USRobotics NETServer/8 - Manual (Page 233)

Addressing Schemes B-5
Supernetting (Advanced TCP/IP)
Because Class B Internet addresses are in short supply, larger
networks are now usually granted a contiguous block of several
Class C addresses. Unfortunately, this creates very large routing
tables since multiple Class C routes have to be defined for each
network containing more than 254 nodes. Larger routing tables
mean more work for the routers and, therefore, poorer perfor-
mance.
Traditional IP - Each class C network must have
a routing table entry
Supernetting (Classless InterDomain Routing) is a technique
that allows each of these larger networks to be represented by a
single routing table entry.
To do this, supernet addressing does something very different
from traditional TCP/IP routing (which allows only one
netmask per network). In supernet routing, each supernet can
be assigned its own netmask.
Supernetting is defined in RFC 1519.