You don't have to reboot or anything. The setting is in effect right away for every NEW connection.
I pulled this information from an older discussion. I'd like to change the keepidle setting on my cluster but want to know what impact is required to change/set the value? Are node reboots required or services restart processes?  Thanks.  The current setting can be reviewed with the following command  isi_for_array -s 'sysctl net.inet.tcp.keepidle'  To set the value --  isi_sysctl_cluster net.inet.tcp.keepidle=300000  (5 minutes, value in milliseconds)  The next sysctl that would be of interest is the ping interval with is currently set at 75000 (75 Seconds).  The cluster will send 8 pings at a 75 second interval resulting in a 5 minute window for the client to respond.   To view the setting -- isi_for_array -s 'sysctl net.inet.tcp.keepintvl'
isilon keepidle setting change