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Working mechanisms

In a VXLAN-DCI network, VTEPs use MAC address entries to perform Layer 2 forwarding for VXLANs, and EDs perform Layer 3 forwarding based on ARP entries.

As shown in Figure 22, a VSI interface uses the same IP address to provide gateway services for a VXLAN on different EDs. Local proxy ARP is enabled on the EDs.

Figure 22: VXLAN-DCI working mechanisms

Intra-VXLAN traffic forwarding between sites

As shown in Figure 22, the network uses the following process to forward traffic in a VXLAN between sites (for example, from VM 1 to VM 4 in VXLAN 10):

  1. VM 1 sends an ARP request to obtain the MAC address of VM 4.

  2. VTEP 1 learns the MAC address of VM 1 and floods the ARP request in VXLAN 10.

  3. ED 1 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP request.

    2. Creates an ARP entry for VM 1 and replies with the MAC address of VSI-interface 10 (the gateway interface for VXLAN 10). The ARP reply is sent to VTEP 1.

  4. VTEP 1 removes the VXLAN encapsulation of the ARP reply, learns the MAC address of ED 1, and forwards the ARP reply to VM 1.

  5. VM 1 creates an ARP entry for VM 4. The MAC address in the entry is the MAC address of VSI-interface 10 on ED 1.

  6. ED 1 replaces the sender MAC address of the request with the MAC address of VSI-interface 10 on ED 1, and then floods the request to the remote EDs in VXLAN 10.

  7. ED 2 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP request.

    2. Creates an ARP entry for VM 1. The entry contains VM 1's IP address (10.1.1.100), the MAC address of VSI-interface 10 on ED 1, and the incoming VXLAN-DCI tunnel interface.

    3. Replaces the sender MAC address of the request with the MAC address of VSI-interface 10 on ED 2, and then floods the request on all VXLAN tunnels of VXLAN 10.

  8. VTEP 2 removes the VXLAN encapsulation of the ARP request, learns the MAC address of ED 2, and floods the ARP request to the local site.

  9. VM 4 creates an ARP entry for VM 1, and then sends a reply to VTEP 2. The MAC address in the ARP entry is the MAC address of VSI-interface 10 on ED 2.

  10. VTEP 2 looks up the MAC address table and forwards the ARP reply to ED 2.

  11. ED 2 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP reply.

    2. Creates an ARP entry for VM 4

    3. Replaces the sender MAC address of the ARP reply with the MAC address of VSI-interface 10 on ED 2, and sends the reply to ED 1.

  12. ED 1 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP reply.

    2. Creates an ARP entry for VM 4. The entry contains VM 4's IP address (10.1.1.200), the MAC address of VSI-interface 10 on ED 2, and the incoming VXLAN-DCI tunnel interface.

  13. For subsequent traffic between VM 1 and VM 4, the VTEPs and EDs use their respective MAC address tables and ARP tables to make the forwarding decision.

Inter-VXLAN traffic forwarding between sites

As shown in Figure 22, the network uses the following process to forward traffic between VXLANs (for example, from VM 1 in VXLAN 10 to VM 5 in VXLAN 20):

  1. VM 1 sends an ARP request to obtain the MAC address of the gateway at 10.1.1.1.

  2. VTEP 1 learns the MAC address of VM 1 and floods the ARP request in VXLAN 10.

  3. ED 1 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP request.

    2. Creates an ARP entry for VM 1 and replies with the MAC address of VSI-interface 10 (the gateway interface for VXLAN 10). The ARP reply is sent to VTEP 1.

  4. VTEP 1 removes the VXLAN encapsulation of the ARP reply, learns the MAC address of ED 1, and forwards the ARP reply to VM 1.

  5. VM 1 creates an ARP entry for the gateway and sends the packet destined for VM 5 to VTEP 1.

  6. VTEP 1 looks up the MAC address table and forwards the packet to ED 1.

  7. ED 1 performs the following operations:

    1. Removes the VXLAN encapsulation of the packet and looks up the routing table based on the destination IP address.

    2. Sends an ARP request to the local VTEP and remote ED of VXLAN 20 to obtain the MAC address of VM 5. In the ARP request, the sender IP address is 20.1.1.1, and the sender MAC address is the MAC address of VSI-interface 20 on ED 1.

  8. ED 2 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP request.

    2. Replaces the sender MAC address of the request with the MAC address of VSI-interface 20 on ED 2, and then floods the request on all VXLAN tunnels of VXLAN 20.

  9. VTEP 2 removes the VXLAN encapsulation of the ARP request, learns the MAC address of ED 2, and floods the ARP request to the local site.

  10. VM 5 creates an ARP entry for ED 2 and sends a reply to VTEP 2. The MAC address in the ARP entry is the MAC address of VSI-interface 20 on ED 2.

  11. VTEP 2 looks up the MAC address table and forwards the ARP reply to ED 2.

  12. ED 2 performs the following operations:

    1. Removes the VXLAN encapsulation of the ARP reply.

    2. Creates an ARP entry for VM 5.

    3. Sends a gratuitous ARP packet to ED 1. In the packet, the sender and target IP address is 20.1.1.200, and the sender MAC address is the MAC address of VSI-interface 20 on ED 2.

  13. ED 1 performs the following operations:

    1. Removes the VXLAN encapsulation of the packet.

    2. Creates an ARP entry for VM 5. The entry contains VM 5's IP address (20.1.1.200), the MAC address of VSI-interface 20 on ED 2, and the incoming VXLAN-DCI tunnel interface.

  14. For subsequent traffic between VM 1 and VM 5, the VTEPs and EDs use their respective MAC address tables and ARP tables to make the forwarding decision.

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