Dell EMC SmartFabric OS10 User Guide Release 10.5.0

Enable overlay routing between virtual networks

The previous sections describe how a VTEP switches traffic between hosts in the same L2 tenant segment on a virtual network, and transports traffic over an IP underlay fabric. This section describes how a VTEP enables hosts in different L2 segments belonging to the same tenant VRF to communicate with each other.

Each tenant is assigned a VRF and each virtual-network interface is assigned an IP subnet in the tenant VRF. The VTEP acts as the L3 gateway that routes traffic from one tenant subnet to another in the overlay before encapsulating it in the VXLAN header and transporting it over the IP underlay fabric.

To enable host traffic routing between virtual networks, configure an interface for each virtual network and associate it to a tenant VRF. Assign a unique IP address in the IP subnet range associated with the virtual network to each virtual-network interface on each VTEP.

To enable efficient traffic forwarding on a VTEP, OS10 supports distributed and centralized gateway routing. A distributed gateway means that multiple VTEPs act as the gateway router for a tenant subnet. The VTEP nearest to a host acts as its gateway router. To support seamless migration of hosts and virtual machines on different VTEPs, configure a common virtual IP address, known as an anycast IP address, on all VTEPs for each virtual network. Use this anycast IP address as the gateway IP address on VMs.

To support multiple tenants when each tenant has its own L2 segments, configure a different IP VRF for each tenant. All tenants share the same VXLAN underlay IP fabric in the default VRF.

1. Create a non-default VRF instance for overlay routing in Configuration mode. For multi-tenancy, create a VRF instance for each tenant.

   ip vrf tenant-vrf-name
   exit

2. Configure the anycast gateway MAC address all VTEPs use in all VXLAN virtual networks in Configuration mode.

   When a VM sends an Address Resolution Protocol (ARP) request for the anycast gateway IP address in a VXLAN virtual network, the nearest VTEP responds with the configured anycast MAC address. Configure the same MAC address on all VTEPs so that the anycast gateway MAC address remains the same if a VM migrates to a different VTEP. Because the configured MAC address is automatically used for all VXLAN virtual networks, configure it in global Configuration mode.

   ip virtual-router mac-address mac-address

3. Configure a virtual-network interface, assign it to the tenant VRF, and configure an IP address.

   The interface IP address must be unique on each VTEP, including VTEPs in VLT pairs. You can configure an IPv6 address on the virtual-network interface. Different virtual-network interfaces you configure on the same VTEP must have virtual-network IP addresses in different subnets. If you do not assign the virtual-network interface to a tenant VRF, it is assigned to the default VRF.

   interface virtual-network vn-id
   ip vrf forwarding tenant-vrf-name
   ip address ip-address/mask
   no shutdown
   exit

4. Configure an anycast gateway IPv4 or IPv6 address for each virtual network in INTERFACE-VIRTUAL-NETWORK mode. This anycast IP address must be in the same subnet as the IP address of the virtual-network interface in Step 3.

   Configure the same IPv4 or IPv6 address as the anycast IP address on all VTEPs in a virtual network. All hosts use the anycast gateway IP address as the default gateway IP address in the subnet that connects to the virtual-network interface configured in Step 3. Configure the anycast gateway IP address on all downstream VMs. Using the same anycast gateway IP address allows host VMs to move from one VTEP to another VTEP in a VXLAN. Dell EMC recommends using an anycast gateway in both VLT and non-VLT VXLAN configurations.

   interface virtual-network vn-id
   ip virtual-router address ip-address

The following tables show how to use anycast gateway IP and MAC addresses in a data center with three virtual networks and multiple VTEPs:

• Globally configure an anycast MAC address for all VTEPs in all virtual networks. For example, if you use three VTEP switches in three virtual networks:

  Table 1. MAC address for all VTEPsMAC address for all VTEPs

  Virtual network	VTEP	Anycast gateway MAC address
  VNID 11	VTEP 1 VTEP 2 VTEP 3	00.11.22.33.44.55 00.11.22.33.44.55 00.11.22.33.44.55
  VNID 12	VTEP 1 VTEP 2 VTEP 3	00.11.22.33.44.55 00.11.22.33.44.55 00.11.22.33.44.55
  VNID 13	VTEP 1 VTEP 2 VTEP 3	00.11.22.33.44.55 00.11.22.33.44.55 00.11.22.33.44.55

• Configure a unique IP address on the virtual-network interface on each VTEP across all virtual networks. Configure the same anycast gateway IP address on all VTEPs in a virtual-network subnet. For example:

  Table 2. IP address on the virtual-network interface on each VTEPIP address on the virtual-network interface on each VTEP

  Virtual network	VTEP	Virtual-network IP address	Anycast gateway IP address
  VNID 11	VTEP 1 VTEP 2 VTEP 3	10.10.1.201 10.10.1.202 10.10.1.203	10.10.1.254 10.10.1.254 10.10.1.254
  VNID 12	VTEP 1 VTEP 2 VTEP 3	10.20.1.201 10.20.1.202 10.20.1.203	10.20.1.254 10.20.1.254 10.20.1.254
  VNID 13	VTEP 1 VTEP 2 VTEP 3	10.30.1.201 10.30.1.202 10.30.1.203	10.30.1.254 10.30.1.254 10.30.1.254