A method comprising: receiving, with a network device (16A, 16B), 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 (122C, 86) wherein the administrative group field comprises an administrative group type-length-value, TLV, field defined by the routing protocol to have a type portion, a length portion and a value portion, wherein the type portion of the Administrative Group TLV field identifies the first data stored by the value portion of the Administrative Group TLV field as associating the advertised link with the one or more administrative groups in accordance with the routing protocol, and wherein the field comprises a shared risk link group, SRLG, TLV field defined by the routing protocol to have a type portion, a length portion and a value portion, wherein the type portion of the SRLG TLV field identifies the second data stored by the value portion of the SRLG TLV field as associating the advertised link with a SRLG.; 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 (120C, 96); 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. receiving, with a network device (16A, 16B), 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 (122C, 86) wherein the administrative group field comprises an administrative group type-length-value, TLV, field defined by the routing protocol to have a type portion, a length portion and a value portion, wherein the type portion of the Administrative Group TLV field identifies the first data stored by the value portion of the Administrative Group TLV field as associating the advertised link with the one or more administrative groups in accordance with the routing protocol, and wherein the field comprises a shared risk link group, SRLG, TLV field defined by the routing protocol to have a type portion, a length portion and a value portion, wherein the type portion of the SRLG TLV field identifies the second data stored by the value portion of the SRLG TLV field as associating the advertised link with a SRLG.; 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 (120C, 96); 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.