H3C Technologies H3C S12500-X Series Switches - Manual (Page 12)

5
The VTEP uses the following processes to forward traffic at Layer 2:
• Unicast process—Applies to destination-known unicast traffic.
• Flood process—Applies to multicast, broadcast, and unknown unicast traffic.
When the VTEP forwards VXLAN traffic, it processes the 802.1q tag in the inner Ethernet header
depending on the VSI access mode (VLAN or Ethernet mode). In VLAN access mode, sites can use
different VLANs to provide the same service. For more information, see "
Access modes of VSIs ."
Unicast
The following process (see Figure 4 ) applies to a known unicast frame between sites:
1. The source VTEP encapsulates the Ethernet frame in the VXLAN/UDP/IP header.
In the outer IP header, the source IP address is the source VTEP's VXLAN tunnel source IP address.
The destination IP address is the VXLAN tunnel destination IP address.
2. The source VTEP forwards the encapsulated packet out of the outgoing VXLAN tunnel interface
found in the VSI's MAC address table.
3. The intermediate transport devices (P devices) forward the frame to the destination VTEP by using
the outer IP header.
4. The destination VTEP removes the headers on top of the inner Ethernet frame. It then performs MAC
address table lookup in the VXLAN's VSI to forward the frame out of the matching outgoing
interface.
Figure 4 Inter-site unicast
Flood
The VTEP floods a broadcast, multicast, or unknown unicast frame to all site-facing interfaces and VXLAN
tunnels in the VXLAN, except for the incoming interface.
VXLAN supports the following modes for flood traffic:
• Unicast mode—Also called head-end replication. The source VTEP replicates the flood frame, and
then sends one replica to the destination IP address of each VXLAN tunnel in the VXLAN. See Figure
5 .
VTEP 1 VTEP 2
Transport network
P
Server 1
VM 1
VM 2
VM 3
Server 3
VM 7
VM 8
VM 9
MAC Table on VTEP 1
VXLAN/VSI MAC Interface
VXLAN 10/VSI A MAC 1 FGE1/0/1, VLAN 2
VXLAN 10/VSI A MAC 7 Tunnel 1
Server 2
VM 4
VM 5
VM 6
FGE1/0/1
FGE1/0/2
MAC Table on VTEP 2
VXLAN/VSI MAC Interface
VXLAN 10/VSI A MAC 1 Tunnel 1
VXLAN 10/VSI A MAC 7 FGE1/0/1, VLAN 20
FGE1/0/1
VXLAN tunnel 1