Trunk Ports; Switch Virtual Interfaces - Cisco Catalyst 2975 Software Configuration Manual
Ios release 12.2(55)se
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Chapter 12
Configuring Interface Characteristics
Supported access ports:
•
•
You can also configure an access port with an attached Cisco IP Phone to use one VLAN for voice traffic
and another VLAN for data traffic from a device attached to the phone. For more information about
voice VLAN ports, see
Trunk Ports
A trunk port carries the traffic of multiple VLANs and by default is a member of all VLANs in the VLAN
database.
The switch supports only 802.1Q trunk ports. An 802.1Q trunk port supports simultaneous tagged and
untagged traffic. The trunk port is assigned a default port VLAN ID (PVID), and all untagged traffic
travels on the port default PVID. All untagged traffic and tagged traffic with a NULL VLAN ID belong
to the port default PVID. A packet with a VLAN ID equal to the outgoing port default PVID is sent
untagged. All other traffic is sent with a VLAN tag.
Although by default, a trunk port is a member of every VLAN known to the VTP, you can limit VLAN
membership by configuring an allowed list of VLANs for each trunk port. The list of allowed VLANs
affects only the associated trunk port. By default, all possible VLANs (VLAN ID 1 to 4094) are in the
allowed list. A trunk port can become a member of a VLAN only if VTP knows of the VLAN and if the
VLAN is enabled. If VTP learns of a new, enabled VLAN and the VLAN is in the allowed list, the trunk
port automatically becomes a member of that VLAN. Traffic is forwarded to and from the trunk port for
that VLAN. If VTP learns of an enabled VLAN that is not in the allowed list for a trunk port, the port
does not become a member of the VLAN, and traffic for the VLAN is not forwarded to or from the port.
For more information about trunk ports, see
Switch Virtual Interfaces
A switch virtual interface (SVI) represents a VLAN of switch ports as one interface to the routing or
bridging function in the system. You can associate only one SVI with a VLAN. You configure an SVI
for a VLAN only to route between VLANs or to provide IP host connectivity to the switch.
By default, an SVI is created for the default VLAN (VLAN 1) to permit remote switch administration.
Additional SVIs must be explicitly configured.
You cannot delete interface VLAN 1.
Note
SVIs provide IP host connectivity only to the system.Beginning with Cisco IOS Release 12.2(55)SE, you
can enable routing and configure static routes on SVIs.
OL-19720-02
Static access ports are manually assigned to a VLAN (or through a RADIUS server for use with
IEEE 802.1x). For more information, see the
section on page
10-17.
VLAN membership of dynamic access ports is learned through incoming packets. By default, a
dynamic access port is not a member of any VLAN. Traffic forwarding to and from the port is
enabled only when the port VLAN membership is discovered. Dynamic access ports on the switch
are assigned to a VLAN by a VLAN Membership Policy Server (VMPS). The VMPS can be a
Catalyst 6500 series switch. The Catalyst 2975 switch cannot be a VMPS server.
Chapter 14, "Configuring Voice VLAN."
"802.1x Authentication with VLAN Assignment"
Chapter 13, "Configuring VLANs."
Catalyst 2975 Switch Software Configuration Guide
Understanding Interface Types
12-3
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