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VDX6740 logical chassis spanning-tree and port-channel strange behaviour

  • 9 November 2020
  • 1 reply
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Hi all,

we have n.4 VDX6740 in logical chassis mode with two of them R41-1 and R41-2 connect to Cisco switches in Upstream using Port-Channel the other two, R42-1-and R42-2 are connect only to storage server and not connect to any other external switch. At the moment we have only one Port-Channel connect to Cisco because when we connect the other Port-Channel a loop happen and network freezed. Doing some throubleshooting we have seen that one switch, R42-2, see itself as spanning-tree root brdge while the other one sees Cisco switch as root bridge correctly. Also doing show  interface port-channel on R41-1 and R41-2 we see the output but doing the same command on R42-1 and R42-2 we didn’t see any output as reported below

R41-1# show interface port-channel 3
Port-channel 3 is up, line protocol is up
Hardware is AGGREGATE, address is c4f5.7c0f.9a72
    Current address is c4f5.7c0f.9a72
Description: aci-r31-2 Te13/3-Te13/2
Interface index (ifindex) is 671088643

R41-2# show interface port-channel 3
Port-channel 3 is up, line protocol is up
Hardware is AGGREGATE, address is c4f5.7c0f.9a72
    Current address is c4f5.7c0f.9a72
Description: aci-r31-2 Te13/3-Te13/2
Interface index (ifindex) is 671088643

R42-1# show interface port-channel 3
R42-1# 

R42-2# show interface port-channel 3
R42-2# 

R42-2# show spanning-tree  
VLAN 1

 Spanning-tree Mode: PVST Protocol

 Root Id: f001.01e0.5200.01ae (self)
 Bridge Id: f001.01e0.5200.01ae

The fabric is correctly formed we don’t understand which can be the problem..what can we do? Thanks Riccardo

R41-1# show vcs 
Config Mode    : Distributed
VCS Mode       : Logical Chassis
VCS ID         : 1
VCS GUID       : 425179a2-b284-4783-be98-7eaa20073208
Total Number of Nodes           : 4
Rbridge-Id       WWN                            Management IP   VCS Status       Fabric Status        HostName
--------------------------------------------------------------------------------------------------------------
1               >10:00:B4:2D:56:0B:BD:0C*       172.16.132.25   Online           Online               R41-1
2                10:00:C4:F5:7C:0F:9A:28        172.16.132.26   Online           Online               R41-2
3                10:00:50:EB:1A:F8:B5:30        172.16.132.27   Online           Online               R42-1
4                10:00:50:EB:1A:DC:FD:F0        172.16.132.28   Online           Online               R42-2
R41-1# 

 

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Best answer by Sam Pirok 16 December 2020, 16:48

Hello, my apologies for the long wait here.  STP configuration is usually simple, it just get enabled on port or not.  Normally, we recommend not enabling STP for the VCS fabric. If it is enabled, we recommend that you do it on the access switches.  A more complicate issue with enabling STP on the VDX is the interop with Cisco PVST with their proprietary mac in the BPDU.  I’d recommend opening a case for this so our engineers can go through the data to see what the problem can be as R41-1 and R41-2 are seeing the Cisco as the root bridge, while R42-2 is isolated and report as the root bridge.

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Hello, my apologies for the long wait here.  STP configuration is usually simple, it just get enabled on port or not.  Normally, we recommend not enabling STP for the VCS fabric. If it is enabled, we recommend that you do it on the access switches.  A more complicate issue with enabling STP on the VDX is the interop with Cisco PVST with their proprietary mac in the BPDU.  I’d recommend opening a case for this so our engineers can go through the data to see what the problem can be as R41-1 and R41-2 are seeing the Cisco as the root bridge, while R42-2 is isolated and report as the root bridge.