RADIUS Attribute - NAS-IP-Address
As Per RFC2865
This Attribute indicates the identifying IP Address of the NAS which is requesting authentication of the user, and SHOULD be unique to the NAS within the scope of the RADIUS server. NAS-IP-Address is only used in Access-Request packets. Either NAS-IP-Address or NAS-Identifier MUST be present in an Access-Request packet.
The NAS-IP-Address MUST NOT be used to select the shared secret used to authenticate the request. The source IP address of the Access-Request packet MUST be used to select the shared secret.
A summary of the NAS-IP-Address Attribute format is shown below. The fields are transmitted from left to right.
Type (IETF Attribute Number) = 4 for NAS-IP-Address.
Length = 6
Address = The Address field is four octets.