Understanding the Infiniband Subnet

Intel has published a easy-to-understand article on Infiniband Subnetting. "Understanding the InfiniBand Subnet Manager"

From the article:

The InfiniBand subnet manager (OpenSM) assigns Local IDentifiers (LIDs) to each port connected to the InfiniBand fabric, and develops a routing table based off of the assigned LIDs. 
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A typical InfiniBand installation using the OFED package will run the OpenSM subnet manager at system start up after the OpenIB drivers are loaded. This automatic OpenSM is resident in memory, and sweeps the InfiniBand fabric approximately every 5 seconds for new InfiniBand adapters to add to the subnet routing tables. This usage will be sufficient for most installations, and can be controlled using the following commands:

/etc/init.d/opensmd start
/etc/init.d/opensmd stop
/etc/init.d/opensmd restart
/etc/init.d/opensmd status

For more information, read the article.