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Flashcards

Chapter 7: Spanning-Tree Configuration

Luis Domínguez CCNP SWITCH 300-115 300-115 Inglês 60 flashcards

Chapter 7: Spanning-Tree Configuration

Flashcards do conjunto (60)

  1. 1¿How we can activate an entire instance of STP?Switch(config)# spanning-tree vlan vlan-id
  2. 2¿How to activate STP for an specific Vlan or interface?Switch (config-if)# spanning-tree vlan vlan-id
  3. 3¿What can occur if STP bridge election is left to its default state?Poor choices like:
    1.- Slowest "root switch"
    2.- Backup "root switch" choice might not be the ideal switch or the ideal location.
    3.- Location of the "root switch" causing traffic from a large portion of the network to take a long and winding path just to pass through the root bridge
  4. 4¿What best practice we can do at the time to configure the Root Bridge election?■ Configure one switch as a root bridge in a determined fashion.
    ■ Configure another switch as a secondary root bridge, in case of a primary root bridge failure.
    ■ the root bridge (and the secondary) should be placed near the center of the Layer 2 network.
  5. 5STP bridge ID formats■ Traditional 802.1D bridge priority value (16 bits), followed by the unique switch MAC address for the VLAN
    ■ The 802.1t extended system ID (4-bit priority multiplier, plus a 12-bit VLAN ID), followed by a nonunique switch MAC address for the VLAN
  6. 6¿How is determined the use of STP BID formats?If the switch cannot support 1024 unique MAC addresses for its own use, the extended system ID is always enabled by default. Otherwise, the traditional method is enabled by default.
  7. 7¿How to begin to use the extended system ID method?Switch(config)# spanning-tree extend system-id
    you can use the traditional method by beginning the command with the NO keyword
  8. 8¿How to configure Catalyst switch to become the root bridge?■ Manually setting the bridge priority value
    Switch(config)# spanning-tree vlan vlan-list priority bridge-priority
    ■ Based on some assumptions about other switches in the network
    (root primary|secondary)
  9. 9Default BID values (Traditional 802.1D bridge priority value)32,768
  10. 10Range of BID values (Traditional 802.1D bridge priority value)0 to 65,535
  11. 11Range of BID values If 'extended system ID' is enabled- default 32,768 plus the VLAN number
    - from 0 to 61,440, but only as multiples of 4096 plus the VLAN number
  12. 12Command to configure 'Root Bridge' based on some assumptions of another sw in the networkSwitch(config)# spanning-tree vlan vlan-id root { primary | secondary } [ diameter diameter ]
  13. 13STP priority 0- automatic method will not use it
    - manually configure the priority to 0
    Switch(config)# spanning-tree vlan 100 priority 0
    - Ensure Root Switch election
  14. 14Sequence of four criteria that STP uses to choose a path1. Lowest bridge ID
    2. Lowest root path cost
    3. Lowest sender bridge ID
    4. Lowest sender port ID
  15. 15¿How is added the value "RPC" to the BPDU?As a switch receives a BPDU, the port cost of the receiving port is added to the root path cost in the BPDU
  16. 16Command to set a switch port’s path costSwitch (config-if)# spanning-tree [ vlan vlan-id ] cost cost
    **If the vlan parameter is given, the port cost is modified only for the specified VLAN. Otherwise, the cost is modified for the port as a whole (all active VLANs).
  17. 17¿How we can see the port cost of an interface?Switch# show spanning-tree interface type member/module/number [ cost ]
  18. 18The port ID value-16-bit quantity: 8 bits for the port priority, and 8 bits for the port number.
    - The port priority is a value from 0 to 255 & defaults to 128 for all ports
    - The port number can range from 0 to 255 & represents the port’s actual physical mapping
  19. 19How to configure the port prioritySwitch(config-if)# spanning-tree [ vlan vlan-list ] port-priority port-priority
    ** If vlan-id is not use the port priority is set for all the port as a whole. 128. A
    lower port priority value indicates a more preferred path toward the root bridge.
  20. 20Tuning Spanning-Tree Convergence- STP uses several timers, a sequence of states that ports must move through
    - In certain situations, the default STP can cause network access to be delayed while timers expire and while preventing loops on links where loops are not possible
  21. 21¿Where must you configure the timers?The timers need to be modified only on the root bridge because the root bridge propagates all three timer values throughout the network as fields in the configuration BPDU
  22. 22Manually Configuring STP Timers(config)# spanning-tree [ vlan vlan-id ] hello-time seconds
    (config)# spanning-tree [ vlan vlan-id ] forward-time seconds
    (config)# spanning-tree [vlan vlan-id ] max-age seconds
    ** If you omit the vlan keyword, the timer values are configured for all instances
  23. 23Hello timer (value of 1 to 10 seconds)- triggers periodic configuration BPDU messages that are sent from the root to other bridges in the network
    - This timer also sets the
    interval in which a bridge expects to hear a hello relayed from its neighboring bridges
    Switch(config)# spanning-tree hello-time 1
  24. 24Forward Delay timer- The default value is 15 seconds, but this can be set to a value of 4 to 30 seconds
    - This timer should be modified only under careful consideration because the value depends on the diameter of the network and the propagation of BPDUs across all switches
  25. 25Max Age timer- Specifies a stored BPDU’s lifetime that has been received from a neighboring switch with a designated port
    - The timer value defaults to 20 seconds but can be set from 6 to 40 seconds
  26. 26Automatically Configuring STP Timers- Modifying STP timers can be tricky
    - Default values and the calculations needed to derive proper STP operation
    - Timer values are basically dependent on the Hello Time and the switched network’s diameter, in terms of switch hops
  27. 27Catalyst switches offer a single command that can change the timer values in a more controlled fashionSwitch(config)# spanning-tree vlan vlan-list root { primary | secondary } [ diameter
    diameter [ hello-time hello-time ]]
  28. 28¿What is the DIAMETER option?The maximum number of switches that traffic will traverse across a Layer 2 network
  29. 29¿What does the previous command with the diameter option? *(per-Vlan basis)*STP timers will be adjusted according to the formulas specified in the 802.1D standard by giving only the network’s diameter and an optional hello-time . If you do not specify a hello time, the default value of 2 seconds is assumed.
  30. 30Network diameter range & default valur- Value from 1 to 7 switch hops
    - Default value of 7
  31. 31¿Whats is the command results?Because this command makes a switch become the root bridge, all the modified timer values resulting from this command will be propagated to other switches through the configuration BPDU
  32. 32Example of a network with 3 swtichesWe can assume the can quantity of 3 sws therefore the diameter option will be 3 and no the default option of 7 plus we can reduce the amount of the hello time by 1 to shorten the time needed to detect a dead neighbor.
    sw(config)# spanning-tree vlan 100 root primary diameter 3 hello-time 1
    This command will become the sw to be the Root and propagate the new timers
  33. 33Default timers Hello Time 2 sec Max Age 20 sec Forward Delay 15 secNew timers
    Hello Time 1 sec Max Age 7 sec Forward Delay 5 sec
  34. 34PortFastEnables fast connectivity to be established on access layer switch ports to workstations that are booting
  35. 35UplinkFastEnables fast-uplink failover on an access layer switch when dual uplinks are connected into the distribution layer
  36. 36BackboneFastEnables fast convergence in the network backbone or core layer switches after a spanning-tree topology change occurs
  37. 37command to enable PortFast as the defaultSwitch(config)# spanning-tree portfast default
  38. 38PortFast feature on specific switch portsSwitch(config-if)# [ no ] spanning-tree portfast
  39. 39What is the macro configuration command to force a switch port to support a single host?Switch(config)# interface G0/0
    Switch(config-if)# switchport host
    • switchport mode will be set to access
    • spanning-tree portfast will be enabled
    • channel group will be disabled
  40. 40Display current PortFast statusSwitch# show spanning-tree interface gigabitethernet 1/0/10 portfast
    • VLAN0010 enabled
  41. 41How to enable the UplinkFast feature?Switch(config)# spanning-tree uplinkfast [max-update-rate pkts-per-second ]
    *When UplinkFast is enabled, it is enabled for the entire switch and all VLANs
    *is not allowed on the root bridge switch .
  42. 42What about the modifications that are make by UplinkFast?UplinkFast makes some modifications to the local switch to ensure that it does not become the root bridge and that the switch is not used as a transit switch to get to the root bridge.
    *the goal is to keep UplinkFast limited to LEAF-NODE switches.
  43. 43What modifications are make by UplinkFast to ensure the leaf-node position of the switch?• Switch’s bridge priority is raised to 49,152
    • The port cost of all local switch ports is incremented by 3000
  44. 44What is the mechanism to notify other upstream switches that stations downstream can be reached over the newly activated uplink?• The switch accomplishes this by sending dummy multicast frames to destination 0100.0ccd.cdcd on behalf of the stations contained in its CAM table.
    • The MAC add are used as the SRC ADD in the DUMMY FRAME as if the stations actually had sent them
  45. 45max-update-rate parameter• Parameter that set the max bit rate in packets per second for the DUMMY FRAMES
    • default is 150 pps, range from 0 to 65,535 pps. If the value is 0, no dummy multicasts are sent
  46. 46command to display the current status of STP UplinkFastSwitch# show spanning-tree uplinkfast
    • UplinkFast is enabled
    • Station update rate set to 150 packets/sec.
  47. 47How works BackboneFast?BackboneFast works by having a switch actively determine whether alternative
    paths exist to the root bridge. in case the switch detects an INDIRECT LINK FAILURE
  48. 48Indirect Link FailureOccur when a link that is not directly connected to a switch fails and receives inferior BPDUs from its designated bridge on either its root port or a blocked port.
  49. 49Inferior BPDUsInferior BPDUs are sent from a designated bridge that has lost its connection to the root bridge, making it announce itself as the new root.
  50. 50How acts a switch when receive a inferior BPDU?• Normally, a switch must wait for the Max Age timer to expire before responding to the inferior BPDUs
    • BackboneFast begins to determine whether other alternative paths to the root bridge exist according to the following port types that received the inferior BPDU
  51. 51If the inferior BPDU arrives on a port in the Blocking stateThe switch considers the root port and all other blocked ports to be alternative paths to the root bridge
  52. 52If the inferior BPDU arrives on the root port itselfThe switch considers all blocked ports to be alternative paths to the root bridge.
  53. 53If the inferior BPDU arrives on the root port and no ports are blocked• The switch assumes that it has lost connectivity with the root bridge.
    • In this case, the switch assumes that it has become the root bridge, and BackboneFast allows it to do so before the Max Age timer expires.
  54. 54How BackboneFast detect an alternative path to the root bridge?If the local switch has blocked ports, BackboneFast use Root Link Query (RLQ) protocol to determine if upstream switches have connection to the RB
  55. 55How Root Link Query (RLQ) works?1.- RLQ Requests are sent out
    2.- If a switch receives an RLQ Request and either is the root bridge or has lost connection to the root, it sends an RLQ Reply
    3.- Otherwise, the RLQ Request is propagated on to other switches until an RLQ Reply can be generated
  56. 56How Root Link Query (RLQ) works? Part II4.- On the local switch, if an RLQ Reply is received on its current root port, the path to the root bridge is intact and stable
    5.- If it is received on a nonroot port, an alternative root path must be chosen.
    The Max Age timer immediately is expired so that a new root port can be found.
  57. 57How operates BackboneFast?1.- Shortens the time a switch waits to detect a root path failure (Max Age timer)
    2.- Ports still must go through Forward Delay timer intervals during the Listening and Learning states
    3.- BackboneFast can reduce the maximum convergence delay only from 50 to 30 seconds.
  58. 58Configuration BackboneFastSwitch(config)# spanning-tree backbonefast
    * BackboneFast should be enabled on all switches in the network (to enable RLQ Request and Reply mechanism)
    * By default, BackboneFast is disabled
  59. 59verify the current BackboneFast stateSwitch# show spanning-tree backbonefast
    BackboneFast is enabled
  60. 60Monitoring STPMonitoring STP

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300-115 CCNP SWITCH 300-115 (Part III: Working with Redundant Links) FlashCards sobre Chapter 7: Spanning-Tree Configuration, criado por Luis Domínguez em 05-04-2018.
Criado por
Luis Domínguez
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