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CCNA Advanced Switching
 

CCNA Advanced Switching

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    CCNA Advanced Switching CCNA Advanced Switching Presentation Transcript

    • CCNA Guide to Cisco Networking Fundamentals Chapter 13 Advanced Switching Concepts
    • Objectives
      • Explain how the Spanning Tree Protocol works and describe its benefits
      • Describe the benefits of virtual LANs
      • Configure a VLAN
      • Understand the Purpose of the VLAN trunking protocol (VTP)
      • Configure VTP
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol
      • Physical path loops
        • A physical connection created when network devices are connected to one another by two or more physical media links
        • Help improve a network’s fault tolerance
      • Drawback
        • Can result in endless packet looping
      • Spanning Tree Protocol (SP)
        • A layer 2 link management protocol designed to prevent looping on bridges and switches
        • The specification for STP is IEEE 802.1d
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued) CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • STP uses the Spanning Tree Algorithm (STA)
        • To interrupt the logical loop created by a physical loop in a bridged/switched environment
        • STP does this by ensuring that certain ports on some of the bridges and switches do not forward frames
      • Building a logical path
        • Switches and bridges on a network use an election process to configure a single logical path
        • First, a root bridge ( root device ) is selected
        • Then, the other switches and bridges configure their ports, using the root bridge as a point of reference
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • Bridges use STP to transfer the information about each bridge’s MAC address and priority number
      • Bridge protocol data units (BPDU) or configuration bridge protocol data units (CBPDU)
        • The messages the devices send to one another
      • Each bridge or switch determines which of its own ports offers the best path to the root bridge
      • Root ports
        • The BPDU messages are sent between the root bridge and the best ports on the other devices
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • If BPDUs are not received for a certain period of time
        • The non-root-bridge devices will assume that the root bridge has failed, and a new root bridge will be elected
      • Once the root bridge is determined and the switches and bridges have calculated their paths to the root bridge
        • The logical loop is removed by one of the switches or bridges
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • Port states
        • STP will cause the ports on a switch or bridge to settle into a stable state
      • Stable states
        • The normal operating states of ports when the root bridge is available and all paths are functioning as expected
      • Transitory states
        • Prevent logical loops during a period of transition from one root bridge to another
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • The stable states are as follows:
        • Blocking
        • Forwarding
        • Disabled
      • The transitory states are as follows:
        • Listening
        • Learning
      • STP devices use the transitory states on ports while a new root bridge is being elected
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • Ports on STP-enabled devices move through the different states as indicated in the following list:
        • From bridge/switch bootup to blocking
        • From blocking to listening (or to disabled)
        • From listening to learning (or to disabled)
        • From learning to forwarding (or to disabled)
        • From forwarding to disabled
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • Topology changes
        • When the topology is changed, STP-enabled devices react automatically
        • If a device in an STP-enabled network stops receiving CBPDUs, then that device will claim to be the root bridge
          • Will begin sending CBPDUs describing itself as such
      • Per-VLAN STP (PVSTP)
        • Operates on VLANs and treats all VLANs connected as separate physical networks
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • Spanning Tree PortFast
        • Allows you to configure a switch to bypass some of the latency (delay)
          • Associated with the switch ports transitioning through all of the STP transitory states before they reach the forwarding state
      • Configuring STP
        • See Table 13-1
      CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued) CCNA Guide to Cisco Networking Fundamentals
    • Spanning Tree Protocol (continued)
      • Rapid STP (RSTP) 802.1w
        • Takes the basis of 802.1d (STP) and incorporates some additional features (such as portfast) that overcome some of the flaws of STP
      CCNA Guide to Cisco Networking Fundamentals
    • Virtual LANs
      • Virtual LAN (VLAN)
        • A grouping of network devices that is not restricted to a physical segment or switch
        • Can be configured on most switches to restructure broadcast domains
      • Broadcast domain
        • Group of network devices that will receive LAN broadcast traffic from each other
      • Management VLAN ( also known as the default VLAN)
        • By default, every port on a switch is in VLAN 1
      CCNA Guide to Cisco Networking Fundamentals
    • Virtual LANs (continued)
      • You can create multiple VLANs on a single switch
        • Or even create one VLAN across multiple switches
      • A VLAN is a layer 2 implementation, and does not affect layer 3 logical addressing
      CCNA Guide to Cisco Networking Fundamentals
    • Virtual LANs (continued) CCNA Guide to Cisco Networking Fundamentals
    • Virtual LANs (continued) CCNA Guide to Cisco Networking Fundamentals
    • Benefits of VLANs
      • Benefits:
        • Ease of adding and moving stations on the LAN
        • Ease of reconfiguring the LAN
        • Better traffic control
        • Increased security
      • VLANs help to reduce the cost of moving employees from one location to another
        • Many changes can be made at the switch
        • Physical moves do not necessitate the changing of IP addresses and subnets
      CCNA Guide to Cisco Networking Fundamentals
    • Benefits of VLANs (continued)
      • Because the administrator can set the size of the broadcast domain
        • The VLAN gives the administrator added control over network traffic
      • Dividing the broadcast domains into logical groups increases security
        • Requires a hacker to perform the difficult feat of tapping a network port and then figuring out the configuration of the LAN
      • VLANs can be configured by network administrators to allow membership only for certain devices
      CCNA Guide to Cisco Networking Fundamentals
    • CCNA Guide to Cisco Networking Fundamentals
    • Dynamic vs. Static VLANs
      • Static VLANs
        • Configured port-by-port, with each port being associated with a particular VLAN
        • The network administrator manually types in the mapping for each port and VLAN
      • Dynamic VLAN
        • Ports can automatically determine their VLAN configuration
        • Uses a software database of MAC address-to-VLAN mappings that is created manually
      CCNA Guide to Cisco Networking Fundamentals
    • Dynamic vs. Static VLANs (continued)
      • Dynamic VLAN could prove to be more time-consuming than the static VLAN
      • Dynamic VLAN allows the network administration team to keep the entire administrative database in one location
      • On a dynamic VLAN, moving a cable from one switch port to another is not a problem
        • Because the VLAN will automatically reconfigure its ports on the basis of the attached workstation’s MAC address
      CCNA Guide to Cisco Networking Fundamentals
    • VLAN Standardization
      • Before VLAN was an IEEE standard
        • Early implementations depended on the switch vendor and on a method known as frame filtering
      • Frame filtering
        • Complex process that involved one table for each VLAN
        • Had a master table that was shared by all VLANs
      • The IEEE 802.1q specification that defines VLANs recommends frame tagging
        • Also known as frame identification
      CCNA Guide to Cisco Networking Fundamentals
    • VLAN Standardization (continued)
      • Frame tagging
        • Involves adding a four-byte field to the actual Ethernet frame to identify the VLAN and other pertinent information
        • Makes it easier and more efficient to ship VLAN frames across network backbones
          • Switches on the other side of the backbone can simply read the frame instead of being required to refer back to a frame-filtering table
      • The two most common types of frame tagging (encapsulation) are 802.1q and Inter-Switch Link (ISL) protocol
      CCNA Guide to Cisco Networking Fundamentals
    • Creating VLANs
      • You can create VLANs by entering the (config-vlan)# mode and using the VLAN command
        • Or you can enter the VLAN database and use the VLAN configuration mode
      • To use the config-vlan mode, you type the following:
        • Rm410HL(config)#VLAN 2
        • Rm410HL(config-vlan)name production
      • To use the VLAN configuration mode, you start by entering the VLAN database
      CCNA Guide to Cisco Networking Fundamentals
    • Creating VLANs (continued)
      • The next step is to assign switch ports to the new VLANs
        • Ports can be assigned as static or dynamic
      • To remove a VLAN, use the no parameter:
        • Rm410HL(config)#no vlan 2
      CCNA Guide to Cisco Networking Fundamentals
    • Link Types and Configuration
      • Two types of links are on Cisco switches: trunk links and access links
      • Trunk links
        • Switch-to- switch or switch-to-router links that can carry traffic from multiple VLANs
      • Access links
        • Links to non-VLAN-aware devices such as hubs and individual workstations
      CCNA Guide to Cisco Networking Fundamentals
    • Link Types and Configuration (continued)
      • You choose from five different states for a trunk link:
        • Auto
        • Desirable
        • Nonegotiate
        • Off
        • On
      • To configure a trunk link on a Catalyst 2950, you must be in the appropriate interface configuration mode
      CCNA Guide to Cisco Networking Fundamentals
    • Link Types and Configuration (continued)
      • Switch interface descriptions
        • You can configure a name for each port on a switch
        • This is useful when you begin to define roles for a switch port on a more global basis
      CCNA Guide to Cisco Networking Fundamentals
    • VLAN Trunking Protocol
      • VLAN trunking protocol (VTP)
        • Created by Cisco to manage all of the configured VLANs that traverse trunks between switches
        • A layer 2 messaging protocol that manages all the changes to the VLANs across networks
      • VTP domains
        • VTP devices are organized into domains
        • Each switch can only be in one VTP domain at a time
          • All devices that need to share information must be in the same VTP domain
      CCNA Guide to Cisco Networking Fundamentals
    • VLAN Trunking Protocol (continued)
      • VTP device modes
        • Server
          • Device can add, rename, and delete VLANs and propagate those changes to the rest of the VTP devices
        • Client
          • Device is not allowed to make changes to the VLAN structure, but it can receive, interpret, and propagate changes made by a server
        • Transparent
          • A device is not participating in VTP communications, other than to forward that information through its configured trunk links
      CCNA Guide to Cisco Networking Fundamentals
    • VLAN Trunking Protocol (continued)
      • VTP pruning option
        • Reduces the number of VTP updates that traverse a link
        • Off by default on all switches
      • If you turn VTP pruning on
        • VTP message broadcasts are only sent through trunk links that must have the information
      • VLAN 1 is not eligible to be pruned because it is an administrative (and default) VLAN
      CCNA Guide to Cisco Networking Fundamentals
    • Nonswitching Hubs and VLANs
      • Important considerations:
        • If you insert a hub into a port on the switch and then connect several devices to the hub, all the systems attached to that hub will be in the same VLAN
        • If you must move a single workstation that is attached to a hub with several workstations, you will have to physically attach the device to another hub or switch port to change its VLAN assignment
        • The more hosts that are attached to individual switch ports, the greater the microsegmentation and flexibility the VLAN can offer
      CCNA Guide to Cisco Networking Fundamentals
    • Routers and VLANs
      • Routers can be used with VLANs to increase security
        • Must be used to manage traffic between different VLANs
      • Routers can implement access lists
        • Which increase inter-VLAN security
      • A router allows restrictions to be placed on station addresses, application types, and protocol types
      CCNA Guide to Cisco Networking Fundamentals
    • CCNA Guide to Cisco Networking Fundamentals
    • Routers and VLANs (continued)
      • Router can either be an onboard Route Switch Module (RSM) or an external router
      • The router will accept the frame tagged by the sending VLAN and determine the best path to the destination address
        • The router will then switch the packet to the appropriate interface and forward it to the destination address
      CCNA Guide to Cisco Networking Fundamentals
    • Routers and VLANs (continued)
      • Router-on-a-stick
        • If a single link is used to connect an external router with the switch containing multiple VLANs
          • Trunking is required for inter-VLAN routing
      • Trunking is the process of using either ISL or 802.1q to allow multiple VLAN traffic on the same link
        • For instance, an ISL trunk link would encapsulate each packet with the associated VLAN information and allow the router to route the packet accordingly
      CCNA Guide to Cisco Networking Fundamentals
    • Summary
      • The Spanning Tree Protocol (STP) allows administrators to create physical loops between bridges and switches
        • Without creating logical loops that would pose a problem for packet delivery
      • The Rapid Spanning Tree Protocol (RSTP) has enhanced STP to reduce the latency associated with convergence
      • Implementing VLANs via switches provides another way to increase the performance, flexibility, and security of a network
      CCNA Guide to Cisco Networking Fundamentals
    • Summary (continued)
      • VLANs are separate broadcast domains that are not limited by physical configurations
      • Performance benefits associated with VLANs are derived from limiting the amount of broadcast traffic that would naturally pass through a switch without filtration
      • Because traffic on a VLAN broadcast can be limited to a specific group of computers, security is also enhanced by making it more difficult for eavesdropping systems to learn the configuration of a network
      CCNA Guide to Cisco Networking Fundamentals
    • Summary (continued)
      • VLAN information is communicated to switches using the VLAN trunking protocol (VTP)
      CCNA Guide to Cisco Networking Fundamentals