1.2 Overview of Scalable Internetworks
1.2.6 Making the network adaptable
Because scalable internetworks experience change frequently, they must be able to adapt to changes, such as the following:

Mixing routable and nonroutable protocols --- A network delivering both routable and nonroutable traffic has some unique problems. Routable protocols can be forwarded from one network to another based on a network-layer address (such as an IP address). Nonroutable protocols do not contain any network-layer address and cannot be forwarded by routers. Most nonroutable protocols also lack a mechanism to provide flow control and are sensitive to delays in delivery. Any delays in delivery or packets arriving out of order can result in session loss.

Integrating "islands" of networks --- Many companies are integrating islands of networks that are typically using different protocols in their hierarchical design. In this case, you can add any protocols used by the network islands to the core layer, or create a tunnel in the backbone that will connect the network islands but not add new protocol traffic to the core backbone.

Meet the varying requirements for each protocol in the internetwork --- When multiple protocol traffic is present, the network must be balanced between the special needs of each protocol.

Cisco IOS features that focus on network adaptability include:

EIGRP --- This routing protocol supports IP, IPX, and AppleTalk traffic.

Redistribution --- You can exchange routing information between networks that are using different routing protocols. Route redistribution is a key feature in Cisco routers. Mastering the usage of route redistribution is important to enable different protocols to communicate with each other successfully.