11-08-2006 06:13 PM - edited 03-05-2019 12:42 PM
We have a 6500 and 4500, connected via a Dot11Q trunk. PVST is enabled on both ends. Here are the applicable config lines:
6500 (Sup720, 12.2(18)SXD7):
spanning-tree mode pvst
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
!
interface GigabitEthernet3/48
no ip address
switchport
switchport access vlan 2
switchport trunk native vlan 2
switchport mode trunk
switchport voice vlan 811
!
4500 (SupIV, 12.2(31)SG):
spanning-tree mode pvst
spanning-tree extend system-id
interface GigabitEthernet2/1
switchport access vlan 2
switchport trunk encapsulation dot1q
switchport trunk native vlan 2
!
It seems to be working, despite the 6500 being set as a trunk and 4500 being set as an access port. However when attached to the 6500 and running EtherReal, I see PVST+ packets being sent to the interface on my PC at a rate of about 10 every second. On the 4500, I see only the expected ARP broadcasts.
Is this type of traffic normal for PVST, or is this definitely a misconfiguration I should fix?
11-08-2006 09:32 PM
Hi,
Can you Please paste the output of " Show interface gig 3/48 switchport" and Show interface gig 2/1 switchport "
It is working because both the links have auto-negotiated the trunk. We will be able to clarify after looking at the outputs of the above commands requested.
HTH,
-amit singh
11-09-2006 09:29 AM
Sure, here is from the 6500:
Name: Gi3/48
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 2 (VLAN0002)
Trunking Native Mode VLAN: 2 (VLAN0002)
Voice VLAN: 811 (VLAN0811)
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Voice VLAN: 811 (VLAN0811)
Appliance trust: none
And from the 4500:
Name: Gi2/1
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 2 (VLAN0002)
Trunking Native Mode VLAN: 2 (VLAN0002)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk associations: none
Administrative private-vlan trunk mappings: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none
11-09-2006 09:37 AM
Hi,
As suggested in earlier post, It is working as both the interface has negotiated on the trunk mode using DTP (Dynamic trunking protocol) which is enabled by default on the switch interfaces. Check the " operational Mode:Trunk" and " negotiation of Trunking:ON" status.
Switch sends the STP Bpdu out all the switch interfaces.So when you are using sniffer on the port and looking up some of the STP traffic that is normal.
HTH, Please rate if it does.
-amit singh
11-09-2006 12:47 PM
Interesting. Would MIST or RSTP have the same behavior?
11-09-2006 04:11 PM
RSTP would don't know about mist . A few spanning tree packets on aport is not going to hurt anything performance wise on a 100 meg port . It will save your behind if someone miswires something .
11-10-2006 11:24 AM
I guess my question is why are the PVST+ packets being seen on the 6500 but not the 4500?
Another odd thing I noticed is the spanning tree root appears to be set to a Dell switch inside a blade server. Obviously, our spanning tree root should be the 6500 and I'm working on correcting that.
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