05-31-2013 01:35 PM - edited 03-07-2019 01:40 PM
I've run into an odd problem - I have connected two 2960s together with copper on FastEthernet interfaces, and STP on the new switch immediately puts that port into blocking mode. I don't understand why this would be, since there is only one connection between the two, in fact, there is only one connection at all on the switch that is blocking. Does anyone have an explenation for this? I didn't think STP would block unless there is a loop, and there can't be a loop when there's only one link between the devices.
05-31-2013 02:30 PM
If you have 2 switches and that is the only cable attached to either switch then no it should not be blocking . Are there any other cables attched to either switch ?
05-31-2013 03:26 PM
Here's what I've got: "Switch A" is the existing device that is in operation. "Switch B" is the one hanging off Switch A.
Switch B has only one cable connected on Fa0/1, all others are empty and down. Switch B Fa0/1 is connected to Fa0/10 on Switch A. Switch B immediately puts that port into blocking mode.
Switch B "show span"
Switch#sh span
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 32778
Address 0019.2f94.d300
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0019.2f94.d300
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg BKN*19 128.1 P2p Edge *TYPE_Inc
Switch B Fa0/1 running config:
Switch#sh run int fa0/1
Building configuration...
Current configuration : 84 bytes
!
interface FastEthernet0/1
switchport access vlan 10
spanning-tree portfast
end
Switch A is in forwarding mode. Switch A "show span":
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address 0015.c626.af00
Cost 4
Port 25 (GigabitEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0027.0ca3.3e00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/3 Desg FWD 19 128.3 P2p Edge
Fa0/10 Desg FWD 19 128.10 P2p Edge
Fa0/12 Desg FWD 19 128.12 P2p Edge
Gi0/1 Root FWD 4 128.25 P2p
Gi0/2 Desg FWD 4 128.26 P2p Edge
Switch A Show run int fa0/10:
USRDNZ07#sh run int fa0/10
Building configuration...
Current configuration : 237 bytes
!
interface FastEthernet0/10
switchport access vlan 10
switchport mode access
switchport voice vlan 100
srr-queue bandwidth share 10 10 60 20
priority-queue out
mls qos trust cos
auto qos voip trust
spanning-tree portfast
end
Any ideas?
05-31-2013 02:48 PM
What do you see when you run the command show interest status? Also as the previous poster said, if you only have one cable between two switches, one switch will be elected the root switch, and will have nothing but designated ports. The port on the other end, should be A root port. Can you post A show run of each interface and a show span?
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05-31-2013 03:47 PM
I've figured it out. I noticed that console output from Switch B was citing port-type inconsistency for reason for the block.
02:37:44: %SPANTREE-7-RECV_1Q_NON_TRUNK: Received 802.1Q BPDU on non trunk FastEthernet0/1 VLAN10.
02:37:44: %SPANTREE-7-BLOCK_PORT_TYPE: Blocking FastEthernet0/1 on VLAN0010. Inconsistent port type.
Switch#sh spanning-tree inconsistentports
Name Interface Inconsistency
-------------------- ------------------------ ------------------
VLAN0010 FastEthernet0/1 Port Type Inconsistent
Number of inconsistent ports (segments) in the system : 1
I think since I had a voice vlan configured on the Switch A port, Switch B interpereted it as a trunk port, even thought it was configured as access.
I removed the "sw voice vlan" statement from thh Switch A port, and after a shut/no shut on the interface, it came up without a problem.
Switch#show span
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address 0015.c626.af00
Cost 23
Port 1 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0019.2f94.d300
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1 Root FWD 19 128.1 P2p
Lesson learned.
05-31-2013 03:51 PM
For starters links connecting switches, which are considered by story to be point to point links should not be configured for port fast.
Second SWB has been elected the root switch, And on SWA, the best path cost to reach the root is from Gi0/1.
Take out the portfast command on the two Fa ports connecting the two switches and let us know what happens.
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05-31-2013 03:53 PM
Depending on the DTP modes, it was probably trying to form a trunk
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