InfiniBand is an interconnect technology that breaks through the bandwidth and fanout limitations of PCI bus by switching from traditional shared bus architecture to a switched fabric architecture. It is a switched fabric I/O technology that ties together servers, storage devices, and network devices. Instead of sending data in parallel, which is what PCI does, InfiniBand sends data in serial and can carry multiple channels of data at the same time in a multiplexing signal.

IBM® AIX® 610 supports InfiniBand hardware and various protocols that run over InfiniBand. This article shows how to configure InfiniBand and set up IP over InfiniBand interface (IPoIB) in AIX. Also, this article explains how to use RDS (Reliable Datagram Sockets), a protocol (similar to UDP) designed to work over InfiniBand to send and receive data using sockets.


Puja Leekha (, Manager - Regression and Integrated FVT, AIX India, IBM

author photoPuja Leekha is a Senior Staff Software engineer for IBM India with over 7 years of experience in system and networking technologies and is currently the project manager with the regression and integrated FVT team. Prior to her current assignment, she led the Communication IO FVT Team for 2 years. You can contact her at

20 May 2008

Also available in Chinese

Configuring InfiniBand

Internet Protocol (IP) packets can be sent over an InfiniBand (IB) network interface by using IP over IB (IPoIB). IPoIB encapsulates the IP packets into IB packets and sends using the IB interface. In order to use IPoIB, you must install and configure the ICM driver and at least one IB device in the system. The following steps are required to configure an IB device and then configure IPoIB using the ICM.

  1. Before configuring InfiniBand, you need to check to see if the IB device, for instance InfiniBand HCA (InfiniBand Host Channel Adapter), is configured and is in “Available” state on your AIX box. To check the status, do the following:
    #  lsdev -Cc adapter | grep "host channel"
    iba0 Available  InfiniBand host channel adapter


    # lsdev -Cc adapter | grep "HCA"
    iba0  Available 01-00 PCIE Dual Port HCA (b3157862)
  2. Configure ICM (InfiniBand Communication Manager). To configure ICM, do the following:

    smit icm -> Add an InfiniBand Communication Manager -> Add an InfiniBand Communication Manager à select ICM (as the ‘Name of IB Communication manager to Add’) and you will see the screen as shown in Figure 1.

    Figure 1. Configure ICM

    Click Enter to use the default values for each of the fields. The next screen will show ‘Command: OK’ and   ‘icm Available’. ICM configuration is done.

    To check if ICM has been configured, do

    # lsdev -l icm
    icm Available  InfiniBand Communication Manager
  3. Configure InfiniBand Network interface. IB interface can be configured using command line interface or SMIT user interface.

    To configure IB interface using SMIT do:

    smit inet -> Change / Show Characteristics of a Network interface -> select ib0 ( IP over InfiniBand Network Interface). You will see the screen as shown in Figure 2.

    Figure2. Configure IB interface

    Enter the values for the following fields:

    • Internet Address ( for example,
    • Network mask (for example,
    • HCA adapter (the one we configured in step 1, iba0)
    • Adpater’s port number . There are two ports, Port 1 and Port 2. Use the command ibstat to check which port is Active. If both are active, select that you would like to use, as per your network configuration.
    • Current state – up

    Use the default values for the remaining fields.

    The next screen shows ‘Command: OK’ and ‘ib0 changed’. IB interface configuration is done.

    To check the IB interface status, run the ifconfig command.

    # ifconfig ib0
    inet netmask 0xffffff00 broadcast
    tcp_sendspace 131072 tcp_recvspace 131072 rfc1323 1

Configure the IB interface using the command line interface.

Step 1 and step 2 are the same as above. For step 3, do the following:

# /usr/sbin/mkiba  -a  -i ib0 -A iba0  -p 2  -P  0xFFFF  -S up 
 -m -M 2044 ib0 changed

The syntax for the mkiba command is:

 /usr/bin/mkiba {-a address -i interface -A ib_adapter -p ib_port [-P P_KEY]  
          [-m subnet_mask]
  [-S state] [ -M mtu ] [ -q queue_pair_size ] [ -Q Q_KEY ] [-k superpacket] }


-a address IP address of the interface specified by –I (must be in dotted decimal notation)
-i interfaceInterface to associate with the -a IP address
-A ib_adapterIB adapter associated to the interface
-p ib_portIB port associated with the IB adapter. (Defaults to 1)
-P p_key Partition key associated with the IB port. Key ( Please note that once configured partition key cannot be changed. The user must obtain the Partition key from the network administrator before configuring).
-m subnet_mask Subnetwork mask (dotted decimal or 0x notation)
-S state down,up,detach : The state of the ib interface.
-M ib_mtuHCA MTU required
-q srq_sizeSend and Receive queue sizes
-Q Q_KEYQ_Key associated with the multicast group
-k superpacketSuperpacket feature on or off

Keep the following in mind:

  • The –k option for superpacket is available from AIX 61B and 53N releases onwards; the lower releases do not contain the superpacket feature. Also, when this feature is enabled, it gives a good performance boost. It allows TCP/IP to send 64KB datagrams to the interface, which can increase performance. Note that this feature is supported only in AIX from an AIX host to AIX host, as long as interfaces at both the hosts are enabled with this feature.
  • The –M option for HCA MTU size. AIX supports 4K physical MTU if the switch and the adapter support it. The interface for the first time, expects the user to create the broadcast multicast group in the switch. If the group is not there, always a 2K multicast group will be created by default. So if you have a 4K physical MTU supported adapter and switch, and you don't create the broadcast group in the switch, the interface will lower the MTU to 2K by creating a multicast group of 2K.

Run ifconfig to check the IB interface status.

# ifconfig ib0
    inet netmask 0xffffff00 broadcast
     tcp_sendspace 131072 tcp_recvspace 131072 rfc1323 1

You are done! IB interface is configured.

To verify that all is working well, configure two nodes using the steps indicated above and run ping between the two notes. If ping works, IB is configured properly.

Configuring RDS

RDS uses the IB network interface for communication. Thus, IpoIB and IB network interface should be configured in order to use RDS protocol.

Before loading the RDS driver on the systems that you would like to communicate with using RDS, check if the IB network interfaces on those systems are able to ping each other.

Loading RDS

Run the following command to load RDS:

# bypassctrl load rds

If you receive the error Exec format error .., the IB interface is not configured. See Configuring InfiniBand and configure the IB interface and then try to load RDS using bypassctrl.

If RDS is already loaded, the error /usr/lib/drivers/rds already loaded displays.

To check that the RDS driver was loaded successfully, run the following:

# genkex | grep rds
         47e1000    53770 /usr/lib/drivers/rds

If a socket is created to use RDS protocol and returns the error socket: Addr family not supported by protocol, the RDS driver is not loaded and you need to load it. Also, note that on a reboot, the RDS driver gets unloaded and thus needs to be reloaded using the bypassctrl utility after every reboot.

rdsctrl utility

Once RDS is loaded, use the rdsctrl (/usr/sbin/rdsctrl) utility to get the RDS statistics for modifying the tuneable parameters and for diagnostics.

The # rdsctrl stats command displays various RDS statistics.

The statistics can be reset using

# rdsctrl stats reset .

Tuning parameters

The following RDS parameters can be tuned after RDS is loaded, but before any RDS application is run. To set any parameter, use the syntax:

# rdsctrl set <tunable parameter>=<value to be set>
  • The rds_sendspace parameter refers to the high-water mark of the per-flow send buffer. (There may be multiple flows per socket.)

    The default value is 524288 bytes (512KB). The value is set using the command:

      # rdsctrl set rds_sendspace=<value in bytes>
  • rds_recvspace refers to the per-flow high-water mark of the per-socket receive-buffer. For every additional flow to this socket, the receive high-water mark is bumped up by this value.

    The default value is 524288 bytes  (512 KB). The value is set using the command:

    # rdsctrl set rds_recvspace=<value in bytes>

    For good RDS streaming performance, the rds_sendspace and rds_recvspace parameters must be at least four times the largest RDS sendmsg size. RDS sends an ACK for each 4 messages received and if the rds_recvspace is not at least 4 times the message size, the throughput will be very low.

  • rds_mclustsize refers to the size of the individual memory cluster, which is also the message fragment size. The default size is 16384 bytes (16KB). The value, always a multiple of 4096, is set using the command: # rdsctrl set rds_mclustsize=<multiple of 4096, in bytes>

    The rds_mclustsize value must be the same on all machines (nodes) in the cluster. Changing this value also has performance implications.

The current values that are set for the tuneable parameters can be retrieved using the command:

   # rdsctrl get <tunable parameter>

If this is run without any tuneable parameter, it gives the entire list of tuneable parameters

# rdsctrl get provides the list of tuneable parameters with their current values.

      # rdsctrl get
	      rds_conn_block_limit = 100
	                 rds_acksz = 180
	                 rds_txqsz = 1024
	                 rds_rxqsz = 1024
	                        rds_mclustsize = 16384
	                          rds_recvspace = 524288
	                          rds_sendspace = 524288

Data-structure dumps

Various RDS structures can be dumped for troubleshooting purposes. The command to use is # rdsctrl dump <structure>

<structure> can be any one of the following:

  • IBC (the details of the IB Reliable Connection)
  • sendcb (the flow details)
  • pcb (the RDS socket PCB details)


Using the information in this article you learned how to configure InfiniBand over AIX and configure and use RDS over InfiniBand. You learned the commands used for configuring RDS; however, to understand RDS protocol, refer the Resources section for additional information.



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