When using a Nexus node in VIRL, you may be unable to enable features due to licensing. For example:

switch(config)# feature ospf
Feature grace period is disabled

Grace licensing can be enabled, which allows features to be used for up to 120 days. Note, this applies to physical equipment too, not just VIRL nodes:

switch(config)# license grace-period

Features can now be enabled:

switch(config)# feature ospf
LAN_ENTERPRISE_SERVICES_PKG license not installed. ospf feature will be shutdown
 after grace period of approximately 120 day(s) 
switch(config)# 2016 Aug 25 04:19:07 switch %LICMGR-2-LOG_LIC_NO_LIC: No license(s) present for feature LAN_ENTERPRISE_SERVICES_PKG. Application(s) shut down in 119 days.
2016 Aug 25 04:19:07 switch %LICMGR-2-LOG_LICAPP_NO_LIC: Application ospf running without LAN_ENTERPRISE_SERVICES_PKG license, shutdown in 119 days