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All participating VLANs get removed from STP after deleting one port+vlan alone from STP domain.

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TitleAll participating VLANs get removed from STP after deleting one port+vlan alone from STP domain.
Symptoms
Please see the below configuration. Port 10 is tagged in two VLANs - 'v10' and 'v20'. 

* X460G2-24t-G4.2 # create vlan v10

* X460G2-24t-G4.3 # configure vlan v10 tag 12
* X460G2-24t-G4.4 # create vlan v20
* X460G2-24t-G4.6 # configure vlan v20 tag 13
* X460G2-24t-G4.7 # configure vlan v10 add ports 10 tagged
* X460G2-24t-G4.8 # configure vlan v20 add ports 10 tagged
* X460G2-24t-G4.9 #
* X460G2-24t-G4.9 #
* X460G2-24t-G4.9 # show vlan
Untagged ports auto-move: Inform
-----------------------------------------------------------------------------------------------
Name            VID  Protocol Addr       Flags                         Proto  Ports  Virtual
                                                                              Active router
                                                                              /Total
-----------------------------------------------------------------------------------------------
Default         1    10.10.10.100   /24  -f----------T---------------  ANY    1 /34  VR-Default
Mgmt            4095 10.127.20.80   /24  ----------------------------  ANY    1 /1   VR-Mgmt
nt_login        4094 ------------------------------------------------  ANY    0 /0   VR-Default
v10           12   ------------------------------------------------  ANY    1 /1   VR-Default
v20           13   ------------------------------------------------  ANY    1 /1   VR-Default
-----------------------------------------------------------------------------------------------
Flags : (B) BFD Enabled, (c) 802.1ad customer VLAN, (C) EAPS Control VLAN,
        (d) Dynamically created VLAN, (D) VLAN Admin Disabled,
        (e) CES Configured, (E) ESRP Enabled, (f) IP Forwarding Enabled,
        (F) Learning Disabled, (i) ISIS Enabled,
        (I) Inter-Switch Connection VLAN for MLAG, (k) PTP Configured,
        (l) MPLS Enabled, (L) Loopback Enabled, (m) IPmc Forwarding Enabled,
        (M) Translation Member VLAN or Subscriber VLAN, (n) IP Multinetting Enabled,
        (N) Network Login VLAN, (o) OSPF Enabled, (O) Virtual Network Overlay,
        (p) PIM Enabled, (P) EAPS protected VLAN, (r) RIP Enabled,
        (R) Sub-VLAN IP Range Configured, (s) Sub-VLAN, (S) Super-VLAN,
        (t) Translation VLAN or Network VLAN, (T) Member of STP Domain,
        (v) VRRP Enabled, (V) VPLS Enabled, (W) VPWS Enabled, (Z) OpenFlow Enabled
 
Total number of VLAN(s) : 5
* X460G2-24t-G4.10 #
* X460G2-24t-G4.10 #
* X460G2-24t-G4.10 # configure stpd s0 mode dot1w
* X460G2-24t-G4.11 # enable s0
* X460G2-24t-G4.12 # disable s0
* X460G2-24t-G4.13 # enable stpd s0 auto-bind vlan
  <vlan_name>     VLAN name
    "Default"  "Mgmt"  "nt_login"  "v10"  "v20"
  <vlan_list>     VLAN list (1-4094)
* X460G2-24t-G4.13 # enable stpd s0 auto-bind vlan 12
* X460G2-24t-G4.14 # enable stpd s0 auto-bind vlan 13
* X460G2-24t-G4.16 # configure stpd s0 add vlan 12 ports 10
* X460G2-24t-G4.17 # configure stpd s0 add vlan 13 ports 10
* X460G2-24t-G4.18 # enable s0
* X460G2-24t-G4.19 # show s0
Stpd: s0                Stp: ENABLED            Number of Ports: 34
Rapid Root Failover: Disabled
Operational Mode: 802.1W                        Default Binding Mode: 802.1D…………………………….> [As per the User Guide, dot1w mode and dot1d binding mode are compatible with each other.]
802.1Q Tag: (none)
Ports: 1,2,3,4,5,6,7,8,9,10,
       11,12,13,14,15,16,17,18,19,20,
       21,22,23,24,25,26,27,28,29,30,
       31,32,33,34
Participating Vlans: Default,v10,v20………………………[we have 3 participating VLANs prior to that port being deleted from the STP domain.]  
Auto-bind Vlans: Default,v10,v20
Bridge Priority            : 32768              Bridge Priority Mode: 802.1t
Operational Bridge Priority: 32768
BridgeID                   : 80:00:00:04:96:99:72:8a
Designated root            : 80:00:00:04:96:99:72:8a
RootPathCost: 0         Root Port     : ----
MaxAge      : 20s       HelloTime     : 2s      ForwardDelay     : 15s
CfgBrMaxAge : 20s       CfgBrHelloTime: 2s      CfgBrForwardDelay: 15s
Topology Change Time           : 35s            Hold time        : 1s
Topology Change Detected       : FALSE          Topology Change  : FALSE
Number of Topology Changes     : 0
Time Since Last Topology Change: 0s
Topology Change initiated locally on Port none
Topology Change last received on Port none from none
Backup Root               : Off         Backup Root Activated  : FALSE
Loop Protect Event Window : 180s        Loop Protect Threshold : 3
New Root Trap             : On          Topology Change Trap   : Off
Tx Hold Count             : 6
* X460G2-24t-G4.20 #
* X460G2-24t-G4.20 #
* X460G2-24t-G4.20 # configure s0 delete vlan 12 ports 10……………………………………….> [As you can see once I delete port 10 from VLAN 12, all participating VLANs, except VLAN default are removed.]
WARNING: Deleting carrier vlan v10, port 10 and all protected vlans on this port
* X460G2-24t-G4.21 #
* X460G2-24t-G4.21 # show s0
Stpd: s0                Stp: ENABLED            Number of Ports: 33
Rapid Root Failover: Disabled
Operational Mode: 802.1W                        Default Binding Mode: 802.1D
802.1Q Tag: (none)
Ports: 1,2,3,4,5,6,7,8,9,11,
       12,13,14,15,16,17,18,19,20,21,
       22,23,24,25,26,27,28,29,30,31,
       32,33,34
Participating Vlans: Default
Auto-bind Vlans: Default,v10,v20
Bridge Priority            : 32768              Bridge Priority Mode: 802.1t
Operational Bridge Priority: 32768
BridgeID                   : 80:00:00:04:96:99:72:8a
Designated root            : 80:00:00:04:96:99:72:8a
RootPathCost: 0         Root Port     : ----
MaxAge      : 20s       HelloTime     : 2s      ForwardDelay     : 15s
CfgBrMaxAge : 20s       CfgBrHelloTime: 2s      CfgBrForwardDelay: 15s
Topology Change Time           : 35s            Hold time        : 1s
Topology Change Detected       : FALSE          Topology Change  : FALSE
Number of Topology Changes     : 0
Time Since Last Topology Change: 0s
Topology Change initiated locally on Port none
Topology Change last received on Port none from none
Backup Root               : Off         Backup Root Activated  : FALSE
Loop Protect Event Window : 180s        Loop Protect Threshold : 3
New Root Trap             : On          Topology Change Trap   : Off
Tx Hold Count             : 6



 
Environment
  • EXOS 22.4
  • Summit
  • Blackdiamond
Cause
The code implementation is like, when the carrier vlan gets removed from the stpd domain, all other member/participating vlans should get removed from the stpd domain.

Prior to EXOS 22.2, for port encapsulation mode as "dot1d", at least one untagged vlan was required to be present in the stpd domain and that vlan was considered as the carrier vlan. So in this case, when this untagged carrier vlan gets removed from the stpd domain, all other participating vlans from the stpd domain will get removed as expected.

But from EXOS 22.2 onwards, for encapsulation mode as dot1d, there is no such restriction of having at least one vlan as untagged. It can support both(tagged/untagged) and there is no concept of control vlan. So that when any tagged vlan was getting removed from the stpd domain, it was considered as the control vlan and all other participating vlans were getting removed from the stpd domain.

- This is a bug and is documented in CR#xos0074481. 
Resolution
The fix is to upgrade to 22.7 and higher. 
Additional notes

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