File:Highly available HMC and network architecture.jpg

Source: redp-4637-00 IBM Power720 and 740 Technical Overview and Introduction. Figure 2.26.

If redundant HMC function is desired, the servers can be attached to two separate HMCs to address availability requirements. Both HMCs must have the same level of Hardware Management Console Licensed Machine Code Version 7 (#0962) to manage POWER7 processor-based servers or an environment with a mixture of POWER5, POWER5+, POWER6, POWER6+ and POWER7 processor-based servers. The HMCs provide a locking mechanism so that only one HMC at a time has write access to the service processor. Depending on your environment, you have multiple options to configure the network. Only the hardware management networks (LAN1 and LAN2) are shown as highly available in this diagram for simplicity. However, the management network (LAN3) can be made highly available by using a similar concept and adding more Ethernet adapters to LPARs and HMCs. Both HMCs must be on a separate VLAN, to protect from a network failure. Each HMC can be a DHCP server for its VLAN. In a configuration with multiple systems or HMCs, the customer is required to provide switches or hubs to connect each HMC to the server FSP Ethernet ports in each system. One HMC must connect to the port labeled as HMC Port 1, and a second HMC must be attached to HMC Port 2. This provides redundant connections for the HMCs and the service processor.