IP Routing

Route Summarization

Consider the router Phoenix, which connects to SantaFe and sends the RIP updates shown earlier:

192.100.1.48
192.100.1.64
192.100.2.0
10.0.0.0

Phoenix may have been configured as follows (see Figure 2-8, later in Chapter 2):

hostname Phoenix
ip subnet-zero
!
interface Ethernet 0
ip address 192.100.1.18 255.255.255.240
!
interface Ethernet 1
ip address 192.100.1.49 255.255.255.240
!
interface Ethernet 2
ip address 192.100.1.65 255.255.255.240
!
interface Ethernet 3
ip address 192.100.2.1 255.255.255.240
!
interface Ethernet 4
ip address 192.100.2.17 255.255.255.240
!
interface Ethernet 5
ip address 10.1.0.1 255.255.0.0
!
interface Ethernet 6
ip address 10.2.0.1 255.255.0.0
!
router rip
network 192.100.1.0
network 192.100.2.0
network 10.0.0.0

Phoenix did not send detailed routes for 192.100.2.0 or 10.0.0.0 when advertising to SantaFe because Phoenix summarized those routes. As I stated earlier, since Phoenix did not have interfaces on those networks, it couldn’t have made sense of those routes anyway.