You can connect to a specific portal on a discovered target by using the iscsiadm command.
For SLES:
iscsiadm --mode node --target <IQN> --portal x.x.x.x --login
Such as iscsiadm --mode node --target iqn.1986-03.com.ibm:2145.cluster10g1.node1 --portal 192.168.64.191 --login.
For RHEL:
iscsiadm --mode node --targetname --portal x.x.x.x --login
Such as iscsiadm --mode node --targetname iqn.1986-03.com.ibm:2145.cluster10g1.node1 --portal 192.168.64.191 --login.