Merge pull request #48092 from kquinn1204/BZ-2109453

BZ-2109453 adding note on client and subnet

Author: bergerhoffer

modules/nw-metallb-layer2.adoc

@@ -7,8 +7,12 @@
 [id="nw-metallb-layer2_{context}"]
 = MetalLB concepts for layer 2 mode
 
-In layer 2 mode, the `speaker` pod on one node announces the external IP address for a service to the host network.
-From a network perspective, the node appears to have multiple IP addresses assigned to a network interface.
+In layer 2 mode, the `speaker` pod on one node announces the external IP address for a service to the host network. 
+From a network perspective, the node appears to have multiple IP addresses assigned to a network interface. 
+[NOTE]
+====
+Since layer 2 mode relies on ARP and NDP, the client must be on the same subnet of the nodes announcing the service in order for MetalLB to work. Additionally, the IP address assigned to the service must be on the same subnet of the network used by the client to reach the service. 
+====
 
 The `speaker` pod responds to ARP requests for IPv4 services and NDP requests for IPv6.