Article ID: 317239 - View products that this article applies to.
This article was previously published under Q317239
If you are using a deployment that uses both Network Load Balancing and an F5 Networks BIG-IP load balancer, the Network Load Balancing hosts may be unable to communicate with other servers that are load-balanced by the BIG-IP load balancer. This compatibility problem may occur if the Network Load Balancing cluster runs in Network Load Balancing's unicast mode and connects to BIG-IP over the same subnet on which Network Load Balancing receives client traffic.
This problem may occur because the recent BIG-IP software release includes a new security check that discards Address Resolution Protocol (ARP) packets in which the packet's hardware media access control (MAC) address does not match the source MAC address in the data fields of the ARP packet. If you run Network Load Balancing in unicast mode, Network Load Balancing's default behavior modifies the hardware MAC address of all outgoing packets, including ARP packets. This behavior causes these packets to be discarded by BIG-IP.
Network Load Balancing's behavior is intended to make sure that incoming packets for a Network Load Balancing cluster are simultaneously received by all Network Load Balancing hosts on the same subnet. To do so, Network Load Balancing sets the MAC address of its network adapter on each cluster host to the same value that is associated with the virtual Internet Protocol (IP) addresses. Network Load Balancing also modifies all outgoing packets to mask this address and thereby prevents the address's discovery by the switch to which Network Load Balancing hosts are connected. As a result, the switch broadcasts the incoming packets that are intended for the Network Load Balancing cluster's MAC address on all ports, and all Network Load Balancing hosts simultaneously receive these packets.
To work around this compatibility problem, use any of the following methods: