VLAN termination application scenarios

Inter-VLAN communication

Hosts in different VLANs cannot directly communicate with each other. You can use Layer 3 routing to allow all VLANs to communicate. To restrict communication to the specified VLANs, configure VLAN termination on subinterfaces.

As shown in Figure 1, Host A and Host B are in different VLANs. The two hosts can communicate with each other after you perform the following tasks:

  1. Specify 1.1.1.1/24 and 1.1.2.1/24 as the gateway IP addresses for Host A and Host B, respectively.

  2. On the device, configure VLAN termination on Layer 3 Ethernet subinterfaces GigabitEthernet 1/0/1.1 and GigabitEthernet 1/0/2.1.

Figure 1: VLAN termination for inter-VLAN communication

LAN-WAN communication

Typically, WAN protocols such as ATM, Frame Relay, and PPP do not recognize VLAN-tagged packets from LANs. Before packets are sent to a WAN, the sending port must locally record the VLAN information and remove VLAN tags from the packets. To do that, configure VLAN termination on subinterfaces.

As shown in Figure 2, a host is located on a customer network and wants to access the WAN network through a PPPoE connection. CVLAN and SVLAN represent the VLAN on the customer network and service provider network, respectively.

To access the WAN network, a packet originating from the host is processed as follows:

  1. Layer 2 Switch A adds a CVLAN tag to the packet and sends the packet.

  2. Layer 2 Switch B adds an SVLAN tag to the packet on the QinQ-enabled port.

  3. The packet is forwarded on the service provider network based on the SVLAN tag.

  4. The PPPoE gateway removes the two layers of VLAN tags from the packet and adds new VLAN tags on the QinQ termination-enabled port.

  5. The PPPoE gateway sends the packet to the WAN network through synchronous/asynchronous serial interface Serial 2/1/0.

Figure 2: VLAN termination enables LAN-WAN communication