When we bind the radius policy globally with accounting set as ON, NS will automatically send the accounting request for nsroot account to radius server, even the nsroot account external auth is disabled.

Configuration:
add authentication radiusAction radius -serverIP 10.158.151.242 -serverPort 1812 -radKey 05090aa2b1f876b9b6ce7e2429a6000e19e902eaedc146cea1a8a2a5176317ad -encrypted -encryptmethod ENCMTHD_3 -accounting ON
add authentication radiusPolicy radius ns_true radius
bind system global radius -priority 100
set system user nsroot 11baf32178ccb0df2c0e9f576b81c6dc2d40f62aca951daae -encrypted -externalAuth DISABLED -timeout 86400
set system user lily 1aca7c9cbeaf8cbbd3fb04b35e7bed973adbc1c26f9a01dd4 -encrypted -externalAuth DISABLED -timeout 900 -logging ENABLED

From aaad.debug, the following message ONLY pops up for nsroot user:
root@NS105HA1# cat /tmp/aaad.debug
Thu Aug 10 11:13:05 2017
/usr/home/build/rs_110_70_8_RTM/usr.src/netscaler/aaad/naaad.c[1298]: process_kernel_socket handling accounting message for user :nsroot, vsid :1081
Thu Aug 10 11:13:05 2017
/usr/home/build/rs_110_70_8_RTM/usr.src/netscaler/aaad/naaad.c[3334]: register_timer setting timer 15062

Set accouting off to avoid log flooding:
set authentication radiusAction radius -accounting off
 

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Problem Cause

It's the expected behaviour:
The authentication and accounting are different operations:
>>>> ExternalAuth disable means you are not delegating authentication operation to external server.
>>>> Accounting ON means for all user operation, you are sending accounting information to particular external server.

Testing Result:
Have checked the accounting behavior on 10.5 62.9 build and 11.1 54.14 build and following are the observations  :
(It consists for all builds and all users.) For both  11.1 54.14  and 10.5 62.9 build, accounting messages are seen for (when accounting is on in radiusaction):
 
•             “nsroot” with external auth disabled
•             “nsroot” with  external auth enabled
•             local system user with external auth disabled
•             local system user with external auth as enabled
 
Test details :
On 10.5 62.9 build:
# Apply Radius config with accounting ON.
i. # login as nsroot , accounting msgs are seen :
 
Tue Aug 29 16:37:28 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1149]: process_kernel_socket nsaad: AAA_TACACS_ACCOUNT**
 
Tue Aug 29 16:37:28 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1174]: process_kernel_socket handling accounting message for user :nsroot, vsid :972 Tue Aug 29 16:37:28 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2925]: register_timer setting timer 85 Tue Aug 29 16:37:28 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[1896]: process_radius Got RADIUS event Tue Aug 29 16:37:28 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2994]: unregister_timer releasing timer 85 Tue Aug 29 16:37:28 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[2014]: process_radius received accounting response
 
ii. Login as nsroot with external auth as disabled. Accounting msgs are seen :
               
Tue Aug 29 16:38:34 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1149]: process_kernel_socket nsaad: AAA_TACACS_ACCOUNT**
 
Tue Aug 29 16:38:34 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1174]: process_kernel_socket handling accounting message for user :nsroot, vsid :972 Tue Aug 29 16:38:34 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2925]: register_timer setting timer 87 Tue Aug 29 16:38:34 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[1896]: process_radius Got RADIUS event Tue Aug 29 16:38:34 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2994]: unregister_timer releasing timer 87 Tue Aug 29 16:38:34 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[2014]: process_radius received accounting response
 
iii. Login as local system user, Accounting msgs are seen :
               
Tue Aug 29 16:39:20 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1149]: process_kernel_socket nsaad: AAA_TACACS_ACCOUNT**
 
Tue Aug 29 16:39:20 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1174]: process_kernel_socket handling accounting message for user :test, vsid :972 Tue Aug 29 16:39:20 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2925]: register_timer setting timer 90 Tue Aug 29 16:39:20 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[1896]: process_radius Got RADIUS event Tue Aug 29 16:39:20 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2994]: unregister_timer releasing timer 90 Tue Aug 29 16:39:20 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[2014]: process_radius received accounting response Tue Aug 29 16:39:21 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[500]: main timer 1 firing...
 
iv.  Login as local system user, external auth as disabled. Accounting msgs are seen :
 
Tue Aug 29 16:40:16 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1149]: process_kernel_socket nsaad: AAA_TACACS_ACCOUNT**
 
Tue Aug 29 16:40:16 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[1174]: process_kernel_socket handling accounting message for user :test, vsid :972 Tue Aug 29 16:40:16 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2925]: register_timer setting timer 93 Tue Aug 29 16:40:16 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[1896]: process_radius Got RADIUS event Tue Aug 29 16:40:16 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/naaad.c[2994]: unregister_timer releasing timer 93 Tue Aug 29 16:40:16 2017
/usr/home/build/rs_105_62_6_RTM/usr.src/netscaler/aaad/radius_drv.c[2014]: process_radius received accounting response
 
On 11.1 54.14 build :
 
 
# Apply Radius config
i.              login as nsroot , external auth is enabled accounting msgs are seen:
 
root@ns# cat /tmp/aaad.debug
Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[774]: process_kernel_socket partition id is 0 Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1281]: process_kernel_socket nsaad: AAA ACCOUNTING**
 
Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1313]: process_kernel_socket handling accounting message for user :nsroot, vsid :758 Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3465]: register_timer setting timer 37 Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2048]: process_radius Got RADIUS event Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3534]: unregister_timer releasing timer 37 Tue Aug 29 11:13:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2177]: process_radius received accounting response
 
 
ii.             Login as nsroot, external auth is disabled . Accounting msgs are seen:
 
Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[774]: process_kernel_socket partition id is 0 Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1281]: process_kernel_socket nsaad: AAA ACCOUNTING**
 
Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1313]: process_kernel_socket handling accounting message for user :nsroot, vsid :758 Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3465]: register_timer setting timer 39 Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2048]: process_radius Got RADIUS event Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3534]: unregister_timer releasing timer 39 Tue Aug 29 11:14:36 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2177]: process_radius received accounting response
 
 
iii.            Login as local user , external auth enabled. Accounting msgs are seen:
Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[774]: process_kernel_socket partition id is 0 Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1281]: process_kernel_socket nsaad: AAA ACCOUNTING**
 
Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1313]: process_kernel_socket handling accounting message for user :qa, vsid :758 Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3465]: register_timer setting timer 41 Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[774]: process_kernel_socket partition id is 0 Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[998]: process_kernel_socket call to authorize user :qa, remote address:10.252.241.164, command:shell, vsid:758 Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2048]: process_radius Got RADIUS event Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3534]: unregister_timer releasing timer 41 Tue Aug 29 11:15:18 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2177]: process_radius received accounting response
 
 
 
iv.           Login as local user , external auth is disabled for this user . accounting msgs are seen:
 
Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[774]: process_kernel_socket partition id is 0 Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1281]: process_kernel_socket nsaad: AAA ACCOUNTING**
 
Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[1313]: process_kernel_socket handling accounting message for user :qa, vsid :758 Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3465]: register_timer setting timer 44 Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[774]: process_kernel_socket partition id is 0 Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[998]: process_kernel_socket call to authorize user :qa, remote address:10.252.241.164, command:shell, vsid:758 Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2048]: process_radius Got RADIUS event Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/naaad.c[3534]: unregister_timer releasing timer 44 Tue Aug 29 11:16:15 2017
/home/build/rs_111_54_8_RTM/usr.src/netscaler/aaad/radius_drv.c[2177]: process_radius received accounting response