What Are vPorts? How Are They Derived?

MVP Expert
MVP Expert
Q:

What are vPorts? How are they derived?



A:

Each switch model supports a maximum number of active virtual ports (vPorts).  Virtual ports on a switch are determined as per the VLAN port membership. 

A TRK port or a trunk port associated one or more VLANs counts as one vPort per-VLAN, regardless of how many physical interfaces are part of the trunk.

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.

 

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.

 

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

 

From the above Fixed-Port Switch example, the total number of vports are 26.  The same calculation applies for Chassis/Modular based Switches.

 

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.

 

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.

For example, on a 2930F 24G PoE+ 1sot Switch in the factory default configuration, the switch is already configured with 24 vPorts because all 24 ports are members of VLAN-1. The user assigned vPort instances are these system assigned vPort instances, meaning that 400 vPort instances can be created over and above the system-created vPort instances.

The show spanning-tree system-limits rapid-pvst command includes the system-created vPort instances and the user-assignable vPort instances when calculating the maximum vPorts on the switch. In the 2930F case, the maximum vPorts would be displayed as 424 (24 system + 400 user-assignable).

 

Exceeding a vPort recommended maximum

From the information we have 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.

 

Maximum VLANs and vPorts per-switch or per-module

Platform Maximum PVST-Enabled VLANs Maximum vPorts per device (User-Assignable) Maximum vPorts per Chassis Module or Fixed-Port Switch
       
2930F/2930M - 24, 48 128 400 2000+x (x being the number of logical ports in a vlan)
3810M - 24, 48 400 400 2000+x
5400R 400 400 2000+x
   

Virtual ports (vPorts) on a switch are determined by the number of physical ports on the switch, plus other factors. Exceeding the recommended number of vPorts can result in dropped BPDUs.

 

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Last update:
‎06-10-2019 07:39 AM
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