1.2 Key Characteristics of Scalable Internetworks
1.2.6 Making the network adaptable
An adaptable network can gracefully handle the addition and coexistence of multiple routed and routing protocols. EIGRP is an exceptionally adaptable protocol because it supports routing information for three routed protocols: IP, IPX, and AppleTalk.

The Cisco IOS also supports route redistribution, which is described in Chapter 7, Route Optimization. Route redistribution allows routing information to be shared (i.e., redistributed) among two or more different routing protocols. For instance, RIP routes can be redistributed into an OSPF area.

Mixing routable and non-routable protocols
A network delivering both routable and non-routable traffic has some unique problems. Routable protocols (e.g., IP) can be forwarded from one network to another based on a network-layer address. Non-routable protocols (e.g., SNA) do not contain any network-layer address and cannot be forwarded by routers. Most non-routable 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. An adaptable network should accommodate both routable and non-routable protocols.