Providing extended administrative groups in computer networks

In general, techniques are described for providing extended administrative groups in networks. A network device comprising an interface and a control unit may implement the techniques. The interface receives a routing protocol message that advertises a link. This message includes a field for storing first data associated with the link in accordance with the routing protocol. The field is defined by the routing protocol as a field having a different function from an administrative group field defined by the same routing protocol. The control unit determines that this field has been repurposed to store second data, wherein this second data specifies an extended administrative group for the link different from those that may be specified by the administrative group field. The control unit then updates routing information to associate the advertised link with the extended administrative group and performs path selection to select paths based on the updated routing information.