Lab1.45 Flex links - Bridging & Switching

The solution guide is:

SW1#
interface Port-channel1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 switchport backup interface Fa0/16
 switchport backup interface Fa0/16 preemption mode bandwidth
 switchport backup interface Fa0/16 preemption delay 20

Although this solution meets the requirement in the given failure scenario (when we shut/unshut the port channel), it does not meet the last requirement in some other scenarios. More specifically, in scenarios where only one physical link is bounded to the channel group, the port-channel will not take the active role after a failure. For instance:

Shutdown the port channel on SW1, then we also shutdown one interface (e.g. fa0/14 of SW2). When we unshut interface port-channel 1, the port channel will come up, with only one active interface (fa0/13). The port-channel interface bandwidth is only 100Mbps, which is equal to that of interface Fa0/16. In this case, the ether channel interface will not preempt the currently active interface Fa0/16.

To meet the task requirement, we need to configure interface Port-channel1 with

SW1#
interface Port-channel1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 switchport backup interface Fa0/16
 switchport backup interface Fa0/16 preemption mode forced
 switchport backup interface Fa0/16 preemption delay 20

Comments

  • <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">





    Yes that's true.  If the port-channel as a whole does down, and then
    only one member comes back up, preemption will not occur since the
    bandwidth is equal.  I've reworded the last bulletpoint to read as
    follows:

    ·       
    If the EtherChannel and all its
    members comes
    back up traffic should forward back over this link after 20 seconds.



    In this case the bandwidth preemption mode does meet the requirements
    in all situations.



    Thanks,



    Brian McGahan, CCIE #8593 (R&S/SP/Security)

    [email protected]

     

    Internetwork Expert, Inc.

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    huan wrote:

    The solution guide is:

    SW1#

    interface Port-channel1

     switchport trunk encapsulation dot1q

     switchport mode trunk

     switchport backup interface Fa0/16

     switchport backup interface Fa0/16 preemption mode bandwidth

     switchport backup interface Fa0/16 preemption delay 20

    Although this solution meets the requirement in the given failure
    scenario (when we shut/unshut the port channel), it does not meet the
    last requirement in some other scenarios. More specifically, in
    scenarios where only one physical link is bounded to the channel
    group, the port-channel will not take the active role after a
    failure. For instance:

    Shutdown the port channel on SW1, then we also shutdown one
    interface (e.g. fa0/14 of SW2). When we unshut interface port-channel
    1, the port channel will come up, with only one active interface
    (fa0/13). The port-channel interface bandwidth is only 100Mbps, which
    is equal to that of interface Fa0/16. In this case, the ether channel
    interface will not preempt the currently active interface Fa0/16.

    To meet the task requirement, we need to configure interface
    Port-channel1 with

    SW1#

    interface Port-channel1

     switchport trunk encapsulation dot1q

     switchport mode trunk

     switchport backup interface Fa0/16

     switchport backup interface Fa0/16 preemption mode forced

     switchport backup interface Fa0/16 preemption delay 20







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  • awesome...i had that exact question...and solved

     

    thankyou!

  •  

    1 more question> how do these 2 commands relate?

     from Petrs "Understanding STP and RSTP " blog post 

     

    1>mac address-table move update <transmit|receive>

     

    2>switchport backup interface f0/XX mmu primary vlan <#>

      ?..whats the vlan for in the second command...and i thought for the "uplink fast like behavior...to move mac addresses from one port to another...wouldn't it always be transmit?  or would this cmd be also comfigured on all possible recepients(other end of the link)with the receive keyword?


     

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