Chapter 13 Configuring VLANs

Understanding VLANs

Supported VLANs

The switch supports VLANs in VTP client, server, and transparent modes. VLANs are identified by a number from 1 to 4094. VLAN IDs 1002 through 1005 are reserved for Token Ring and FDDI VLANs. VTP only learns normal-range VLANs, with VLAN IDs 1 to 1005; VLAN IDs greater than 1005 are extended-range VLANs and are not stored in the VLAN database. The switch must be in VTP transparent mode when you create VLAN IDs from 1006 to 4094.

Although the switch or switch stack supports a total of 1005 (normal range and extended range) VLANs, the number of routed ports, SVIs, and other configured features affects the use of the switch hardware.

The switch supports per-VLAN spanning-tree plus (PVST+) or rapid PVST+ with a maximum of 128 spanning-tree instances. One spanning-tree instance is allowed per VLAN. See the “Normal-Range VLAN Configuration Guidelines” section on page 13-6for more information about the number of spanning-tree instances and the number of VLANs. The switch supports both Inter-Switch Link (ISL) and IEEE 802.1Q trunking methods for sending VLAN traffic over Ethernet ports.

VLAN Port Membership Modes

You configure a port to belong to a VLAN by assigning a membership mode that specifies the kind of traffic the port carries and the number of VLANs to which it can belong. Table 13-1lists the membership modes and membership and VTP characteristics.

Table 13-1

Port Membership Modes and Characteristics

 

 

 

 

Membership Mode

VLAN Membership Characteristics

VTP Characteristics

 

 

 

 

Static-access

 

A static-access port can belong to one VLAN and is

VTP is not required. If you do not want VTP

 

 

manually assigned to that VLAN.

to globally propagate information, set the

 

 

For more information, see the “Assigning Static-Access

VTP mode to transparent. To participate in

 

 

Ports to a VLAN” section on page 13-11.

VTP, there must be at least one trunk port on

 

 

the switch or the switch stack connected to

 

 

 

 

 

 

a trunk port of a second switch or switch

 

 

 

stack.

 

 

 

 

Trunk (ISL or

 

A trunk port is a member of all VLANs by default,

VTP is recommended but not required. VTP

IEEE 802.1Q)

 

including extended-range VLANs, but membership can

maintains VLAN configuration consistency

 

 

be limited by configuring the allowed-VLAN list. You

by managing the addition, deletion, and

 

 

can also modify the pruning-eligible list to block flooded

renaming of VLANs on a network-wide

 

 

traffic to VLANs on trunk ports that are included in the

basis. VTP exchanges VLAN configuration

 

 

list.

messages with other switches over trunk

 

 

For information about configuring trunk ports, see the

links.

 

 

 

 

 

“Configuring an Ethernet Interface as a Trunk Port”

 

 

 

section on page 13-19.

 

 

 

 

 

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

 

OL-9775-02

13-3

 

 

 

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Cisco Systems 3750E manual Supported VLANs, Vlan Port Membership Modes, 13-3