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Network Connections of a HMC
The main task of an HMC is to manage IBM Power systems (managed systems). In order to be able to fulfill this task, an HMC requires network connections to the managed systems to be managed. The managed systems have two special HMC ports for this purpose (HMC 1 and HMC 2). This allows connection to one HMC or two HMCs (redundancy). The HMC ports belong to the FSPs (Flexible Service Processor) or more recently eBMCs (enterprise Baseboard Management Controller) of the managed systems.
In a typical configuration, the managed systems are connected to an HMC via their own network. This is then often referred to as a private network or service network. In order to simplify the IP configuration of the managed systems (more precisely the FSPs or eBMCs), the HMC is configured as a DHCP server in such a service network.
If there is only one HMC, only the first HMC port (HMC 1) is used. If the HMC is not available, the managed systems and LPARs continue to run unaffected, but administration can no longer be carried out.
For redundancy reasons, two HMCs are usually used. If one of the two HMCs fails (or is rebooted), administration can still be carried out via the second HMC.
The first HMC port (HMC 1) of the managed systems is connected to the service network of the first HMC (HMC1) (in the picture “private net HMC1” in red). The second HMC port (HMC 2) of the managed systems is connected to the service network of the second HMC (HMC2) (in the picture “private net HMC2” in blue).
Note: If the HMCs act as DHCP servers, no HMC may be connected to both service networks!
Access by administrators is usually via another network, often referred to as a public network or open network. Typically both HMCs are connected via the same public network.
There are other configuration options, but they will not be discussed here.
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