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424 Chapter 11: Remote Access
Answer to Scenario 1
There are other ways of meeting the company's requirements. This is only a recommended
solution that meets the requirements placed on the network architect.
Figure 11-20 depicts a recommended solution. There are six branch sites at the bottom of the
figure. The branch sites each have a Frame Relay connection to their regional office. If the
Frame Relay link should fail, the ISDN Link will come up and connect them to their respective
regional office. What if a catastrophe hits the regional office in Dallas, for example? Let's take
a look at what happens:
·
The branch office Irving loses its Frame Relay connection to the regional office.
·
The ISDN link kicks in and calls the Dallas regional office.
·
The Dallas regional office is not there to respond.
Figure 11-20
Scenario 1 Suggested Solution
The customer's requirement that the branch office be able to survive a regional office outage
can be met with the IP unnumbered feature. If you implement this feature with the routing
protocol EIGRP, you can configure the branch office to dial in to any regional office. And the
BRI interface can actually be configured to try different regional offices.
For example, suppose the Atlanta region has an outage. The Nashville router first attempts to
dial into Atlanta. After receiving no response, the Nashville router dials into Dallas and gets an
answer. The EIGRP protocol forms a neighbor relationship, and for 30 to 35 seconds the route
to Nashville is known to the rest of the network as going through Dallas.
Cloud
Regional
Headquarters
Branch site
Cloud
Regional
Branch site
87200333.book Page 424 Wednesday, August 22, 2001 2:53 PM