The NAS IP Address Attribute is set to the loopback address (when configured) by default instead of the RADIUS server source-address if it is different from the loopback address.

This article explains what must be done to set the NAS IP Address Attribute to use the RADIUS server source address.

Example

[edit system]

radius-server {
    192.0.2.1 {
        port 1645;
        accounting-port 1646;
        timeout 5;
        retry 1;
        source-address 192.0.2.129;
    }
    192.0.2.2 {
        port 1645;
        accounting-port 1646;
        timeout 5;
        retry 1;
        source-address 192.0.2.129;
    }
} 

While dumping the contents of the connection that is leaving the fxp0 port, notice that the NAS IP Address Attribute is set to 192.0.2.255 and not 192.0.2.129 as desired.

root@router> monitor traffic interface fxp0 detail matching "host 192.0.2.1"
Address resolution is ON. Use <no-resolve> to avoid any reverse lookup delay.
Address resolution timeout is 4s.
Listening on fxp0, capture size 1514 bytes

12:23:56.559705 Out IP (tos 0x0, ttl  64, id 37373, offset 0, flags [none], proto: UDP (17), length: 116) 192.0.2.129.57464 >  192.0.2.1.1645: RADIUS, length: 88
        Access Request (1), id: 0x3c, Authenticator: 561182af66c1111346f8a174e
          Username Attribute (1), length: 11, Value: test_user
          Password Attribute (2), length: 18, Value:
          NAS ID Attribute (32), length: 17, Value: router
          Calling Station Attribute (31), length: 16, Value: 192.0.2.129
          NAS IP Address Attribute (4), length: 6, Value: 192.0.2.255 

This is because the NAS IP Address Attribute is set to use the loopback address (when configured) by default.

To set the ​NAS IP Address Attribute to use the RADIUS server source-address, the attribute must be explicitly configured, as follows:

set system radius-options attributes nas-ip-address <ip-address>