Edit: Some links no longer work. The SDMC never did take over from the HMC.
Originally posted June 21, 2011 on AIXchange
What do the best practices documents tell us about HMC private networks when communicating between HMC and flexible service processor (FSPs)? Is a private network switch or VLAN really needed between the HMC and the FSP? Can an HMC in a remote data center be used to manage machines over regular network links?
This 2007 document, authored by IBMers Ron Barker, Minh Nguyen, and Shamsundar Ashok, states:
“The network connection between the HMC and the FSP can be either private or open on low-end to mid-range servers. Private is preferred, and therefore a best practice. A private network is required for systems that have a BPA, such as the models 590, 595 and 575.
“In an open configuration, the FSP’s IP addresses must be set manually on each managed server. They cannot be DHCP clients of any server other than a managing HMC.
“Addresses can be set using the Advanced System Management Interface (ASMI) on the FSP. This involves directly connecting a laptop to one of the ports on the FSP and using HTTPS to log into one of the two pre-defined IP addresses. The HMC1 port defaults to 192.168.2.147; HMC2 defaults to 192.168.3.147. The systems administrator can login as user ‘admin’ using the default password ‘admin,’ which should be changed during the initial installation for security reasons. If no laptop is available, an ASCII terminal can be used on the native serial port to access the FSP menus in character mode.
“Remember, with POWER7, the addresses have changed to:
Service processor A HMC1 169.254.2.147, HMC2 169.254.3.147 and
Service processor B (if installed) HMC1 169.254.2.146 HMC2 169.254.3.146
“Open networks are used for communications between a logical partition and the HMC. This connection is largely to facilitate traffic over the Resource Monitoring and Control (RMC) subsystem, which is the backbone of Service Focal Point (SFP) and required for dynamic resource allocation. The open network also is the means by which remote workstations may access the HMC, and it could be the path by which an HMC communicates with IBM Service through an Internet connection.”
Though HMCs will be going away in favor of SDMC, the transition will be gradual. For the time being we need to keep our HMC skills sharp, and this is one question that frequently arises when customers plan to add new systems to an environment.
Recently I helped a client set up HMC communications over an open network in just this manner. We found that our FSP ports were still going 100MB, as the ports were requested to be set to 1000/Full Duplex. They wouldn’t link up to the network at that speed.
Once we had the HMC on the open network, we pointed the HMC to the new IP addresses we’d configured on the FSPs on the local machines. That worked. We then added managed systems that were located in a remote data center without a problem. Finally, we did the same thing with an HMC from the remote data center to manage the machines in the local data center.
While I wouldn’t recommend using a remote HMC for day-to-day tasks if a local one is available to you, this is a viable option when setting up machines.
How is the HMC set up in your environment? Please share your experiences in Comments.