| 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.
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