Connectivity Guide

Enable overlay routing between virtual networks
The previous sections described how a VTEP switches trac between hosts within the same L2 tenant segment, the virtual network, and
transports trac over an IP underlay fabric. This section describes how a VTEP enables hosts in dierent L2 segments belonging to the
same tenant VRF communicate with each other.
NOTE: On the S4248-ON switch, IPv6 overlay routing between virtual networks is not supported with static VXLAN. IPv6
overlay routing is, however, supported with BGP EVPN.
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 trac 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 trac routing between virtual networks, congure 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 ecient trac forwarding on a VTEP, OS10 supports distributed 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 dierent VTEPs, congure a common virtual IP address, 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, congure a dierent 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 Conguration mode. For multi-tenancy, create a VRF instance for each
tenant.
ip vrf tenant-vrf-name
exit
2 Congure the anycast gateway MAC address all VTEPs use in all VXLAN virtual networks in Conguration 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 congured anycast MAC address. Congure the same MAC address on all VTEPs so that the
anycast gateway MAC address remains the same if a VM migrates to a dierent VTEP. Because the congured MAC address is
automatically used for all VXLAN virtual networks, congure it in global Conguration mode.
ip virtual-router mac-address mac-address
3 Congure a virtual-network interface, assign it to the tenant VRF, and congure an IP address.
The interface IP address must be unique on each VTEP, including VTEPs in VLT pairs. You can congure an IPv6 address on the
virtual-network interface. Dierent virtual-network interfaces you congure on the same VTEP must have virtual-network IP
addresses in dierent 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 Congure 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.
Congure 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 congured in Step
3. Congure 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 congurations.
interface virtual-network vn-id
ip virtual-router address ip-address
684
VXLAN