VXLAN EVPN Leaf and Spine – Part 4 – Anycast Gateways

In this part we are going to look at the anycast gateway setup of the topology. This will help get the servers off their local network.

Lets remind ourselves of the topology:

Anycast gateways will be configured on each of the leaves using a virtual mac address so that mobility can be achieved without having to re-arp for the gateway MAC address. The same IP and MAC will be configured on each leaf.

Anycast basically means that everything has the same IP address and the closest instance of that IP address will be used when its requested. This is how services like Cloudflare work so you are routed to the closest node into their network.

Virtual Anycast MAC address

This anycast mac address should be configured on each leaf:

fabric forwarding anycast-gateway-mac aaaa.bbbb.cccc

We will see this Mac address in the ARP table of the clients as the Gateway.

SVI Configuration

Now, we can configure the SVI interfaces with the anycast IP addresses. In this topology we have vlan 10 and 20. This configuration is for all leaves:

interface Vlan10
  no shutdown
  ip address 10.10.1.254/24
  fabric forwarding mode anycast-gateway

interface Vlan20
  no shutdown
  ip address 10.20.1.254/24
  fabric forwarding mode anycast-gateway

Verification

Now, we can verify the configuration by trying to ping the local anycast gateway from a server:

server-0-vl10:~$ ping 10.10.1.254
PING 10.10.1.254 (10.10.1.254): 56 data bytes
64 bytes from 10.10.1.254: seq=0 ttl=42 time=2.969 ms
64 bytes from 10.10.1.254: seq=1 ttl=42 time=1.933 ms
64 bytes from 10.10.1.254: seq=2 ttl=42 time=1.721 ms
64 bytes from 10.10.1.254: seq=3 ttl=42 time=1.799 ms
64 bytes from 10.10.1.254: seq=4 ttl=42 time=1.841 ms
^C
--- 10.10.1.254 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 1.721/2.052/2.969 ms

server-0-vl10:~$ arp -a
? (10.10.1.254) at aa:aa:bb:bb:cc:cc [ether]  on eth0

We can see the pings are successful and also we can see the virtual mac address of the gateway too from the local arp table.

In the next part, we will move onto the L3VNI section. Just having anycast gateways doesn't give us layer 3 connectivity between vlan 10 and vlan 20, we need some other things layered on top.