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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter9 Creating and Maintai nin g VLA Ns Using the VLAN Trunking Protocol

VLAN Port Membership Modes

You configure a port to belong to a VLAN by assigning a membership mode that determines the kind of
traffic the port carries and the number of VLANs to which it can belong. Table 9- 1 lists the membership
modes and characteristics.
For more detailed definitions of the modes and their functions, see Table 9-6 on page 9-23.
When a port belongs to a VLAN, the switch learns and manages the addresses associated with the port
on a per-VLAN basis. For more information, see the “Managing the MAC Address Table” section on
page 6-51.
Using the VLAN Trunking Protocol
VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the
addition, deletion, and renaming of VLANs on a network-wide basis. VTP minimizes misconfi gurations
and configuration inconsistencies that can cause several problems, such as duplicate VLAN names,
incorrect VLAN-type specifications, and security violations.
Before you create VLANs, you must decide whether to use VT P in yo ur ne tw ork . Usi n g VT P, you can
make configuration changes centrally on one or more switches and have those changes automatically
communicated to all the other switches in the network. Without VTP, you cannot send information about
VLANs to other switches.
Table9-1 Port Membership Modes
Membership Mode VLAN Membership Characteristics
Static-access A static-access port can belong to one VLAN and is manuall y assigned by using the switchport mode
access interface configuration command.
For more information, see the “Assigning Static-Access Ports to a VLAN” section on page 9-19.
Trunk (ISL or
IEEE 802.1Q) A trunk is a member of all VLANs in the VLAN database by default, but membership can be lim ited by
configuring the allowed-VLAN list. You can also modify the pruning-eligible list to block flooded
traffic to VLANs on trunk ports that are included in the list.
VTP maintains VLAN configuration consistency by managing the addition, del etion , and re naming of
VLANs on a network-wide basis. VTP exchanges VLAN configuration message s wit h ot her swi tc hes
over trunk links.
Configure VLAN trunks using the switchport mode trunk interface configuration command. For mor e
information, see the “Configuring an Ethernet Interface as a Trunk Port” section on page 9-25.
Dynamic access A dynamic-access port can belong to one VLAN and is dynamically assigned by a V MPS. Th e V MPS
can be a Catalyst 5000 or Catalyst 6000 series switch, for example, but never a Catalyst 3550 switch.
You begin configuration by using the switchport mode access interface configuration command.
For more information, see the “Configuring an Interface as a Layer 2 Dynamic Access Port” sect ion on
page9-37.