VXLAN is a network virtualization technique that performs MAC-in-UDP encapsulation by adding a UDP header and a VXLAN header before an original Ethernet packet. Figure1 shows the VXLAN packet format.
Figure 1-5 VXLAN packet format![]()
Table 1-2 Fields in the VXLAN packet formatField
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Description
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VXLAN header
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- VXLAN Flags (8 bits): The value is 00001000.
- VNI (24 bits): VXLAN Segment ID or VXLAN Network Identifier used to identify a VXLAN segment.
- Reserved fields (24 bits and 8 bits): must be set to 0.
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Outer UDP header
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- DestPort: destination port number, which is 4789 for UDP.
- Source Port: source port number, which is calculated by performing the hash operation on the inner Ethernet frame headers.
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Outer IP header
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- IP SA: source IP address, which is the IP address of the local VTEP of a VXLAN tunnel.
- IP DA: destination IP address, which is the IP address of the remote VTEP of a VXLAN tunnel.
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Outer Ethernet header
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- MAC DA: destination MAC address, which is the MAC address mapped to the next-hop IP address based on the destination VTEP address in the routing table of the VTEP on which the VM that sends packets resides.
- MAC SA: source MAC address, which is the MAC address of the VTEP on which the VM that sends packet resides.
- 802.1Q Tag: VLAN tag carried in packets. This field is optional.
- Ethernet Type: Ethernet packet type. The value is 0x0800 in IP packets.
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