ISG ip interface session

ip subscriber interface : It seems, only nas-port can be used as identifier

interface GigabitEthernet0/0/1
ip vrf forwarding INTERNET
ip address 30.30.30.1 255.255.255.0
negotiation auto
service-policy type control TAL_IP_POLICY_RULE
ip subscriber interface
end

class type control always event session-start
1 authorize aaa list pppoe password cisco identifier nas-port
2 set-timer IP_UNAUTH_TIMER 5
!

*Jul 24 07:18:02.240: RADIUS: User-Name [1] 34 “nas-port:192.168.1.230:0/0/1/1”
*Jul 24 07:18:02.240: RADIUS: User-Password [2] 18 *
*Jul 24 07:18:02.240: RADIUS: Vendor, Cisco [26] 19
*Jul 24 07:18:02.240: RADIUS: ssg-account-info [250] 13 “S30.30.30.1”
*Jul 24 07:18:02.240: RADIUS: NAS-Port-Type [61] 6 Virtual [5]
*Jul 24 07:18:02.240: RADIUS: NAS-Port [5] 6 0
*Jul 24 07:18:02.240: RADIUS: NAS-Port-Id [87] 9 “0/0/1/1”
*Jul 24 07:18:02.240: RADIUS: Service-Type [6] 6 Outbound [5]
*Jul 24 07:18:02.240: RADIUS: NAS-IP-Address [4] 6 192.168.1.230

Also I have opened a thread in cisco support community for this.

https://supportforums.cisco.com/thread/2230332