The four name server address configuration options, 129 to 132, provide a method of obtaining the addresses of Domain Name System (DNS) servers and (NetBIOS Name Server (NBNS) nodes on the remote network.
Primary and secondary addresses are negotiated independently. They serve identical purposes, except that when both are present an attempt SHOULD be made to resolve names using the primary address before using the secondary address.
For implementational convenience, these options are designed to be identical in format and behavior to option 3 (IP-Address) which is already present in most IPCP implementations.
Since the usefulness of name server address information is dependent on the topology of the remote network and local peer's application, it is suggested that these options not be included in the list of "IPCP Recommended Options".