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CCNA Guide to Cisco Networking Fundamentals Chapter 13 Advanced Switching Concepts

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  • 1.CCNA Guide to Cisco Networking FundamentalsChapter 13 Advanced Switching Concepts

2. 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 3. 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 networks 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 4. Spanning Tree Protocol (continued) CCNA Guide to Cisco Networking Fundamentals 5. Spanning Tree Protocol (continued)

  • STP uses theSpanning 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, aroot 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 6. Spanning Tree Protocol (continued)

  • Bridges use STP to transfer the information about each bridges MAC address and priority number
  • Bridge protocol data units (BPDU)orconfiguration 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 7. 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 8. 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 9. 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 10. 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 11. 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 12. 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 13. Spanning Tree Protocol (continued) CCNA Guide to Cisco Networking Fundamentals 14. 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 15. 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 thedefault VLAN)
    • By default, every port on a switch is in VLAN 1

CCNA Guide to Cisco Networking Fundamentals 16. 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 17. Virtual LANs (continued) CCNA Guide to Cisco Networking Fundamentals 18. Virtual LANs (continued) CCNA Guide to Cisco Networking Fundamentals 19. 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 20. 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 21. CCNA Guide to Cisco Networking Fundamentals 22. 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 23. 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 workstations MAC address

CCNA Guide to Cisco Networking Fundamentals 24. 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
  • TheIEEE 802.1qspecification that defines VLANs recommendsframe tagging
    • Also known asframe identification

CCNA Guide to Cisco Networking Fundamentals 25. 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 andInter-Switch Link (ISL) protocol

CCNA Guide to Cisco Networking Fundamentals 26. 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 27. 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 28. 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 29. 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 30. 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 31. 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 32. 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 33. VLAN Trunking Protocol (continued)

  • VTP pruningoption
    • 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 34. 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 35. Routers and VLANs

  • Routers can be used with VLANs to increase security
    • Must be used to manage traffic between different VLANs
  • Routers can implementaccess 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 36. CCNA Guide to Cisco Networking Fundamentals 37. Routers and VLANs (continued)

  • Router can either be an onboardRoute 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 38. 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 39. 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 40. 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 41. Summary (continued)

  • VLAN information is communicated to switches using the VLAN trunking protocol (VTP)

CCNA Guide to Cisco Networking Fundamentals