VLAN pruned and then not pruned on SW4, vtp transparent mode

Hi folks,

I'm trying to figure out what I just encountered.  I'm running through WB1 MPLS, and at the very first task I hit a snag - for some reason I can't ping across vrf VPN_B.  I spent quite a while TSing my configs and vrf since I assumed I had done something stupid there.

After quadruple checking everything, I started looking elsewhere.  Looking on switches 1 - 4, I looked at the vlans to make sure I had added VLAN 76 (required for the vrf) and sure enough I had.  I then looked at interface trunk, and sure enough, there on sw4 in the "forwarding state and not pruned" list, 76 is missing.

I do a show run to make sure there's nothing sneaky on the interfaces, and there's not - just totally standard config.  I then do a show vtp status to verify that info - it's running vtp v1 in transparent state.  I then run show int trunk again, just to make sure I wasn't seeing things, and all of a sudden, vlan 76 is there and I can ping across my vrf.

Now, clearly, I should have looked at vlans a lot earlier than I did, but I'm trying to figure out what would have caused pruning on a transparent switch to begin with, and more to the point, what would have caused it to suddenly include the vlan.  I'm used to occasionally having to clear stuck routes by clearing them - is there a similar command to "clear ip route *" for vlans that I don't know about?



  • I have not had similar experience with this, but I do not believe there is a command to similar to clear ip route * for vlan's, as all the vlan's reside in a vlan.dat file. If you cleared that file, you would have to re-create all the vlan information manually as it is not dynamic in transparent state.

    One question I have is, when did you put the switch in the Transparent state? If the switch was a client prior to that in a VTP domain and used all settings from a server, it may not have taken the change, or they may have been a dropped VTP packet that contained the pruning information. I would also have been curious to see the revision number of the vtp database.

  • For the MPLS labs in workbook 1 the switches start in transparent state.

    I'm just going to assume I did something stupid (like fail to exit out of vlan mode after creating the vlan) since I'm running on fumes and full of allergy meds.  The alternative would be that somehow doing a show run or show vtp status caused magic to happen, and that seems sort of unlikely.

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