Dell PowerEdge M420 Reference Manual page 795

Default Configuration
If a RADIUS server has been configured on the switch, the default attribute 4
value is the RADIUS server IP address.
Command Mode
Global Configuration mode
User Guidelines
This command has no user guidelines.
Example
The following example sets the NAS IP address in RADIUS attribute 4 to
192.168.10.22.
console(config)#radius-server attribute 4
192.168.10.22
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802.1x Commands