1. A method comprising: receiving, with a network device, a routing protocol message that advertises a link, wherein the routing protocol message includes a field for storing first data associated with the link in accordance with the routing protocol, and wherein the field is defined by the routing protocol as a type of field having a different function from an administrative group field as defined by the same routing protocol; determining, with the network device, that the field of the received routing protocol message has been repurposed to store second data in addition to the first data, wherein the second data specifies one or more extended administrative groups for the link different from the one or more administrative groups that are to be specified by the administrative group field; upon determining that the field has been repurposed, updating routing information to associate the advertised link with the one or more extended administrative groups specified by the second data; and performing, with the network device, path selection to select one or more paths based on the updated routing information.