STP forwarding and pruning problem

[pokwan]

Hi,

Vlan 23 and 28 are trunked between Cisco 4500 and Cat 3750. On the Cisco 4500, these 2 vlans are available on the "Vlans in spanning tree forwarding state and not pruned" on sh int trunk. However, on the Cat 3750 these vlans does not appear on "Vlans in spanning tree forwarding state and not pruned" on sh int trunk (see below).

A sh vtp status shows that the vtp pruning mode is enabled. A device on vlan 28 are connected on the Cat 3750 but is not accessable. There are a few devides on vlan 23 on the Cat3730 which are accessable eventhough it wasn't in "Vlans in spanning tree forwarding state and not pruned".

Even with pruning mode enabled, with vlan 23 and 28 defined, these 2 vlans should be in "Vlans in spanning tree forwarding state and not pruned" .

Can someone explain why this is hapenning? Any help is much appreciated.

TIA.

PF

CISCO 4500#sh vlan

VLAN Name Status Ports

---- -------------------------------- --------- -------------------------------

1 default active Gi2/2

23 vlan_webserver active Gi4/3

25 vlan_server_client active Gi1/1

28 vlan_mgmt active Gi4/18

CISCO 4500#sh int trunk

Port Mode Encapsulation Status Native vlan

Gi2/1 desirable n-isl trunking 1

Port Vlans allowed on trunk

Gi2/1 1,23,25-28

Port Vlans allowed and active in management domain

Gi2/1 1,23,25-26,28

Port Vlans in spanning tree forwarding state and not pruned

Gi2/1 1,23,25-26,28

Catalyst 3750#sh vlan

VLAN Name Status Ports

---- -------------------------------- --------- -------------------------------

23 vlan_webserver active Fa2/0/17, Fa2/0/18, Fa2/0/19, Fa2/0/21

25 vlan_server_client active Fa1/0/1

26 vlan_server active

28 vlan_mgmt active Fa1/0/28

Catalyst 3750#sh int trunk

Port Mode Encapsulation Status Native vlan

Gi1/0/1 desirable n-isl trunking 1

Port Vlans allowed on trunk

Gi1/0/1 1,23,25-26,28

Port Vlans allowed and active in management domain

Gi1/0/1 1,23,25-26,28

Port Vlans in spanning tree forwarding state and not pruned

Gi1/0/1 1,25

[Kevin Dorrell]

Is it all working now? I notice from one of your postings that the 3750 is no longer pruning VLAN 28 from the trunk.

In you original posting, you said that if you connect a device to VLAN 28 on the 3750, then it is not accessible. When you did this show spanning-tree, there were no devices connected to the 3750 on VLAN 28. The only port in the Spanning-Tree on that VLAN was G1/0/1, which I guess is your uplink to the 4500.

What is the current status of this problem?

Kevin Dorrell

Luxembourg

[pokwan]

Kevin,

Sorry for not mentioning that it is working now. Now both the switches are in transparent mode as desired. I was able to made it work by disabling pruning on the 3750 but I do not quite understand then. Hence the posting on the website. Edison helped me understand what my problem was.

However, I still am confused as to why devices on vlan 23 works on the 3750 eventhough it did not appear on "Vlans in spanning tree forwarding state and not pruned" in sh trunk. Like Vlan 28, vlan 23 should not have worked either but it did.

There was a device on port fa2/0/28 connected to 3750 on vlan 28 (Wasn't copied properly).

Thanks.

PF