Task 1.4 L2-Protocol Tunneling

Hello guys;

Dont you think there are other commands here needed to prevent multicast flooding through this metro connection .

My answer included this configuration along with the SG Answer.


int range fa0/13-14

switchport block multicast



int range fa0/16-17

switchport block multicast


  • I agreed with you that other commands are missing from SG.

    INE staff, can you please comment?

  • After a couple of years, still missing that commands.

  • Hello,

    Wouldnt this cause a loop? 

    I was expecting the SG to make an ether channel between SW1-SW2 on vlan 100,200.

    R4 sends a frame, SW4 places it on the wire of f0/16 and f0/17 since they are both on VLAN45 (frame is still untagged, native vlan)...each one of those receiving ports on the receiving side of SW2 adds the metro tag of 100 and 200 respectively on each port. Now the 1x frame R4 sent is now 2x frames that get trunked ower to SW1. Once they pass through SW1, the single frame that R4 sent is now 2x frames that are about to go out  of  both of SW1 ports connected to SW3. SW3 receives 2x frames and sends them both out to R5, since it is on VLAN45. 

    What happens with a regular unicast? R4 sends a packet and R5 gets it twice.

    What happens then if its a broadcast? LOOP!

    The initial configs that I have dont have a l2-protocol-tunnel point-to-point...(to make an etherchannel over q n q). 

    Does anyone else experience this?

  • In regards to plucena24's question - we still have STP on vlan 45 and we are bridging the BPDUs, so no loops could be formed:


    Rack1SW3#sh spanning-tree vlan 45

      Spanning tree enabled protocol ieee
      Root ID    Priority    32813
                 Address     0023.347c.c400
                 Cost        19
                 Port        15 (FastEthernet0/13)
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

      Bridge ID  Priority    32813  (priority 32768 sys-id-ext 45)
                 Address     0024.f9bd.3f80
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
                 Aging Time  300 sec

    Interface           Role Sts Cost      Prio.Nbr Type
    ------------------- ---- --- --------- -------- --------------------------------
    Fa0/5               Desg FWD 19        128.7    P2p
    Fa0/13              Root FWD 19        128.15   P2p
    Fa0/14              Altn BLK 19        128.16   P2p


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