Hi guys,
I have implemented a network which consists of a core switch and some access switches. All the access switches are connected to the core switch through two interfaces.
I have set the core switch as the root bridge with priority 0 for STP, and I can see STP is working fine and the core switch is the root. However, when I have added a new access switch and connected to the core switch, the new access switch has become the root. I don't know why since the priority of the core switch is 0 and the priority of the new access switch is the default (7). The configuration is very simple since I only have created the vlans and enable STP. What can be the reason of this?
Here you are some outputs from the core switch (CORE-Stack-3810M) and the new access switch (Piso5DC-2930F-24G-PoEP-4SFPP). I have attached these outputs and the switchs' configs.
Piso5DC-2930F-24G-PoEP-4SFPP# show spanning-tree
Spanning Tree Information
STP Enabled [No] : Yes
Mode : RPVST
Extended System ID : Enabled
Ignore PVID Inconsistency : Disabled
RPVST Enabled VLANs : 1,100
Switch MAC Address : 98f2b3-b7cae0
Root Guard Ports :
Loop Guard Ports :
TCN Guard Ports :
BPDU Protected Ports :
BPDU Filtered Ports :
Auto Edge Ports : 1-28
Admin Edge Ports :
VLAN Root Mac Root Root Root Hello
ID Address Priority Path-Cost Port Time(sec)
----- --------------- ---------- ---------- -------------------- ---------
1 98f2b3-b7cae0 32,768 0 This switch is root 2
100 98f2b3-b7cae0 32,768 0 This switch is root 2
Piso5DC-2930F-24G-PoEP-4SFPP#
CORE-Stack-3810M# show spanning-tree config
Spanning Tree Information
STP Enabled [No] : Yes
Mode : RPVST
Extended System ID : Enabled
Ignore PVID Inconsistency : Disabled
Default Path Cost [8021t] : 8021.t
RPVST Enabled VLANs : 1,100
Switch MAC Address : ecebb8-1f5865
Root Guard Ports :
Loop Guard Ports :
TCN Guard Ports :
BPDU Protected Ports :
BPDU Filtered Ports :
Auto Edge Ports : 1/1-1/16,2/1-2/16
Admin Edge Ports :
Max Age Forward Hello Admin Root
VLAN Priority (sec) Delay(sec) Time(sec) Bridge
---- -------- ------- ---------- --------- ----------------
1 32768 20 15 2 Not Configured <<<<< shouldn't be 4096 for the root?
100 32768 20 15 2 Not Configured <<<<< shouldn't be 4096 for the root?
Regards,
Julián