that there is no requirement to summarize into a Class A, B, or C network. Consider the same
network in Figure 6-12. Albuquerque has eight routes to subnets of network 10.0.0.0; four of
those routes are learned from Seville. Consider the subnet, broadcast, and assignable addresses
in each of the subnets, as shown in Table 6-15.
10.1.4.0/22 (same subnet, written differently) would have a subnet broadcast address of
10.1.7.255 and assignable addresses of 10.1.4.1 to 10.1.7.254. Because 10.1.4.0/22 happens to
include all the assignable addresses of the original four subnets, a single route to 10.1.4.0/22
would be just as good as the four separate routes, assuming that the next-hop information
would be the same for each of the original four routes.
subnet rather than the individual smaller subnets. In this case, the routing protocol would
advertise 10.1.4.0/22 rather than the four individual subnets. Albuquerque's routing table will
then be smaller. EIGRP and OSPF are the only interior IP routing protocols to support route
aggregation.
network of Figure 6-12, the routers are all migrated to EIGRP. Example 6-16 shows the EIGRP
configuration on Albuquerque, EIGRP configuration on Seville, and the resulting IP routing
table on Albuquerque. (Yosemite is migrated to EIGRP as well; the configuration is not shown
because the example shows only aggregation by Seville.)
Addresses
Network 10.0.0.0
Network 172.16.0.0
No auto-summary
!
interface serial 0.1 point-to-point
ip address 172.16.1.253 255.255.255.0
frame-relay interface-dlci 901