Tunnel Ports - Cisco Catalyst 3550 series Software Configuration Manual

Understanding Interface Types

Tunnel Ports

Tunnel ports are used in 802.1Q tunneling to segregate the traffic of customers in a service provider
network from other customers who appear to be on the same VLAN. You configure an asymmetric link
from a tunnel port on a service provider edge switch to an 802.1Q trunk port on the customer switch.
Packets entering the tunnel port on the edge switch, already 802.1Q-tagged with the customer VLANs,
are encapsulated with another layer of 802.1Q tag (called the metro tag) containing a VLAN ID unique
in the service provider network, for each customer. The double-tagged packets go through the
service-provider network keeping the original customer VLANs separate from those of other customers.
At the outbound interface, also a tunnel port, the metro tag is removed, and the original VLAN numbers
from the customer network are retrieved.
Tunnel ports cannot be trunk ports or access ports and must belong to a VLAN unique for each customer.
For more information about tunnel ports, see
Tunneling."
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. Only one SVI can be associated with a VLAN, but you need to configure
an SVI for a VLAN only when you wish to route between VLANs, fallback-bridge nonroutable protocols
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. In Layer 2 mode, SVIs provide IP host connectivity only to the system; in Layer 3 mode,
you can configure routing across SVIs.
SVIs are created the first time that you enter the vlan interface configuration command for a VLAN
interface. The VLAN corresponds to the VLAN tag associated with data frames on an ISL or 802.1Q
encapsulated trunk or the VLAN ID configured for an access port. Configure a VLAN interface for each
VLAN for which you want to route traffic, and assign it an IP address. For more information, see the
"Configuring IP Addressing on Layer 3 Interfaces" section on page
When you create an SVI, it does not become active until it is associated with a physical port.
Note
SVIs support routing protocols and bridging configurations. For more information about configuring IP
routing, see
Routing,"and
The standard multilayer software image (SMI) supports static routing and the Routing Information
Note
Protocol (RIP). To use SVIs for full Layer 3 routing or for fallback bridging, you must have the enhanced
multilayer software image (EMI) installed on your switch.
Routed Ports
A routed port is a physical port that acts like a port on a router; it does not have to be connected to a
router. A routed port is not associated with a particular VLAN, as is an access port. A routed port behaves
like a regular router interface, except that it does not support VLAN subinterfaces. Routed ports can be
configured with a Layer 3 routing protocol.
Catalyst 3550 Multilayer Switch Software Configuration Guide
10-4
Chapter 31, "Configuring IP Unicast Routing," Chapter 34, "Configuring IP Multicast
Chapter 36, "Configuring Fallback Bridging."
Chapter 10
Chapter 15, "Configuring 802.1Q and Layer 2 Protocol
31-4.
Configuring Interface Characteristics
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