Task 1.3 Pruning in SW2 not SW1 & SW3

The answer for is task seems to be incorrect for me because VLAN 8 is at SW2 switch so traffic from VLAN8 will come into SW2 and go to SW1 & SW3. By default, SW2 will prune its trunk links so traffic will not go to SW1 & SW3.

If we want traffic to go to SW1 & SW3, We need to remove VLAN8 from prune-eligible list in SW2, NOT in SW1 & SW3 as in the WB answer.

In fact, I think the answer must be:
SW2(config)# int range fa0/13 ,fa fa0/16
# switchport trunk pruning vlan remove 8

Any Idea?

Comments

  • This is the starting point - pruning is enabled and the pruning eligibility list is unchanged - we can see that vlan 8 is being prunned on SW2.

    Rack2SW1#show int f0/13 pruning

    Port Vlans pruned for lack of request by neighbor
    Fa0/13 7,77

    Port Vlan traffic requested of neighbor
    Fa0/13 1,7,12,45,77


    Rack2SW2#s int f0/13 pruning

    Port Vlans pruned for lack of request by neighbor
    Fa0/13 6,8,36,43,88,255,258

    Port Vlan traffic requested of neighbor
    Fa0/13 1,6,8,12,36,43,45,88,255,258

    If we remove vlan 8 from the pruning-list on SW1 we see that SW1 now requests vlan 8 of SW2 and SW2 removes vlan 8 from those that it prunes.


    Rack2SW1(config)#int range f0/13
    Rack2SW1(config-if-range)# sw trunk pruning vlan remove 8
    Rack2SW1(config-if-range)#end

    Rack2SW1#show int f0/13 prun

    Port Vlans pruned for lack of request by neighbor
    Fa0/13 7,77

    Port Vlan traffic requested of neighbor
    Fa0/13 1,7-8,12,45,77

    Rack2SW2#s int f0/13 pruning

    Port Vlans pruned for lack of request by neighbor
    Fa0/13 6,36,43,88,255,258 <-- VLAN 8 no longer pruned<br />
    Port Vlan traffic requested of neighbor
    Fa0/13 1,6,8,12,36,43,45,88,255,258


    If we remove the pruning configuration on SW1 and apply it to SW2. We see that SW1 no longer makes the request for vlan 8 and that SW2 simply removes vlan 8 from those prunned.

    Rack2SW2(config)#int range f0/13
    Rack2SW2(config-if-range)# sw trunk pruning vlan remove 8
    Rack2SW2(config-if-range)# end

    Rack2SW1#show int f0/13 prun

    Port Vlans pruned for lack of request by neighbor
    Fa0/13 7,77

    Port Vlan traffic requested of neighbor
    Fa0/13 1,7,12,45,77 <-- unchanged<br />

    Rack2SW2#s int f0/13 pruning

    Port Vlans pruned for lack of request by neighbor
    Fa0/13 6,36,43,88,255,258 <--- VLAN 8 not pruned<br />
    Port Vlan traffic requested of neighbor
    Fa0/13 1,6,8,12,36,43,45,88,255,258

    As far as I can see it - if you remove the vlan from the pruning-list on the switch that doesn't have the VLAN, SW1 in this case, then it requests the vlan. If you remove the vlan from the pruning-list on the switch that has the VLAN, SW2 in this case, then it floods VLAN traffic regardless.

    Removing vlan 8 from the puning eligible list on SW1 or SW2 has the same affect on what SW2 prunes. I would have thought either solutions were acceptable.

    rich
  • Thank Riche,
    Your Post is very clear and It helps me to understand more about VLAN Pruning.

    But, AS far as I know, VLan pruning will depend on spanning tree. If, for example, The root bridge for VLAN 8 is at SW4 and port 13 to 15 in SW2 are blocks. You can see that Vlan 8 traffic will not be sent directly to SW1, and the Pruning list will be NONE

    So to be correct for this Task in all circumstances, it is better to but SW2 as the root bridge for VLAN 8, and then we use the commands as in the WB.
  • nice explanation, thanks Rich!

    for those like me, when you see
     Quote:

    Rack1SW1(config-if)#switchport tr pruning vlan except 8
    Command rejected: Bad VLAN pruning list.


    you should refer to univercd and read that you must firstly create pruning list.
Sign In or Register to comment.