VXLAN Encapsulation and its Frame FormatBy Mohammed Umair

VXLAN Frame Format A Native/Original Ethernet frame will be

encapsulated with four Header. VXLAN Header is a 8 byte field that has1) Flags (8 bits): I Flag is 1 bit, set to 1 for Valid VNI,

rest 7 bits are reserved2) VXLAN Network Identifier: is a 24 bit value used

to designate the individual VXLAN overlay network on which the communicating VMs are situated.

3) Reserved fields (24 bit and 8 bit): must be set to 0

VXLAN Frame Format Contd… Outer UDP Header: Outer UDP Header with a

Source Port provided by the VTEP and the Destination Port being a well known Port Assigned by IANA

1) Destination Port : IANA has assigned Destination Port number 4789 for VXLAN

2) Source Port: It is recommended that the UDP Source port be calculated using Hash of fields from the inner packet. It is recommended that the value be in the range between 49152-65535

3) UDP Checksum

VXLAN Frame Format Contd… Outer IP Header: Having Source IP and

Destination IP Address.1) Source IP Address: Source IP Address indicates

the IP Address of the VTEP over which the communicating VM is running or communicating VM is connected to.

2) Destination IP Address: The Destination IP Address can be Unicast or Multicast IP Address. Unicast IP Address indicates the Destination VTEP IP. Multicast IP is used when Multicast routing is used for VXLAN Signaling.

VXLAN Frame Format Contd… Outer Ethernet Header 1) Outer Destination MAC Address: This

Address can be of Target VTEP or of an intermediate Layer 3 router.

2) Outer Source MAC Address: This Address is MAC address of the Tunnel Source VTEP.

3) Outer VLAN Tag is optional.

Outer Ethernet HeaderOuter Destination MAC Address

Outer Destination MAC Address

Outer Source MAC Address

Outer Source MAC Address

Optional Ethtype = C-TAG 802.1Q

Outer.VLAN Tag Information

Ethertype = 0x0800 (for IPV4)

Ethertype = 0x86DD (for IPV6)

Outer IPV4 HeaderVersio

n

Header

LengthTOS Or DiffServ Total Length

Identifier FLAGS

Fragment Offset

TTL Protocol=17(UDP)

Header Checksum

Outer Source IPV4 Address

Outer Destination IPV4 Address

Outer IPV6 Header (if IPV6 is used as underlay)Versio

nTraffic Class

Flow Label

Payload Length NxtHdr=17(UDP)

Hop Limit

Outer Source IPv6 Header

Outer Destination IPv6 Header

Outer UDP Header

Source Port Destination Port = VxLAN Port

UDP Length UDP Checksum

VXLAN Header

R R R R I R R R Reserved

VXLAN Network Identifier (VNI) Reserved

Inner (Native) Ethernet HeaderInner Destination MAC Address

Inner Destination MAC Address

Inner Source MAC Address

Inner Source MAC Address

Optional Ethtype = C-TAG 802.1Q

Inner.VLAN Tag Information

Payload Ethertype of Original Payload

Original Ethernet Payload (FCS of original Ethernet Frame Not Included)

Frame Check Sequence

New FCS (Frame Check Sequence) for Outer Ethernet Frame

Sample Frame with VxLAN Header

Thank You