Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Spanning-tree Uplinkfast question

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.

1 REPLY
New Member

Spanning-tree Uplinkfast question

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

204
Views
0
Helpful
1
Replies
CreatePlease login to create content