How to configure VXLAN Flood and Learn

Theory

VXLAN Flood and Learn is used to maintain a Layer 2 network over a Layer 3 network. The switches run a NVE interface also called VTEP that is used to encapsulate the original frame in a UDP packet and flood it along a multicast tree. The other switches that participate in the same multicast tree will decapsulate the packet and flood it out of their local ports based on the Vlan.

• 1. SRV1 sends ARP to discover SRV2
• 2. VTEP1 looksup the VLAN to VNI mapping and encapsalutes the ARP inside the VXLAN VNI header
• 3. VTEP1 adds its NVE interface as Source IP and sends the packet to the multicast group of the VNID
• 4. VTEP2 receives the multicast and decapsulates the packet and floods it to the mapped VLAN of the VXLAN VNID
• 5. SRV2 gets the ARP and will send an ARP reply to SRV1
• 6. VTEP2 looksup the VLAN to VNI mapping and encapsulate the arp reply inside the VXLAN VNI header
• 7. VTEP2 use its NVE interface as Source IP and sends the packet to the IP of the NVE interface of VTEP1
• 8. LEAF1 gets the ARP reply, decapsulates the VXLAN header and switches the ARP reply to SRV1

Configuration

VTEP1

feature pim
feature vn-segment-vlan-based
feature nv overlay 

ip route 10.10.10.2/32 10.1.1.2
ip pim rp-address 10.10.10.1 group-list 224.0.0.0/4

int lo10
  ip add 10.10.10.1/32
  ip pim sparse-mode 

int e1/1
 no switchport
 no sh
 ip add 10.1.1.1/30
 ip pim sparse-mode

int e1/2
 switchport access vlan 10

vlan 10
 vn-segment 1000

interface nve1
  no shutdown
  source-interface loopback10
  member vni 1000 mcast-group 230.1.1.1 

VTEP2

feature pim
feature vn-segment-vlan-based
feature nv overlay 

ip route 10.10.10.1/32 10.1.1.1
ip pim rp-address 10.10.10.1 group-list 224.0.0.0/4

int lo10
  ip address 10.10.10.2/32
  ip pim sparse-mode 

int e1/1
 no switchport
 no sh
 ip add 10.1.1.2/30
 ip pim sparse-mode

int e1/2
 switchport access vlan 10

vlan 10
 vn-segment 1000

interface nve1
  no shutdown
  source-interface loopback10
  member vni 1000 mcast-group 230.1.1.1 

Debug Commands

show nve interface
show nve peers
show nve vni
show ip mroute 230.1.1.1
show ip pim neighbor

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