ccnp sw ch 10

  1. Which one of the following cmds enables the use of RSTP?

  2. On which standard is RSTP based?

  3. Which of the following is not a port state in RSTP?

  4. When a swich running RSTP receives an 802.1D BPDU, what happens?

  5. When does an RSTP switch consider a neighbor to be down?

  6. Which process is used during RSTP convergence?

  7. What causes RSTP to view a port as a point-to-point port?

  8. Which of the following events triggers a topology change with RSTP on a nonedge port?

  9. Which of the following is not a characteristic of MST?

  10. Which of the following standards defines the MST protocol?

  11. How many instances of STP are supported in the Cisco implementation of MST?

  12. What switch cmd can be used to change from PVST+ to MST?

  13. What are the 3 roles that standard STP - 802.1D ports can take on?
    • root port
    • designated port
    • blocking port

    note:  uplinkfast reserves a hidden alternate port rope for parallel paths to the root but is in blocking.
  14. RSTP root bridge election the same as with 802.1D.  After this step, what port roles can be assigned?
    Root port - port on sw that has best path cost to the root. same as 802.1D

    Designated port - port on network segment  that has best root path cost to the root. 

    Alternate port - port has alternate path to the root.  path is less desirable, ex: access-layer sw with 2 uplinks, one is root and #2 is alternate.

    Backup port - port that provides redundant (but less desirable) connection to segment where another sw port already connects.  Used as backup if segment port is lost.

    Note:  With RSTP, and port role can have any port state.
  15. RSTP defines port states only according to what a port does with incoming frames.  What are these 3 port states?
    Discarding - incoming frames are dropped.  combines 802.1D Disabled, Blocking and Listening. 

    Learning - incoming frames are dropped, but MAC addresses are learned

    Forwarding - Incoming frames are forwarded

    Note:  With RSTP, and port role can have any port state.
  16. What are the versions of BPDUs and which version is for what protocol?
    • Ver 0 - 802.1D  (STP)
    • ver 2 - 802.1w  (RSTP)

    Note:  ver 2 is backward compatible with ver 0.  If sw receives a ver 0 BPDU, then it reverts that port back to ver 0.
  17. what is the interval (time) that RSTP can notice a neighbor has left the topology?
    3 times the hello interval, or 6 seconds.

    note: 802.1D uses max age timer of 20 seconds.
  18. RSTP port types determine how a sw bases its forwarding decisions. 
    What are the three port types?
    Edge port - single host only.  PortFast designates this.  If a BPDU is ever received, port loses edge port status.

    Root port - port has best cost to root of STP instance. only one at a time per switch. if alt path is detected, these are ID'd as alternate and could be placed on forwarding if needed.

    Point to Point port - any port connected to another switch.  uses handshake with other sw for topology clarity.

    Note:  point to point types are determined by duplex mode.  Full duplex are PtP. 

    note: Half duplex ports revert to 802.1D standards
  19. What does RSTP use in large networks to ensure loop free topology?
    Syncronization - nonedge ports start in Discarding state.  Root port is elected after root bridge is elected. 

    Then other nonedge ports handshake with neighbor.  Each sassumes that it is the designated port.  Superior cost to root wins.

    sync causes sw to isolate itself by placing all nonedge ports in discarding while it handshakes with the sending switch.

    This sync moves in waves down the chain of switches.
  20. When does RSTP detect a topology change?
    when a non-edge port transitions to the Forwarding state. 

    When a topo change is detected, it sends a TC (topology change) message out all nonedge ports.  MAC addresses are flushed after 2*hello (4 secs) from CAM. address are then relearned.
  21. what cmd sets a port into edge port type?
    I  spanning-tree portfast

    Note:  by default, RSTP all full duplex ports are put into PtP type. to make a port PtP manually, use:

    I  spanning-tree link-type point-to-point
  22. What is the default STP on Catalyst switches?

    How do you change it to RSTP?

    how do you verify RSTP is now in use?
    PVST+ is default on catalyst switches.  PVST+ operates one instance of STP for each vlan using 802.1D rules.

    use cmd:

    G  spanning-tree mode rapid-pvst

    verify with:

    sh spanning-tree vlan 171
  23. Describe the differences between 802.1Q STP and PVST+
    802.1Q STP - only one instance of STP is in use for all VLANs.  Called CST (common spanning tree)  operates over the trunk's native vlan. 

    PVST+ - One instance of STP for each VLAN. 

    802.1Q  not enough,  PVST+  too much.
  24. What is the standard for MST?
    802.1s  Multiple Spanning Tree Protocol
  25. What must be configured for MST to work?
    Regions.  Regions on each switch must have the same attributes. 

    • Attributes: 
    • MST config name (32 char)
    • MST config rev num (0-65535)
    • MST instance to VLAN mapping tables (4096 entries)

    MST sw to sw comms don't send mapping tables.  Table is hashed and compared in the other sws. 
  26. MST was designed to operate with other types of STP.  To do this, What computes the loop free topology in the MST region?

    How does this "look" to other STP (like CST)?
    • MST ises IST (Internal Spanning-Tree). 
    • IST is locally significant to the MST region.  From the outside, (CST) the MST region looks like one single bridge. 
  27. Detail MST REGION configuration.
    • G  spanning-tree mode mst
    • G  spanning-tree mst config
    • M  name region1
    • M  revision 1
    • M  instance 1 vlan 2-4, 5
    • M  show pending
    • M  exit

    Note:  by default, all vlans are mapped to instance 0.

    • Attributes: 
    • MST config name (32 char)
    • MST config rev num (0-65535)
    • MST instance to VLAN mapping tables (4096 entries)
  28. detail mst STP config commands.
    seet root bridge macro:  spanning-tree mst 1 root <pri-sec> diameter <diameter>

    set bridge pri: spanning-tree mst 1 pri 1

    set port cost: spanning-tree mst 1 cost <value>

    set port priority: spanning-tree mst 1 port-priority <value>

    • set STP timers:
    • span-tree mst hello-time <secs>
    • span-tree mst forward-time <secs>
    • span-tree mst max-age <secs> 

    Note:  timers are applied to all mst instances.
Card Set
ccnp sw ch 10
ch 10