Chapter 8. Hardware Management Console overview 201 The third interface is an optional additional Ethernet connection that can beused for remote management of the HMC. This third interface can also beused to provide a separate HMC connection to different groups of logicalpartitions. For example, you could do any of the following:– An administrative LAN that is separate from the LAN on which all the usualbusiness transactions are running. Remote administrators could accessHMCs and other managed units using this method.– Different network security domains for your partitions, perhaps behind afirewall with different HMC network connections into each of those twodomains.8.3.1 Private and open networks in the HMC environmentThe connection between the HMC and the p5-590 and the p5-595 must be aprivate network in a one-HMC configuration.In a private network, the only elements on the physical network are the HMC andthe service processors of the managed systems. In addition, the HMC providesDynamic Host Configuration Protocol (DHCP) services on that network that allowit to automatically discover and assign IP configuration parameters to thoseservice processors. You can configure the HMC to select one of several differentaddress ranges to use for this DHCP service, so that the addresses provided tothe service processors do not conflict with addresses used on the other networksto which the HMC is connected. The DHCP services allow the elements on theprivate service network to be automatically configured and detected by the HMC,while at the same time preventing address conflicts on the network.On a private network all of the elements are controlled and managed by theHMC. The HMC also acts as a functional firewall, isolating that private networkfrom any of the open networks to which the HMC is also attached. The HMCdoes not allow any IP forwarding; clients on one network interface of the HMCcannot directly access elements on any other network interface.It is required that you implement network communications through a privatenetwork.Note: With the rack-mounted HMC, if an additional (third) Ethernet port isinstalled in the HMC (by using a PCI Ethernet card), then that PCI-cardbecomes the eth0 port. Normally (without the additional card), eth0 is the firstof the two integrated Ethernet ports.
