Viewing 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.

Viewing RPVST+ VLAN and vPort system limits

switch(config)# show spanning-tree system-limits rapid-pvst

 Spanning Tree Information


  STP Enabled              : Yes
  Mode                     : RPVST
  RPVST Enabled VLANs      : 20


  Switch MAC Address                   : 002347-c651c0
  Count of RPVST Enabled VLANs         : 1
  Maximum Allowed RPVST Enabled VLANs  : 400
  Count Of Total Virtual Ports         : 24
  Maximum Allowed Virtual Ports        : 424

                       Current         Operational     Recommended Maximum
  Ports                Virtual Ports   Virtual Ports   Virtual Ports
  -------------------- --------------- --------------- --------------------
  Ports 1-24           24              2               200

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 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. NOTE: 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)¹	0
VLAN 30	2 (A13 - A14) 1 (trk1: A1 - A2)¹	2 (B13 - B14) 1 (trk1: B1)¹	0
vPorts per-module	26	27	24	77

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

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
trunk 17-20 trk3 dt-lacp

Calculating per-module vPorts on chassis switches

The switch-wide active vPort count, there is a vPort count per port module determined by the number of ports per line card that are members of each VLAN. Also, on modular switches, if a VLAN includes a trunk configured with ports on more than one module, then one vPort is counted for each module on which the trunk exists (regardless of how many ports are included in the trunk.) For example, in the following configuration, VLANs 1, 20, and 30 have a total of 74 vPorts.

trunk A1,A2,B1 trk1
vlan 1
    name “DEFAULT_VLAN”
    untagged A3-A24, B2-B24
    no untagged trk1
    exit
vlan 20
    ip address 10.243.230.75 255.255.255.248
    name “VLAN20”
    tagged A3-A12, B2-B12, trk1
    exit
vlan 30
    ip address 10.243.230.83 255.255/255/248
    name “VLAN30”
    tagged A13, A14, B13, B14, trk1
    exit

	Module “A”	Module “B”	All Modules
VLAN 1	22	23	4
VLAN 20	10 + 1	11 + 1	23
VLAN 30	2 + 1	2 + 1	6
Total vPorts	36	38	74