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Cisco Nexus 1000V Troubleshooting Guide, Release 5.2(1)SV3(1.1)
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Chapter 25 VXLANs
Information About VXLANs
scope the MAC address of the payload frame. The VXLAN ID to which a VM belongs is indicated within
the port profile configuration of the vNIC and is applied when the VM connects to the network. A
VXLAN supports three different modes for broadcast, multicast, and MAC distribution mode transport:
•
Multicast Mode—A VXLAN uses an IP multicast network to send broadcast, multicast, and
unknown unicast flood frames. When a VM joins a VXLAN segment, the server joins a multicast
group. Broadcast traffic from the VM is encapsulated and is sent using the multicast outer
destination IP address to all the servers in the same multicast group. Subsequent unicast packets are
encapsulated and unicast directly to the destination server without a multicast IP address.
•
Unicast-only Mode—A VXLAN uses each VEM's single unicast IP address as the destination IP
address to send broadcast, multicast, and unknown unicast flood frames. Broadcast traffic from the
VM is replicated to each VEM by encapsulating it with a VXLAN header and the designated IP
address as the outer destination IP address.
•
MAC Distribution Mode (supported only in unicast mode)—In this mode, the unknown unicast
flooding is reduced because the Virtual Supervisor Module (VSM) learns all the MAC addresses
from the VEMs in all VXLANs and distributes those MAC addresses with VXLAN Tunnel Endpoint
(VTEP) IP mappings to other VEMs.
The VXLAN creates LAN segments by using an overlay approach with MAC in IP encapsulation.
VXLAN Tunnel EndPoint
Each VEM requires at least one IP/MAC pair to terminate VXLAN packets. This IP/MAC address pair
is known as the VXLAN Tunnel End Point (VTEP) IP/MAC addresses. The VEM supports IPv4
addressing for this purpose. The IP/MAC address that the VTEP uses is configured when you enter the
capability vxlan
command. You can have a maximum of four VTEPs in a single VEM.
One VTEP per VXLAN segment is designated to receive all broadcast, multicast, and unknown unicast
flood traffic for the VEM.
When encapsulated traffic is destined to a VEM that is connected to a different subnet, the VEM does
not use the VMware host routing table. Instead, the VTEPs initiate the Address Resolution Protocol
(ARP) for remote VEM IP addresses. If the VTEPs in the different VEMs are in different subnets, you
must configure the upstream router to respond by using the Proxy ARP.
VXLAN Gateway
VXLAN termination (encapsulation and decapsulation) is supported on virtual switches. As a result, the
only endpoints that can connect into VXLANs are VMs that are connected to a virtual switch. Physical
servers cannot be in VXLANs and routers or services that have traditional VLAN interfaces cannot be
used by VXLAN networks. The only way that VXLANs can currently interconnect with traditional
VLANs is through VM-based software routers.
Note
Starting with Release 5.2(1)SV3(1.15), Cisco Nexus 1000V for VMware vSphere does not support the
VXLAN Gateway feature.