07-25-2012 11:08 AM - edited 03-07-2019 07:58 AM
Hello Community,
I have Cisco Catalyst Swicth 2950T-24 and the following scenario:
Port fa 0/1 : Trunk VLANs 10,20,30 (Providing trunk access to another remote switch in the network in order to re-distribute to customer)
Port fa 0/2: Access VLAN 10 (Customer)
Port fa 0/3: Access VLAN 20 (Customer)
Port 0/4: Access VLAN 30 (Customer)
Port 0/23 : Trunk 10,20,30 (Upstream Primary)
Port 0/24: Trunk 10,20,30 (Upstream Secondary)
Below is the configuration sample:
spanning-tree mode pvst
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
spanning-tree uplinkfast
interface FastEthernet0/1
description To_Another_Swicth
switchport trunk allowed vlan 10,20,30
switchport mode trunk
!
interface FastEthernet0/2
description Customer_A
switchport access vlan 10
switchport mode access
!
interface FastEthernet0/3
description Customer_B
switchport access vlan 20
switchport mode access
!
interface FastEthernet0/3
description Customer_C
switchport access vlan 30
switchport mode access
!
interface FastEthernet0/23
description Link_to_Upstream_Swicth_Primary
switchport trunk allowed vlan 10,20,30
switchport mode trunk
!
interface FastEthernet0/24
description Link_to_Upstream_Swicth_Secondary
switchport trunk allowed vlan 10,20,30
switchport mode trunk
spanning-tree cost 20
!
Problem:
Whenever I enable the fa 0/24, link to another switch connected from fa 0/1 becomes unstable. Please help me to accomplish to set fa 0/23 as Primary Upstream port and fa 0/24 as secondary for backup.
Any help will be highly appreciated. Thanks in advance.
07-25-2012 06:43 PM
It sounds to me that fa0/1 is the current root port and that enabling fa0/24 provides a better path to the root bridge, thus blocking fa0/1.
Even if you set fa0/23 as the root port, the switch may still block fa0/1 and fa0/24.
I'd set the cost of fa0/1 and fa0/24 to be very high so that the bridge would prefer fa0/23. But like I said, fa0/24 and fa0/1 may still get blocked if they are alternate root ports.
-vg
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