Seville, as seen in its update received into Albuquerque's serial 1 interface. In fact, the debug
output looks exactly like it would have earlier, when subnet 10.1.3.0/24 was used on Seville's
Ethernet, if that Ethernet was down. However, in this case, the Ethernet is up, as shown in the
show ip route output from Seville at the end of Example 6-6. Essentially, RIP will not advertise
the route with a mask of 255.255.255.192 out an interface that is in the same network but that
has a different mask. If RIP on Seville had advertised the route to 10.1.3.192, Albuquerque and
Yosemite would have believed there was a problem because the subnet number is 10.1.3.192,
which is not a subnet number with the mask that Albuquerque and Yosemite think is in use
(255.255.255.0). So, RIP and IGRP simply do not advertise the route into the same network on
an interface that uses a different mask. The use of different masks in parts of the same network
is called variable-length subnet masking (VLSM). As seen in this example, VLSM is not
supported by RIP (Version 1) or IGRP.
ip addr 10.1.2.252 255.255.255.0
interface serial 0
ip addr 10.1.4.252 255.255.255.0
interface serial 1
ip address 10.1.2.252 255.255.255.0
network 10.0.0.0
ip addr 10.1.3.253 255.255.255.192
interface serial 0
ip addr 10.1.6.253 255.255.255.0
interface serial 1
ip address 10.1.5.253 255.255.255.0
!
router rip
network 10.0.0.0