Deployment Guide

Overlay ECMP for L3 prefix routes
If a tenant IP subnet extends between more than one VTEP, all VTEPs which host the subnet advertise its reachability using
Type-5 prefix routes.
● A VTEP that is locally connected to the tenant subnet uses local routes instead of remote routes.
● A VTEP that is not locally connected to the tenant subnet installs the remote routes using an ECMP group of overlay
next-hops.
The S4100-ON series, S5200-ON series, S4048T-ON, and S6010-ON switches that support native VxLAN routing — routing in
and out of tunnels (RIOT) — also support ECMP to process remote next-hop routes in the overlay network.
By default, overlay ECMP processing is disabled. After you enable overlay ECMP, reload the switch for the configuration change
to take effect.
Enable ECMP for overlay routing
● Enable an overlay ECMP profile or disable the configured profile in Configuration mode. Save the configuration and reload
the switch.
OS10(config)# hardware overlay-ecmp-profile mode {disable-overlay-ecmp | balanced-
overlay-ecmp}
OS10(config)# exit
OS10# write memory
OS10# reload
Display overlay ECMP profiles
● View the currently configured overlay ECMP routing profile and available resources:
show hardware overlay-ecmp-profile mode
Setting Mode Overlay ECMP Underlay ECMP
Group Path Group Path
Current default-overlay-ecmp 0 0 512 64
Next-boot balanced-overlay-ecmp 0 0 512 64
DHCP relay on VTEPs
Dynamic Host Configuration Protocol (DHCP) clients on hosts in the overlay communicate with a DHCP server using a DHCP
relay on the VTEP switch. To work seamlessly, VTEP DHCP relay transmits the virtual-network IP address of the relay interface
to the DHCP server.
By default, DHCP uses the giaddr packet field to carry these addresses to the server. In a VxLAN, which has overlay and
underlay subnets in the same default VRF, DHCP relay on VTEPs operates without user intervention. However, in a VXLAN in
which the underlay and overlay are in different VRFs, the default DHCP method is not successful. The IP tenant subnet is in the
overlay address space. The IP address where the VTEP is reachable is in the underlay address space. To transmit the IP subnet
of the client separately from the IP address where the VTEP is reachable, you must configure an additional DHCP sub-option (5
or 151) in DHCP relay agent option 82.
Because OS10 does not support the required sub-options in DHCP relay agent option 82, the giaddr packet field must
contain the virtual-network IP address of the relay interface, and this IP address must be reachable from the DHCP server in
the underlay. Each VTEP that acts as a DHCP relay must have its virtual-network IP address installed using a route leaking
mechanism as a route to the underlay and advertised to all underlay routers, including the spine switches.
Similarly, the DHCP server in the underlay VRF must be reachable from the client tenant VRF in the overlay. Configure a static
route for the DHCP server subnet in the underlay default VRF, and leak the static route to the client tenant VRF in the overlay.
This configuration sets up a bi-directional communication between the client and DHCP server across the virtual networks. The
route-leaking configuration is not required if the VxLAN overlay subnet and underlay subnet are in same default VRF.
Configure DHCP relay on VTEPs
1. Configure the IP address of the virtual-network relay interface in the non-default tenant VRF as a static route in the default
VRF.
OS10(config)# ip route 10.10.0.2/32 interface virtual-network 10
16
VXLAN