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WLAN V200R008C10 Typical Configuration Examples

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Data Packet Processing

Data Packet Processing

Packets transmitted on a WLAN include management packets and service data packets. Management packets must be transmitted over Control and Provisioning of Wireless Access Points (CAPWAP) tunnels, and service data packets can be transmitted over CAPWAP tunnels, soft GRE tunnels, or directly.

Management packets transmit management data between an AC and AP. Data packets transmit data from STAs and the upper-layer network when WLAN users surf on the Internet.

On a WLAN, packets transmitted between STAs and APs are 802.11 packets. APs are bridges between STAs and the upper layer wired network. They convert 802.11 packets into 802.3 packets and forward 802.3 packets to the wired network.

Management packets and service data packets are marked with different VLAN tags on a WLAN.The following describes the forwarding process of management and service data packets. Here, VLAN m and VLAN m' represent management VLANs, while VLAN s and VLAN s' represent service VLANs.
  • When an AP connects to an AC through a Layer 2 network, VLAN m is the same as VLAN m', and VLAN s is the same as VLAN s'.
  • When an AP connects to an AC through a Layer 3 network, VLAN m is different from VLAN m', and VLAN s is different from VLAN s'.

WLAN roaming is categorized as Layer 2 and Layer 3 roaming depending on whether a STA roams within the same subnet. In roaming scenarios, management packets are forwarded through the CAPWAP tunnel, while service data packets can be forwarded through the CAPWAP tunnel or using direct forwarding mode.

Management Packet Forwarding Process

As shown in Figure 3-5:
  • In the uplink direction (from the AP to the AC): When receiving management packets, the AP encapsulates the packets in CAPWAP packets. The switch tags the packets with VLAN m. The AC decapsulates the CAPWAP packets and removes the tag VLAN m'.
  • In the downlink direction (from the AC to the AP): When receiving downstream management packets, the AC encapsulates the packets in CAPWAP packets and tags them with VLAN m'. The switch removes VLAN m from the packets. The AP decapsulates the CAPWAP packets.

The devices between an AC and AP must be configured to allow VLAN m and transparently transmit packets of VLAN m.

Figure 3-5 Management packet forwarding

Direct Forwarding of Service Data Packets

Figure 3-6 shows the direct forwarding process of service data packets. In direct forwarding mode, service data packets are not encapsulated with CAPWAP.
  • In the uplink direction (from the STA to the Internet): When upstream service data packets in 802.11 format are sent from the STA to the AP, the AP converts the packets into 802.3 packets, tags the packets with VLAN s, and forwards the packets to the destination.
  • In the downlink direction (from the Internet to the STA): When downstream service data packets in 802.3 format reach the AP (the packets are tagged with VLAN s' by upstream devices), the AP converts the 802.3 packets into 802.11 packets and forwards them to the STA.

The devices between an AC and AP must be configured to allow service VLAN s and transparently transmit packets of VLAN s.

In direct forwarding mode, an AC is connected to a core or aggregation switch in bypass mode. The AC does not forward service data and only manages APs. If an AC is connected to an upstream switch in inline mode, the AC forwards data packets. In this networking, the AC acts as an aggregation switch.

Figure 3-6 Direct forwarding of service data packets

Forwarding Service Data Packets over a CAPWAP Tunnel

In tunnel forwarding mode, APs set up control tunnels and data tunnels with an AC. Data packets of WLAN users and management packets are encapsulated in CAPWAP data packets and control packets, and forwarded over the CAPWAP tunnels. As shown in Figure 3-7:
  • In the uplink direction (from the STA to the Internet): When upstream service data packets in 802.11 format are sent from the STA to the AP, the AP converts the packets into 802.3 packets, tags the packets with VLAN s, and encapsulates them in CAPWAP packets. The upstream switch tags the packets with VLAN m. The AC decapsulates the CAPWAP packets and removes the tag VLAN m' from the packets.
  • In the downlink direction (from the Internet to the STA): When downstream service data packets reach the AC, the AC encapsulates the packets in CAPWAP packets, allows the packets carrying VLAN s to pass through, and tags the packets with VLAN m'. The switch removes VLAN m from the packets. The AP decapsulates the CAPWAP packets, removes VLAN s, converts the 802.3 packets into 802.11 packets, and forwards them to the STA.

Management VLAN tag VLAN m is the outer tag of CAPWAP-encapsulated packets. The intermediate devices between the AC and AP can only transparently transmit packets carrying VLAN m and cannot be configured with VLAN s encapsulated in the CAPWAP packets.

All encapsulated data packets are processed and forwarded by the AC, regardless of whether the AC is connected to the upstream switch in inline or bypass mode.

Figure 3-7 Forwarding service data packets over a CAPWAP tunnel

Forwarding Service Data Packets over a Soft GRE Tunnel

As shown in Figure 3-8, service data packets can be transmitted over a soft GRE tunnel.
  • When receiving upstream service data packets in 802.11 format from the STA, the AP converts the packets into 802.3 packets, encapsulates the packets into a soft GRE tunnel, and forwards the packets to the BRAS. The BRAS decapsulates the packets and implements unified accounting and authentication.
  • The BRAS encapsulates downlink service data packets into a soft GRE tunnel and forwards the packets to the AP. The AP then decapsulates the packets, converts the packets into 802.11 packets, and sends them to the STA.

The route between the AP and BRAS must be reachable so that service data packets can be transmitted properly over the soft GRE tunnel.

Figure 3-8 Forwarding service data packets over a soft GRE tunnel

Forwarding Service Data Packets During Layer 2 Roaming

As shown in Figure 3-9, during Layer 2 roaming, the STA stays within the same subnet. The FAP/FAC processes packets of a Layer 2 roaming STA in the same way as it processes packets of a newly online STA. The FAP/FAC forwards the packets on the local network but not send the packets back to the HAP/HAC over the inter-AC tunnel.
  • Before roaming: When receiving upstream service data packets from a STA, the HAP forwards the packets to the HAC. The HAC then directly forwards the packets to the destination. When receiving downstream service data packets from the HAC, the HAP forwards the packets to the STA.
  • After roaming: When receiving upstream service data packets from a STA, the FAP forwards the packets to the FAC. The FAC then directly forwards the packets to the destination. When receiving downstream service data packets from the FAC, the FAP forwards the packets to the STA.
Figure 3-9 Forwarding service data packets during Layer 2 roaming

Forwarding Service Data Packets During Layer 3 Roaming

The STA stays in different subnets before and after Layer 3 roaming. To ensure that the STA can still access the original network after roaming, user traffic is forwarded to the original subnet over tunnels.

  • As shown in Figure 3-10, in tunnel forwarding mode, service packets exchanged between the HAP and HAC are encapsulated through a CAPWAP tunnel, and the HAP and HAC can be considered in the same subnet. Instead of forwarding the packets back to the HAP, the HAC directly forwards the packets to the upper-layer network.
    Figure 3-10 Tunnel forwarding of service data packets during Layer 3 roaming

    Service Data Packet Type

    Before Roaming

    After Roaming

    Upstream service data

    1. The STA sends a service packet to the HAP.
    2. After receiving the service packet, the HAP sends it to the HAC.
    3. The HAC forwards the service packet to the upper-layer network.
    1. The STA sends a service packet to the FAP.
    2. After receiving the service packet, the FAP sends it to the FAC.
    3. The FAC forwards the service packet to the HAC through a tunnel between them.
    4. The HAC forwards the service packet to the upper-layer network.

    Downstream service data

    1. The HAC encapsulates downstream service data in a CAPWAP packet, and sends it to the HAP.
    2. The HAP receives the CAPWAP packet and decapsulates it.
    3. The HAP sends the service packet to the STA.
    1. The HAC encapsulates downstream service data in a CAPWAP packet.
    2. The HAC forwards the service packet to the FAC through a tunnel between them.
    3. The FAP receives the CAPWAP packet and decapsulates it.
    4. The FAP sends the service packet to the STA.
  • As shown in Figure 3-11, in direct forwarding mode, service packets exchanged between the HAP and HAC are not encapsulated through the CAPWAP tunnel; therefore, whether the HAP and HAC reside in the same subnet is unknown. Packets are forwarded back to the HAP by default. If the HAP and HAC are located in the same subnet, configure the HAC with higher performance as the home agent. This reduces the load on the HAP and improves the forwarding efficiency.
    Figure 3-11 Direct forwarding of service data packets during Layer 3 roaming

    Service Data Packet Type

    Before Roaming

    After Roaming

    Configuring the AC as the Home Agent

    Upstream service data

    1. The STA sends a service packet to the HAP.
    2. After receiving the service packet, the HAP forwards the service packet to the upper-layer network directly.
    1. The STA sends a service packet to the FAP.
    2. After receiving the service packet, the FAP sends it to the FAC over the CAPWAP tunnel.
    3. The FAC forwards the service packet to the HAC through a tunnel between them.
    4. The HAC sends the service packet to the HAP over the CAPWAP tunnel.
    5. The HAP forwards the service packet to the upper-layer network.
    1. The STA sends a service packet to the FAP.
    2. After receiving the service packet, the FAP sends it to the FAC over the CAPWAP tunnel.
    3. The FAC forwards the service packet to the HAC through a tunnel between them.
    4. The HAC forwards the service packet to the upper-layer network.

    Downstream service data

    1. The upper-layer network sends a service packet to the HAC.
    2. The HAC sends the service packet to the HAP.
    3. After receiving the service packet, the HAP sends it to the STA.
    1. The upper-layer network sends a service packet to the HAP.
    2. The HAP sends the service packet to the HAC over the CAPWAP tunnel.
    3. The HAC forwards the service packet to the FAC through a tunnel between them.
    4. After receiving the service packet, the FAC sends it to the FAP over the CAPWAP tunnel.
    5. The FAP sends the service packet to the STA.
    1. The upper-layer network sends a service packet to the HAC.
    2. The HAC forwards the service packet to the FAC through a tunnel between them.
    3. After receiving the service packet, the FAC sends it to the FAP over the CAPWAP tunnel.
    4. The FAP sends the service packet to the STA.
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Updated: 2019-03-30

Document ID: EDOC1000184389

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