spanning tree procedure

hi all, well i know how spanning tree works but when i use INE workbook then i feel something is missing in my knowledge .......

actually i have 4 switches which are connected simultaneously like SW1----SW2----SW3-----SW4----SW1 with all three multiple links

suppose SW1 is root bridge and sw4 is secondary root bridge now how SW2, SW3 and SW4 elect its port for designated and blocking state when there is three multiple link available between all connected switches.

Comments

  • Hello ssfouzdar.ie.

    Can you go through this pages?

    http://ieoc.com/forums/t/16429.aspx
    http://ieoc.com/forums/t/16384.aspx

    More ppls explained with good example. There you can find almost INE's switch topology with good explanation.

    HAPPY STUDY

    [:D]

     

     

    hi all, well i know how spanning tree works but when i use INE workbook then i feel something is missing in my knowledge .......

    actually i have 4 switches which are connected simultaneously like SW1----SW2----SW3-----SW4----SW1 with all three multiple links

    suppose SW1 is root bridge and sw4 is secondary root bridge now how SW2, SW3 and SW4 elect its port for designated and blocking state when there is three multiple link available between all connected switches.

     

  • Hi Shiv Fouzdar,

    1. For each LAN segment there will be only one DP to the Root Bridge, which has the lowest cost to the root.

    2. If the cost ties, then choose the one with lowest bridge priority.

    3. If bridge priority is same, then choose the one with lowest port priority

    4. If port priority ties, then choose the one with the lowest port ID.

    In your scenario, assuming all link has equal cost and default port priority, then:

    1. SW2 & SW4 will has its root port that connect to SW1's lowest port ID, the rest of the ports that connect to SW1 will be in blocking state.

    2. SW3 will has its root port that connect to lowest port ID of SW4 (SW4 is secondary RB). And has the rest of its ports that connect to SW4 will be in blocking state. Pls note for SW3 to reach SW1, it can go via SW2 and SW4 with the same cost, but SW4 is chosen bcoz of SW4's Bridge Priority.

    3. SW3 will has all of its ports connected to SW2 in blocking state.

    4. The rest are DP ports in forwarding state.

    You can watch excellent VoD by Brian McGahan about this topic in INE's ATC.

     

  • hi all, i know the procedure but my question is:- when all 4 switches with multiple connections are connected as round-robin like SW3---SW1---SW2----SW4----SW3 

    now SW1 is root bridge then how SW3 elect its port as compared with SW1 and then like wise all??

    well in my openion-

    SW3 will compare root cost first if it ties then move to port priority if it also ties then move to port id.

    actually SW3 is having fa0/13,14,15 connected with SW1 and SW3 of fa0/19,20,21 connected with SW4 of fa0/19,20,21 so SW3 will use only fa0/13,14,15 for selection after that it will compare all criteria with again fa0/19,20,21 to reach SW1 via SW4 so is this right procedure?

  • Hi Shiv,

    SW3 will select one port as the root port, which is the port that receives BPDU with the least cost to the root bridge. Assuming that all port cost are the same, then in this scenario it will pick one port from either F0/13, 14, or 15. If you follow INE topology, then port F0/13 of SW3 will be the root port as it is connected to SW1's port F0/16 (lowest port ID). Again, assuming port priority are all the same.

    Do we agree up to this point?

  • in same scenario,

    SW3-fa0/13,14,15-------fa0/16,17,18-SW1-fa0/13,14,15----------fa0/13,14,15-SW2-fa0/19,20,21--------fa0/16,17,18-SW4-fa0/16,17,18-----fa0/16,17,18-SW3

     

    on SW1#sh span vlan 1

    VLAN001      

    spanning tree enable protocol ieee

    Root bridge           SW1

    Bridge ID         priority   32769         mac add  001b.d490.7c00

    interface          role   state   cost        prio.nbr   type

    Fa0/13            Desg   FWD     19         128.15    p2p

    Fa0/14            Desg   FWD     19         128.16    p2p   

    Fa0/15            Desg   FWD     19         128.17    p2p

    Fa0/16            Desg   FWD     19         128.18    p2p

    Fa0/17            Desg   FWD     19         128.19    p2p

    Fa0/18            Desg   FWD     19         128.20    p2p 

     

     

    on SW2#show spanning vlan 1

    VLAN001

    spanning tree enable protocol ieee

    root bridge          SW1

    bridge id        priority        32769   mac add  001b.d490.7c00

    interface          role   state   cost        prio.nbr   type

    Fa0/13            root   FWD     19         128.15    p2p

    Fa0/14            ALTN   BLK     19         128.16    p2p   

    Fa0/15            ALTN   BLK     19         128.17    p2p

    Fa0/19            Desg   FWD     19         128.21    p2p

    Fa0/20            Desg   FWD     19         128.22    p2p

    Fa0/21            Desg   FWD     19         128.23    p2p

     

    on SW3#sh span vlan 1

    VLAN001      

    spanning tree enable protocol ieee

    Root bridge           SW1

    Bridge ID         priority   32769         mac add  000c.3045.4180

    interface          role   state   cost        prio.nbr   type

    Fa0/13            root   FWD     19         128.13    p2p

    Fa0/14            ALTN   BLK     19         128.14    p2p   

    Fa0/15            ALTN   BLK     19         128.15    p2p

    Fa0/19            Desg   FWD     19         128.19    p2p

    Fa0/20            Desg   FWD     19         128.20    p2p

    Fa0/21            Desg   FWD     19         128.21    p2p 

    on SW4#sh span vlan 1

    VLAN001      

    spanning tree enable protocol ieee

    Root bridge           SW1

    Bridge ID         priority   32769         mac add  000c.3045.d600

    interface          role   state   cost        prio.nbr   type

    Fa0/16            ALTN   BLK     19         128.16    p2p

    Fa0/17            ALTN   BLK     19         128.17    p2p   

    Fa0/18            ALTN   BLK     19         128.18    p2p

    Fa0/19            Desg   FWD     19         128.19    p2p

    Fa0/20            ALTN   BLK     19         128.20    p2p

    Fa0/21            ALTN   BLK     19         128.21    p2p   

     

     

    so why SW2,SW3 and SW4 is electing these ports in this given result?

    why prio.nbr shown differ from others on SW1 and SW2?

     

  • Everybody in this thread has answer your question in detailed way. if you still don't understand I would like to recommend you to go through the INE Switch Bootcamp by Brian Mcgahan, where he taught the Spanning Tree Protocol in a very fundmantal way. 

    Happy Studying

  • Friend, give some time urself on this post. Where you will learn about Spanning-tree, every thing is explained with good topology.

    http://ieoc.com/forums/t/16429.aspx
    http://ieoc.com/forums/t/16384.aspx

     

    [:D]

     

    in same scenario,

    SW3-fa0/13,14,15-------fa0/16,17,18-SW1-fa0/13,14,15----------fa0/13,14,15-SW2-fa0/19,20,21--------fa0/16,17,18-SW4-fa0/16,17,18-----fa0/16,17,18-SW3

     

    on SW1#sh span vlan 1

    VLAN001      

    spanning tree enable protocol ieee

    Root bridge           SW1

    Bridge ID         priority   32769         mac add  001b.d490.7c00

    interface          role   state   cost        prio.nbr   type

    Fa0/13            Desg   FWD     19         128.15    p2p

    Fa0/14            Desg   FWD     19         128.16    p2p   

    Fa0/15            Desg   FWD     19         128.17    p2p

    Fa0/16            Desg   FWD     19         128.18    p2p

    Fa0/17            Desg   FWD     19         128.19    p2p

    Fa0/18            Desg   FWD     19         128.20    p2p 

     

     

    on SW2#show spanning vlan 1

    VLAN001

    spanning tree enable protocol ieee

    root bridge          SW1

    bridge id        priority        32769   mac add  001b.d490.7c00

    interface          role   state   cost        prio.nbr   type

    Fa0/13            root   FWD     19         128.15    p2p

    Fa0/14            ALTN   BLK     19         128.16    p2p   

    Fa0/15            ALTN   BLK     19         128.17    p2p

    Fa0/19            Desg   FWD     19         128.21    p2p

    Fa0/20            Desg   FWD     19         128.22    p2p

    Fa0/21            Desg   FWD     19         128.23    p2p

     

    on SW3#sh span vlan 1

    VLAN001      

    spanning tree enable protocol ieee

    Root bridge           SW1

    Bridge ID         priority   32769         mac add  000c.3045.4180

    interface          role   state   cost        prio.nbr   type

    Fa0/13            root   FWD     19         128.13    p2p

    Fa0/14            ALTN   BLK     19         128.14    p2p   

    Fa0/15            ALTN   BLK     19         128.15    p2p

    Fa0/19            Desg   FWD     19         128.19    p2p

    Fa0/20            Desg   FWD     19         128.20    p2p

    Fa0/21            Desg   FWD     19         128.21    p2p 

    on SW4#sh span vlan 1

    VLAN001      

    spanning tree enable protocol ieee

    Root bridge           SW1

    Bridge ID         priority   32769         mac add  000c.3045.d600

    interface          role   state   cost        prio.nbr   type

    Fa0/16            ALTN   BLK     19         128.16    p2p

    Fa0/17            ALTN   BLK     19         128.17    p2p   

    Fa0/18            ALTN   BLK     19         128.18    p2p

    Fa0/19            Desg   FWD     19         128.19    p2p

    Fa0/20            ALTN   BLK     19         128.20    p2p

    Fa0/21            ALTN   BLK     19         128.21    p2p   

     

     

    so why SW2,SW3 and SW4 is electing these ports in this given result?

    why prio.nbr shown differ from others on SW1 and SW2?

     

     

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