Attribute Number






Allowed in


Prohibited in

Access-Accept, Access-Reject, Access-Challenge

Presence in Packet

Required, unless NAS-Port-Type is present

Maximum Iterations


The value in this attribute represents the port to which the client user is connected. It is important to note that this value is not the socket port which might identify the protocol the client is using; this value represents the actual, tangible, physical port on the NAS gear to which the client has connected.

The information passed in this value can be useful for identifying load problems or debugging connection problems, either in the NAS itself or possibly in the hunt group connected to that NAS. Most NAS vendors include special software to configure how this information is supplied and most also include special software that will generate algorithms based on the slot number of the NAS, the specific modem, and the NAS port that show call center distribution and other statistical gems.

This attribute can co-exist with the NAS-Port-Type attribute. One of the two attributes, though, must always be present in a packet.

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