RADIUS not using Loopback IP as Source IP even when configured

Hi,

I am seeing an issue where Juniper EX4300 is not using the Source-IP of a loopback in the RADIUS packets it sends out. Interestingly - in the NAS-IP attribute it still sends the Loopback IP I configiured. Basically the Source-IP of the RADIUS UDP packet and NAS IP are different. Its using the IP address of my uplink which has reachability towards the RADIUS server in the IP Header and puts the RADIUS attribute NAS-IP with the loopback IP. This is causing some problems for me and I would like both the IP header and NAS-IP to use the loopback. Any knobs I need to be aware of achieve this ?

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Thanks in Advance.