Classful routing protocols cannot send supernet routes. This is because the receiving router automatically applies the default classful subnet mask to the network address in the routing update. If the topology in the figure contained a classful routing protocol, then R3 would only install 172.16.0.0/16 in the routing table.
Propagating VLSM and supernet routes requires a classless routing protocol such as RIPv2, OSPF, or EIGRP. Classless routing protocols advertise network addresses with their associated subnet masks. With a classless routing protocol, R2 can summarize networks 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16, and 172.19.0.0/16, and advertise a supernet summary static route 172.16.0.0/14 to R3. R3 then installs the supernet route 172.16.0.0/14 in its routing table.
Note: When a supernet route is in a routing table, for example, as a static route, a classful routing protocol does not include that route in its updates.