252 Chapter 7: OSPF, EIGRP, and IGRP
Answer to Scenario 2
OSPF allows for linking discontiguous parts of the CIS/CIE backbone using a virtual link. In
the case of CIS and CIE, different Area 0s need to be linked because CIS and CIE need to merge
two separate OSPF networks into one network with a common Area 0. A virtual link can be
configured between separate ABRs that touch Area 0 from each side and that have a common
area. This is illustrated in Figure 7-14.
Figure 7-14
Revised CIS and CIE Topology
In Figure 7-14, two Area 0s are linked via a virtual link. In case a common area does not exist,
an additional area, such as Area 3, could be created to become the transit area between CIS
and CIE.
NOTE
Cisco recommends that virtual links be considered a temporary fix rather than a
permanent solution.
CIS
R1
CIS
R2
OSPF
Area 0
OSPF
Area 3
Virtual
link
CIE
R2
CIE
R1
OSPF
Area 0
87200333.book Page 252 Wednesday, August 22, 2001 2:37 PM