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NE40E-M2 V800R010C10SPC500 Feature Description - LAN Access and MAN Access 01

This is NE40E-M2 V800R010C10SPC500 Feature Description - LAN Access and MAN Access
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How BPDU Tunneling Works

How BPDU Tunneling Works

To implement the transparent transmission, the following conditions must be met:

  • Branches of a user network can exchange BPDUs.

  • BPDUs sent from a user network cannot be processed by the carrier network devices.

  • BPDUs from different user networks must be isolated and free from interference.

Configuring BPDU tunneling on carrier network devices meets the preceding conditions. After BPDU tunneling is configured, the carrier network can transparently transmit BPDUs between user networks through BPDU tunnels.

The NE40E supports the following BPDU tunneling based on implementation modes:

  • Interface-based BPDU tunneling

  • VLAN-based BPDU tunneling (VLAN is short for virtual local area network.)

  • QinQ-based BPDU tunneling (QinQ is short for 802.1Q in 802.1Q.)

Interface-based BPDU Tunneling

Figure 14-3 Interface-based BPDU tunneling

As shown in Figure 14-3, each interface on a provider edge (PE) is connected to one user network. The user networks belong to different local area networks (LANs); specifically, LAN A and LAN B. BPDUs sent from the user networks to the PEs are untagged. However, the PEs need to identify the LANs to which the BPDUs belong, because BPDUs from a user network in LAN A must be forwarded to other user networks in LAN A, rather than user networks in LAN B. In addition, BPDUs sent from user networks must not be processed by the central processing units (CPUs) of the PEs on the carrier network.

Interface-based BPDU tunneling can resolve the preceding problem. One method for implementing interface-based BPDU tunneling is to configure different roles for devices.

  1. Configure the devices on the carrier network as providers. The well-known destination Media Access Control (MAC) address of BPDUs sent by the devices on the carrier network is changed to 0180-C200-0008.

  2. Configure the devices on user networks as customers. The well-known destination MAC address of BPDUs sent by the devices on the user networks remains 0180-C200-0000.

  3. Add the interfaces connected to each LAN's user networks to the same VLAN. After receiving BPDUs from user networks, the PEs add VLAN IDs to the BPDUs based on the port default VLAN ID (PVID) of each interface.

  4. Configure the PE interfaces that are connected to the CEs to allow BPDUs with specified VLAN IDs to pass. The PEs (providers) do not send the BPDUs received from user networks to their CPUs for processing, because the well-known destination MAC address of these BPDUs is 0180-C200-0000, which is different than that sent by the carrier network devices. Instead, when an interface of a PE receives BPDUs from a user network, the PE forwards them through a BPDU tunnel selected based on the PVID of the interface.

    In this manner, BPDUs can be transparently transmitted over the Layer 2 network of the carrier network.

As shown in Figure 14-3, when a PE receives a BPDU from a user network, the PE adds a VLAN ID to the BPDU based on the PVID of the interface, selects a BPDU tunnel based on the VLAN ID, and transmits the BPDU through the tunnel. BPDUs of LAN A are transmitted through the BPDU tunnel with the VLAN ID 300, and BPDUs of LAN B are transmitted through the BPDU tunnel with the VLAN ID 200.

The other method for implementing interface-based BPDU tunneling is to configure the same role for devices. Specifically, configure the devices on both the carrier and user networks as customers. This method is similar to the preceding method, except for the following: You need to configure the carrier network devices to change the well-know destination MAC address of BPDUs sent from user networks to a specific multicast MAC address. Then you need to enable BPDU tunneling on the carrier network devices' interfaces that are connected to the user network devices.

VLAN-based BPDU Tunneling

Figure 14-4 VLAN-based BPDU tunneling

In most cases, PEs function as aggregation devices. As shown in Figure 14-4, the interface on PE1 can receive BPDUs from both LAN A and LAN B. To differentiate BPDUs from these LANs, the CEs add VLAN tags to the BPDUs before sending them to the PEs. BPDUs from LAN A carry the VLAN ID 200, and BPDUs from LAN B carry the VLAN ID 100.

BPDUs sent by the Rapid Spanning Tree Protocol (RSTP) or Multiple Spanning Tree Protocol (MSTP) are not encapsulated with tags. If VLAN-based BPDU tunneling is not enabled on a PE, the PE considers the received tagged BPDUs as error packets and discards them. If VLAN-based BPDU tunneling is enabled on a PE, the PE does not send the received tagged BPDUs to its CPU for processing. Instead, the PE transparently transmits the BPDUs through the BPDU tunnel to another user network.

One method for implementing VLAN-based BPDU tunneling is to configure different roles for devices.

  1. Configure the devices on the carrier network as providers. The well-known destination MAC address of BPDUs sent by the devices on the carrier network is changed to 0180-C200-0008.

  2. Configure the devices on user networks as customers. The well-known destination MAC address of BPDUs sent by the devices on the user networks remains 0180-C200-0000.

  3. Configure the CEs to add specified VLAN IDs to BPDUs before sending them to the PEs.

  4. Configure the PE interfaces that are connected to the CEs to allow BPDUs with specified VLAN IDs to pass. The PEs (providers) do not send the BPDUs received from user networks to their CPUs for processing, because the well-known destination MAC address of these BPDUs is 0180-C200-0000, which is different than that sent by the carrier network devices. Instead, when an interface of a PE receives BPDUs from a user network, the PE forwards them through BPDU tunnels selected based on the VLAN IDs carried by the BPDUs.

    In this manner, BPDUs can be transparently transmitted over the Layer 2 network of the carrier network.

As shown in Figure 14-4, BPDUs sent from LAN A carry the VLAN ID 200. PE1 allows the BPDUs with the VLAN ID 200 to be transparently transmitted over the carrier network through the BPDU tunnel with the VLAN ID 200. PE2 then forwards these BPDUs with the VLAN ID 200 to LAN A to perform the spanning tree calculation.

BPDUs sent from LAN B carry the VLAN ID 100. PE1 allows the BPDUs with the VLAN ID 100 to be transparently transmitted over the carrier network through the BPDU tunnel with the VLAN ID 100. PE2 then forwards these BPDUs with the VLAN ID 100 to LAN B to perform the spanning tree calculation.

The other method for implementing VLAN-based BPDU tunneling is to configure the same role for devices. Specifically, configure the devices on both the carrier and user networks as customers. This method is similar to the preceding method, except for the following: You need to configure the carrier network devices to change the well-know destination MAC address of BPDUs sent from user networks to a specific multicast MAC address. Then you need to enable BPDU tunneling on the carrier network devices' interfaces that are connected to the user network devices.

QinQ-based BPDU Tunneling

  • QinQ overview

    The QinQ protocol is a Layer 2 tunneling protocol based on the IEEE 802.1Q standard. QinQ improves the utilization of VLANs by adding another 802.1Q tag to a packet already carrying one. This 802.1Q tag addition enables services from private VLANs to be transparently transmitted over the public network. QinQ gains its name because packets transmitted on the backbone network carry two 802.1Q tags: a public VLAN tag (outer tag) and a private VLAN tag (inner tag).

    Figure 14-5 shows the QinQ packet format. A QinQ packet contains a public VLAN tag following the SA (source address) field, while an 802.1Q packet does not contain this tag.

    NOTE:

    The QinQ function configured on a Layer 2 interface is also called VLAN stacking.

    Figure 14-5 802.1Q encapsulation and QinQ encapsulation

  • QinQ-based BPDU tunneling

    Figure 14-6 QinQ-based BPDU tunneling

    When many user networks are connected to the carrier network, VLAN-based transparent transmission of BPDUs requires a large number of VLAN IDs of the carrier network. This may result in a shortage of public VLAN ID resources. In this situation, QinQ-based BPDU tunnels can be used to transmit BPDUs over the carrier network.

    As shown in Figure 14-6, QinQ-based BPDU tunneling is configured on the PE interfaces, and these interfaces allocate different outer VLAN tags to BPDUs based on their CE VLAN IDs (inner VLAN IDs).

    The method for configuring QinQ-based BPDU tunneling is as follows:

    1. Add to VLANs the CE interfaces that are connected to the PEs, and configure the interfaces to add VLAN tags to BPDUs before sending them to the PEs.

    2. Enable BPDU tunneling and QinQ on the inbound interfaces of the PEs on the carrier network.

    3. Configure the aggregate inbound interfaces of the PEs to allocate outer VLAN tags to BPDUs based on their CE VLAN IDs. The PEs select different BPDU tunnels to transmit the BPDUs based on their outer VLAN IDs over the carrier network.

    4. Enable BPDU tunneling and QinQ on the outbound interfaces of the PEs on the carrier network.

    5. Configure the aggregate outbound interfaces of the PEs to strip the outer VLAN tags of the BPDUs and transmit them to user networks based on their inner VLAN IDs.

    As shown in Figure 14-6, when a PE receives BPDUs with the CE VLAN IDs 100 to 199, the PE adds the outer VLAN ID 20 to the BPDUs and transmits them over the carrier network; when a PE receives BPDUs with the CE VLAN IDs 200 to 299, the PE adds the outer VLAN ID 30 to the BPDUs and transmits them over the carrier network. In this manner, BPDUs from different user networks are transparently transmitted over the carrier network, and VLAN ID resources are saved for the carrier network.

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Updated: 2019-01-02

Document ID: EDOC1100058405

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