Displaying RPVST+ VLAN and vPort system limits

Each switch model supports a maximum number of active virtual ports (vPorts). New port VLAN memberships cannot be created once the vPort limit has been reached. Also, there is a maximum recommended number of active vPorts for each fixed-port switch or each module in a chassis switch. Exceeding the maximum recommended number of vPorts can result in dropped BPDUs and potential network loops. This command displays the current vPort status and maximum recommended vPort total per-switch or, for modular switches, per-module.

Syntax: 

show spanning-tree system-limits rapid-pvst

Displays the RPVST+ VLAN and virtual port (vPort) status on the switch.

Virtual Port Data Fields

vPort data field

Description

Count of Total Virtual Ports

The count of active vPorts (ports per VLAN) plus the count of non-active vPorts (all ports that belong to trunks).

Maximum Allowed Virtual Ports

The total of the system-created vPort instances plus the maximum user-assignable vPort instances. Each port on the switch belongs to at least one VLAN (VLAN-1 by default), which is a system-created vPort instance. The user-assigned VPORT instances are in addition to the system-assigned vPort instances. The show spanning-tree system-limits rapid-pvst command combines the system-created vPort instances and the user-assigned maximum vPort instances when calculating the maximum allowed virtual ports.

Each user-configured trunk on the switch increments this value by 1.

Current Virtual Ports

The number of ports that are members of each VLAN on a per-module basis (or a per-group of ports basis).

Operational Virtual Ports

The number of ports belonging to each PVST-enabled VLAN on a per-module basis (or a per-group of ports basis). This value should not exceed the recommended maximum vPort limit.

Recommended Maximum Virtual Ports

The maximum recommended number of vPort instances that should be allowed on the switch. Exceeding this limit can potentially result in received BPDUs being dropped.

Configuring vPorts

Virtual ports on a switch are calculated as ports per-VLAN. Also, a trunk membership on one or more VLANs counts as one vPort per-VLAN, regardless of how many physical ports belong to the trunk. For example, the following configuration on a modular chassis results in 26 vPorts. 

trunk 1,2 trk1
vlan 1
   name "DEFAULT_VLAN"
   untagged 3-24
   no untagged trk1
   exit
vlan 20
   ip address 10.243.230.75 255.255.255.248
   name "VLAN20"
   tagged trk1
   exit
vlan 30
   ip address 10.243.230.83 255.255.255.248
   name "VLAN30"
   tagged 13,14,trk1
   exit
  Module “A” Module “B” Module “C” Total vPorts on the Switch
VLAN 1 22 (A3 - A24) 23 (B2 - B24) 24 (C1 - C24)  
VLAN 20 1 (trk1: A1 - A2) 1 (trk1: B1)11 0  
VLAN 30 2 (A13 - A14) 1 (trk1: A1 - A2)11 2 (B13 - B14) 1 (trk1: B1)11 0  
vPorts per-module 26 27 24 77
1

A trunk in a given VLAN counts as one vPort for each module on which it occurs.

Exceeding a vPort recommended maximum

In a modular switch, if the vPort count for a given module exceeds the recommended limit for that module, a warning message is displayed in the CLI and an Event Log message is generated. Also, the total vPort count on a switch cannot exceed the maximum vPort count for the switch.

NOTE:

The output of show spanning-tree system-limits rapid-pvst shows a Maximum Allowed Virtual Ports value as a larger number than the values quoted in this table. This is because each port on the switch belongs to at least one VLAN (VLAN-1 by default) and this is a system created vPort instance.

Calculating non-active vPorts

Every port that is part of a manually configured trunk is counted as a non-active (reserved) vPort. For example, the ports in the following configuration are all non-active vPorts: 

trunk 1,2 trk1
trunk 3-5 trk2 lacp