and routers are related to collision and broadcast domains.
  • Switches: Switches connect computers in a network. Switches create separate collision domains. A switch passes broadcast traffic to all connections so it does not separate broadcast domains.
  • Routers: Routers connect networks. Routers do not pass broadcast traffic. Routers create both separate collision domains and separate broadcast domains.

27 – Understanding Hubs: Hubs provide basic connectivity for devices in a network. Although these were once common devices on Ethernet networks, switches have replaced them in most networks today. A hub doesn’t have any intelligence, and any data that is sent to one port is forwarded to all ports.

28 – Understanding Switches: Switches connect computers within a network similar to how hubs connect the computers. However, switches improve the performance of a network since they isolate the computers into separate collision domains.

Chapter 8

153 – Connecting Multiple Computers

  • network, subnets, and subnetworks

156 – Understanding Physical Ports

  • Switches have physical ports where physical cables plug in. For example, if the network is using twisted-pair cable, the switch will have RJ-45 ports that accept RJ-45 connectors. If the cable is fiber optic, the switch has physical ports that accept the fiber-optic connectors.
  • Identify port drawings (E, F, Gi)

158 – Comparing Hubs and Switches

  • A collision domain is a group of devices on the same segment that are subject to collisions.
  • A hub creates a single collision domain.
  • A switch creates multiple collision domains.

161 – Mapping Ports to Mac Address

  • Every network interface card (NIC) has a MAC address assigned to it. MAC addresses are typically burned into the card and unchangeable, though some NICs allow you to modify the MAC. Additionally, when a computer sends data to another computer, it always includes both its own IP address and its own MAC address as part of the source information.
  • A simple switch starts with very little knowledge when it’s turned on. It knows what ports it has, but it does not know which computers are connected to which ports. However, as traffic is sent through the switch, it learns. It populates an internal MAC address table with the MAC addresses of each computer and maps them to the port to which they’re connected.

162 – Comparing Managed / Unmanaged Switches

  • An unmanaged switch is just like a hub with respect to administrative overhead. There isn’t any. You take the switch out of the box and plug it in, and it works. The switch will monitor the traffic from each of the ports and build the MAC address table. As mentioned, the MAC address table maps the MAC addresses of the connected computers to their respective ports. Even though an unmanaged switch doesn’t require any administration, it does provide performance benefits over the simple hub. It still creates separate collision domains and increases performance on the network. Unmanaged switches operate at layer 2 of the OSI Model.
  • A managed switch can be configured. Managed switches are commonly managed using protocols such as Telnet or Secure Shell (SSH), and administrators can monitor and configure the switch remotely. As a reminder, SSH encrypts the traffic so that it can’t be read if intercepted by a protocol analyzer or sniffer, while Telnet transmits in clear text. Some of the management tasks that an administrator can perform are as follows:
    • Configure static entries in the MAC table.
    • Configure duplex settings (half-duplex or full-duplex) on ports.
    • Monitor performance of the switch using the Simple Network Management Protocol (SNMP).
    • Configure the switch to send alerts called traps with SNMP when certain events occur.
    • Create a virtual LAN (VLAN).
    • Configure port mirroring.
  • A layer 2 switch has the primary purpose of segmenting collision domains at layer 2 of the OSI Model. Each port is segmented from the others. Layer 2 switches are hardware based, which makes them extremely fast. They use the integrated circuitry on the main board (the hardware) to move data between ports at lightning speed.
  • A layer 3 switch operates at layer 3 of the OSI Model. It includes standard switching functionality, but also contains routing capability to route layer 3 traffic just as if it were a router. Although the router is a great layer 3 device, it can be slow, because additional processing of the packets must take place by the integrated software. A hardware-based switch is quicker.

164 – Create a VLAN

  • A virtual LAN (VLAN) is like a LAN inside a LAN. However, just as the name implies, it is created virtually, not with extra physical hardware. The benefits of creating a VLAN include the following:
    • Improved LAN security, because broadcast traffic is limited to specific ports.
    • The ability to group workstations or servers based on needs, not physical location.
    • Improved network performance for each separate broadcast domain.

167 – Exploring Switch Speeds

  • transmission
    • Switches are commonly represented with port speeds such as 10/100 Mbps or 100/1000 Mbps. The 10/100 means that a port may operate at either 10 Mbps or 100 Mbps, and the 100/1000 means that a port can operate at either 100 Mbps or 1000 Mbps.
    • The limiting factors are the capabilities of the end devices and the cable grade that is used. In other words, CAT 5 twisted-pair cable can’t be used for 1000 Mbps, though CAT 5E can.
    • Similarly, if a computer has a 10 Mbps NIC, the switch can send data to the NIC only at 10 Mbps no matter how fast the switch is.
    • High-speed switches are available. Of course, they are more expensive. If you have a group of users who need to share large files, stream audio and video, or use Voice over IP (VoIP), it’s worth getting the high-speed switches. If you do, you also need to ensure that the connecting cable and individual NICs meet the speed requirements.
    • If you are using a managed switch, you can manually configure individual ports for speed. Some ports could be set at 10 Mbps, some at 100 Mbps, and some at 1000 Mbps, as long as the switch supports all the speeds. Additionally, you can configure the ports individually for half-duplex or full-duplex.
    • Autosense for speed between the PC and the port is a common option with many switches. In other words, you don’t have to set the speed, but the switch automatically determines the best settings for optimal speed.
  • Uplinks connect two switches together or connect the switch to a router.
  • Backplane
    • Another speed to consider with switches is the backplane speed. The backplane speed is the internal speed of the switch. The faster this speed is, the better the overall performance of the switch.
    • Backplane speed applies only to modular switches, not form factor switches. It measures how fast data is transferred between modules in the switch.
    • Depending on the manufacturer, backplane speed may be measured at a couple different points. The first would be the speed on the chassis where the modules plug in. This is sometimes referred to as the speed between application-specific integrated circuits (ASICs), or the ASICs speed. This is similar in concept to the bus speed on a computer.
    • The second backplane speed measurement is between ports on the different blades on the same chassis. This is slightly different from the ASICs speed and is sometimes referred to as the port-to-port speed.
  • Uplink Port
    • An uplink port is a special port on a switch used to connect the switch to another switch or to another device. In contrast, other ports on the switch are called access links.
    • Uplink ports offer scalability by allowing you to add switches to the network in a daisy chain. You can also use the uplink port to connect the switch to a router for access to other subnets.

170 – Understanding Security Options

  • Port security helps you restrict what devices can connect to ports on a switch. The danger is that if someone can walk into your organization and simply plug a computer into an RJ-45 jack in the wall, they can access your network. That’s disconcerting to both administrators and organization executives.
  • Hardware redundancy simply means that additional components are added to ensure that the failure of one component doesn’t result in a complete failure.