Connectivity Guide

Figure 156. VXLAN Frame Format
Components of VXLAN Frame Format
Some of the important fields of the VXLAN frame format are described below:
Outer Ethernet
Header:
The Outer Ethernet Header consists of the following components:
● Destination Address: Generally, it is a first hop router's MAC address when the VTEP is on a
different address.
● Source Address : It is the source MAC address of the router that routes the packet.
● VLAN: It is optional in a VXLAN implementation and will be designated by an ethertype of 0×8100 and
has an associated VLAN ID tag.
● Ethertype: It is set to 0×0800 because the payload packet is an IPv4 packet. The initial VXLAN draft
does not include an IPv6 implementation, but it is planned for the next draft.
Outer IP Header: The Outer IP Header consists of the following components:
● Protocol: It is set to 0×11 to indicate that the frame contains a UDP packet .
● Source IP: It is the IP address of originating VTEP.
● Destination IP: : It is the IP address of target VTEP.
Outer UDP
Header:
The Outer UDP Header consists of the following components:
● Source Port: Entropy of the inner frame. The entropy could be based on the Inner L2 header or Inner
L3 header.
● VXLAN Port : IANA-assigned VXLAN Port (4789).
● UDP Checksum: The UDP checksum field is transmitted as zero. When a packet is received with a
UDP checksum of zero, it is accepted for decapsulation.
VXLAN Header :
● VXLAN Flags : Reserved bits set to zero except bit 3, the first bit, which is set to 1 for a valid VNI
● VNI: The 24-bit field that is the VXLAN Network Identifier
● Reserved: A set of fields, 24 bits and 8 bits, that are reserved and set to zero .
Frame Check
Sequence (FCS):
Note that the original Ethernet frame's FCS is not included, but new FCS is generated on the outer
Ethernet frame.
Limitations on VXLAN
While configuring a VXLAN, the following conditions apply:
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Virtual Extensible LAN (VXLAN)