Cisco Systems 8540 Configuring 802.1Q Vlan Encapsulation, Routerconfig# bridge 2 protocol ieee

Chapter 4 Configuring Interfaces

Configuring 802.1Q VLAN Encapsulation

Example

The following example shows how to configure the interfaces for VLAN bridging with ISL encapsulation shown in Figure 4-2:

Router(config)# interface fastethernet 1/0/1.1

Router(config-subif)# encap isl 50

Router(config-subif)# bridge-group 1

Router(config-subif)#interface fastethernet 1/0/0

Router(config-if)# bridge-group 1

Router(config-if)# exit

Router(config)# bridge 1 protocol ieee

Router(config)# interface fastethernet 1/0/1.2

Router(config-subif)# encap isl 100

Router(config-subif)# bridge-group 2

Router(config-subif)#interface fastethernet 3/0/1

Router(config-subif)# bridge-group 2

Router(config-subif)# exit

Router(config)# bridge 2 protocol ieee

Router(config)# exit

Router# copy system:running-config nvram:startup-config

When configuring ISL with IP, you cannot configure IP addresses on a subinterface unless the VLANs are already configured (that is, you must have already entered the encapsulation isl or encapsulation dot1q command). That is not the case with IPX, however—you can configure IPX networks on a subinterface even when the VLANs have not been configured.

The maximum VLAN bridge group values are as follows:

•Maximum number of bridge groups: 64

•Maximum number of interfaces per bridge group: 128

•Maximum number of subinterfaces per system: 255

For a complete configuration example for VLANs with ISL encapsulation, see the “Catalyst 8540 CSR with ISL, VLAN, and BVI with GEC” section on page C-1.

To monitor the VLANs once they are configured, use the commands described in the “Monitoring VLAN Operation” section on page 4-12.

Configuring 802.1Q VLAN Encapsulation

The IEEE 802.1Q standard provides a method for secure bridging of data across a shared backbone. IEEE 802.1Q VLAN encapsulation uses an internal, or one level, packet tagging scheme to multiplex VLANs across a single physical link, while maintaining strict adherence to the individual VLAN domains.

On an IEEE 802.1Q trunk port, all transmitted and received frames are tagged except for those on the one VLAN configured as the PVID (port VLAN identifier) or native VLAN for the port. Frames on the native VLAN are always transmitted untagged and are normally received untagged.

The VLAN configuration example shown in Figure 4-3depicts the following:

•Fast Ethernet ports 1/0/0 and subinterface 1/0/1.1 on the switch router are in bridge group 1. They are part of native VLAN 1, which uses 802.1Q encapsulation.

•Fast Ethernet port 3/0/1 and subinterface 1/0/1.2 are in bridge group 2. They are part of VLAN 100, which uses 802.1Q encapsulation.

•Fast Ethernet port 1/0/1 is configured as an 802.1Q trunk.

	Layer 3 Switching Software Feature and Configuration Guide
4-10	78-6235-04, Cisco IOS Release 12.0(10)W5(18)