ccie certification cost A brief look at vxlan technology (1)
VXLAN is transmitted by encapsulating data frames communicated in a logical network in a physical network. Ccie certification cost .The process of encapsulation and decapsulation is performed by a VTEP node. After VXLAN adds the data frame in the logical network to the VXLAN header, it is encapsulated in the UDP packet in the physical network.
• Outer MAC Header: Encapsulates the outer Ethernet header, 14 bytes, or 18 bytes if there is a VLAN TAG. The source MAC address is the MAC address of the VTEP to which the source VM belongs, and the destination MAC address is the MAC address of the next hop device on the path to the destination VTEP. The type field is 0x0800, indicating that the inner layer encapsulates an IP packet.Ccie certification cost .
• Outer IP Header: Encapsulates the outer IP header, 20 bytes. The source IP address is the IP address of the VTEP to which the source VM belongs, and the destination IP address is the IP address of the VTEP to which the destination VM belongs. Ccie certification cost .The protocol field is 0x11, indicating that the inner layer encapsulates UDP packets.
• UDP Header: UDP header, 8 bytes. The UDP destination port number is fixed to 4789, indicating that the inner layer encapsulated packet is a VXLAN packet. Ccie certification cost .The UDP source port number is a random arbitrary value and can be used for multipath load sharing between VTEPs.
• VXLAN Header: VXLAN header newly defined by the VXLAN protocol, 8 bytes
• Flags: 8 bits, RRRRIRRR. When the “I” bit is 1, it indicates that the VXLAN ID in the VXLAN header is valid; when it is 0, it indicates that the VXLAN ID is invalid. The “R” bit is left unused and is set to 0.
• VXLAN ID (VNI): 24 bit, used to identify a separate VXLAN network.
• Reserved: 24 bit and 8 bit, respectively. Reserved bit.
• Original L2 Frame: Original Ethernet telegram.
As shown in the packet encapsulation, the VXLAN header and the original Layer 2 packet exist as payloads of UDP packets. The network device between the VTEPs needs to be forwarded according to the Outer MAC Header and the Outer IP Header. The UDP Source Port is used for load balancing. This process is identical to forwarding ordinary IP packets. In this way, in addition to the VTEP device, a large number of devices on the live network can support the VXLAN network without replacement or upgrade.
However, the newly added VXLAN message encapsulation also introduces a problem, that is, the setting of the MTU value.
Generally, the default MTU of a virtual machine is 1500 Bytes, which means that the original Ethernet packet is up to 1500 bytes. When this message passes VTEP, it will encapsulate a new 50-byte header (VXLAN header 8 bytes + UDP header 8 bytes + external IP header 20 bytes + external MAC header 14 bytes), thus the entire message length reached 1550 bytes. On the existing VTEP device, the VXLAN packet cannot be fragmented when the VXLAN packet is decapsulated. Ccie certification cost .Otherwise, the packet cannot be decapsulated correctly. This requires that the MTU of all network devices between VTEPs be a minimum of 1550 bytes.
If the MTU value of the intermediate device is not convenient to change, then setting the virtual machine’s MTU value to 1450 can also solve this problem temporarily.
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Ccie certification cost A brief look at vxlan technology (1)
