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Author Topic: Cisco 3550 vs. D-Link DGS-3612G: problems with RSTP - incorrect root chosen  (Read 14276 times)

nexus-it

  • Level 1 Member
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  • Posts: 1

Hi everybody,

I have configured a D-Link mesh topology, based on 2 L3 switches (DGS-3612G) running VRRP and RSTP.
We have ~10 D-Link DES3200-10 switches connected to this mesh (1 GB to each core switch), as well as 2 Cisco switches, which are connected each one only to one of the DGS switches.

All the inter-switch traffic is tagged (including VLAN1)

Example configuration of Cisco port (towards the D-link)
interface GigabitEthernet0/1
 switchport encapsulation dot1q
 switchport mode trunk
 no spanning-tree portfast

Example configuration of D-Link

config vlan default delete 1-12
create vlan default tag 1
create vlan vlan2 tag 2
create vlan vlan3 tag 3
config vlan default add tagged 1-12
config vlan vlan2 add tagged 1-12
config vlan vlan3 add tagged 1-12

The D-Link switch #1 was configured both as VRRP master and STP root
by changing the priority of instance 0 to 4096 instead of 32768 (and priority 8192 on #2)

core1:5#show stp instance   
Command: show stp instance

 STP Instance Settings
 ---------------------------
 Instance Type          : CIST   
 Instance Status        : Enabled
 Instance Priority      : 0    (Bridge Priority : 0    , SYS ID Ext : 0 )

 STP Instance Operational Status
 --------------------------------
 Designated Root Bridge : 0    /00-1E-58-DC-20-00
 External Root Cost     : 0                     
 Regional Root Bridge   : 0    /00-1E-58-DC-20-00
 Internal Root Cost     : 0                     
 Designated Bridge      : 0    /00-1E-58-DC-20-00
 Root Port              : None 
 Max Age                : 20                     
 Forward Delay          : 15                     
 Last Topology Change   : 3108                   
 Topology Changes Count : 65             



All the D-Link 3200s successfully interchange traffic between all VLANs
However, the Cisco switches behave very strange:
For VLAN1, indeed, the Core#1 switch is chosen as root
However, for the rest of VLANs, the Cisco switch of the highest model becomes root:

---------------- -------------------- ------ ----- --- ---  ----------------
VLAN0001             0 001e.58dc.2000  20019    2   20  15  Fa0/16               
VLAN0002         32770 000e.3889.ae80      0    2   20  15
VLAN0003         32771 000e.3889.ae80      0    2   20  15                       

STP mode on all switches is configured as RSTP
Extend SystemID is enabled and cannot be disabled on the Cisco switches.

How can I cause the D-Link core switches to become STP root for all VLANs?

Thanks for reading till the end?
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Fatman

  • Poweruser
  • Level 9 Member
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  • Posts: 1675

If you have spanning trees per VLAN you are using MSTP not RSTP.  In mixed environment the default instance of MSTP is compatible with RSTP devices.  I would say that is what is happening.

P.S. The highest model number shouldn't be the deciding factor it should be the highest MAC.
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non progredi est regredi

Adams

  • Level 1 Member
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  • Posts: 5

Hi
Could you please tell how you did the inter-vlan routing in the Layer 3 Dlink Switch
Thanks in advance
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