Vxlan Flood And Learn - Cisco Nexus 7000 Series Configuration Manual

VXLAN Flood and Learn

• Utilization of available network paths in the underlying infrastructure.
There are two unicast modes in which VXLAN can run. They are Flood and Learn mode and MAC Distribution
mode.
VXLAN Flood and Learn
VXLAN is MAC in IP/UDP encapsulation technique with a 24-bit segment identifier in the form of a VXLAN
ID. The larger VXLAN ID allows LAN segments to scale to 16 million in a cloud network. In addition, the
IP/UDP encapsulation allows each LAN segment to be extended across existing Layer 3 network. Traditionally
with virtual VTEPS the only endpoints that can connect into VXLANs are physical or virtual connections.
Physical servers cannot be in the VXLAN network. Routers or services that have traditional VLAN interfaces
cannot be used by VXLAN-based networks.
The VXLAN flood and learn gateway feature provides solution to this problem.
VXLAN flood and learn gateway enables the following:
• Host learning on VTEPs based on flood and learn behaviour
• VTEPs join underlay IP multicast groups based on VNI 'membership'
• If VNI exists behind VTEP, the packet flow joins the corresponding IP multicast group in underlay
• ARP (and other broadcast / unknown unicast / multicast traffic) in a given VNI flooded to all interested
• Gateway functions centralised in VXLAN flood and learn
• Cisco Nexus 7000 / 7700 vPC pair with L2 + L3 VXLAN gateway capabilities
• vPC provides MAC state synchronization and active-active HSRP forwarding
• Redundant VTEPs share Anycast VTEP IP address in underlay
• VXLAN bridging occurs directly between VTEPs
VXLAN MAC Distribution
In VXLAN MAC Distribution mode, head-end replication is used to deliver broadcast and multicast frames
to the entire network. MAC learning based on data plane activity is not performed, instead the central control
functionality of the Nexus 1000V (virtual supervisor module (VSM)) is used to keep track of all MAC addresses
in the domain and send this information to the VTEPs on the system.
Cisco Nexus 7000 Series NX-OS VXLAN Configuration Guide
8
VXLAN uses a 24-bit segment ID, the VXLAN network identifier (VNID). This allows a maximum of
16 million VXLAN segments to coexist in the same administrative domain. (In comparison, traditional
VLANs use a 12-bit segment ID that can support a maximum of 4096 VLANs.)
VXLAN packets are transferred through the underlying network based on its Layer 3 header. It uses
equal-cost multipath (ECMP) routing and link aggregation protocols to use all available paths.
VTEPs
Overview