Question:

We recently updated several AIX systems to AIX 7.3 TL4 SP0, and we observed a new RSCT daemon was now running on all the updated systems. The daemon is named mcproxy (/opt/rsct/bin/rmcproxyd).

What is the purpose of this new daemon?

# oslevel -s

7300-04-00-2546

# errpt | grep proxy

1D0FB551   0215180526 I O mcproxy        The daemon is started.

# lssrc -ls mcproxy

Subsystem         Group            PID          Status

 mcproxy          rsct             20709766     active

 HMC Status Information:

 +-----+---------------+------------+------------+--------------+

 | SLOT| HMC NAME      |   STATUS   | ACTIVE REQ | PENDING RESP |

 +-----+---------------+------------+------------+--------------+

 |     |               |            |            |              |

 +-----+---------------+------------+------------+--------------+

 |TOTAL|       0       |  H: 0 A: 0 |           0|             0|

 +-----+---------------+------------+------------+--------------+

 **(H => Handshake State, A => Active State)

# lssrc -s mcproxy

Subsystem         Group            PID          Status

 mcproxy          rsct             20709766     active

# ps -fp 20709766

     UID      PID     PPID   C    STIME    TTY  TIME CMD

    root 20709766  4653534   0 18:05:17      -  0:00 /opt/rsct/bin/rmcproxyd

Answer:

Support was added for “inband” HMC to OS communication (RMC Connection). This eliminates external network dependencies for RMC for OS versions that are enabled for in-band RMC.

The mcproxy subsystem has been introduced to handle "in-band" RMC communication from  AIX partitions to HMC via the hypervisor. This replaces existing network-based RMC connection  between the partition and the HMC. On supported systems "in-band" RMC communication is enabled by default. Unsupported systems automatically fallback to Network based RMC communication until upgraded or migrated to supported systems.

Requirements:

·      AIX 7.3 TL4/RSCT 3.3.4.0 or later

·      POWER 11 System and newer

·      POWER Hypervisor & Firmware 1110.10 or later

·      Partition running in P11 compatibility mode and higher

·      HMC version HMC V11 R1 M1111 or later

This new feature introduces secure and reliable RMC communication from the HMC to AIX partitions via the hypervisor. This replaces existing network-based RMC connection between the partition and the HMC. This is applicable only when a partition is running AIX version 7.3 Technology Level (TL) 4 and is using a processor compatibility mode of POWER11.

Please refer to:

https://delivery04-mul.dhe.ibm.com/sar/CMA/HMA/0dlqo/4/MF71745.readme.html

https://www.ibm.com/support/pages/power11-system-firmware-fix-history-release-levels-my11xx

https://www.ibm.com/docs/en/power11/9080-HEU?topic=partitions-secure-rmc-communication-through-hypervisor

Note: When RMC communication is via the hypervisor, the IP address shown for the partition on the HMC will be blank.

Note: At time of release (Dec 2025) when a partition is migrated back and forth multiple times between two Power11 systems, the partition may lose its RMC connection. To restore the RMC connection, log in to the affected partition as the root user and run the following commands:

stopsrc -s mcproxy; /opt/rsct/bin/rmcrefreshMD -s ctrmc; sleep 10; startsrc -s mcproxy

UPDATE: When I initially wrote this post Linux wasn't supported yet. As of HMC V11.2.1120.0, both RHEL 9.8 and RHEL 10.2 are now officially supported using the same in-band RMC communication. Refer to the official documentation: https://www.ibm.com/docs/en/power11/9080-HEU?topic=SSVEKM0/p11jau/p11jau_inbandRMCcommunication.html