A. Provides features for most Ethernet, Frame Relay, and dial-up network deployment types.
B. Provides routing for IPv4, IPv6, Appletalk, and IPX.
C. Provides default hierarchical routing and summarization of a VLSM IP address deployment.
D. Provides quick convergence through neighbor relationships and topology backup routes.
E. Provides the best route selection on combined default metrics of active bandwidth, delay, load, reliability, and MTU parameters.
Correct Answer: BD
EIGRP is sometimes referred to as a hybrid routing protocol because it has characteristics of both distance-vector and link-state protocols. For example, EIGRP
doesn’t send link-state packets as OSPF does; instead, it sends traditional distance-vector updates containing information about networks plus the cost of
reaching them from the perspective of the advertising router. And EIGRP has link-state characteristics as well-it synchronizes routing tables between neighbors at
startup, and then sends specific updates only when topology changes occur. This makes EIGRP suitable for very large networks. EIGRP has a maximum hop
count of 255. There are a number of powerful features that make EIGRP a real standout from IGRP and other protocols.
The main ones are listed here:
Support for IP, IPX, and AppleTalk via protocol-dependent modules.
Considered classless (same as RIPv2 and OSPF)
Support for VLSM/CIDR
Support for summaries and discontiguous networks
Efficient neighbor discovery
Communication via Reliable Transport Protocol (RTP)
Best path selection via Diffusing Update Algorithm (DUAL)
One of the most interesting features of EIGRP is that it provides routing support for multiple Network layer protocols: IP, IPX, and AppleTalk. The only
other routing protocol that comes close and supports multiple network layer protocols is Intermediate System-to-Intermediate System (IS-IS), but it only supports
IP and Connectionless Network Service (CLNS). EIGRP supports different Network layer protocols through the use of protocol-dependent modules (PDMs). Each
EIGRP PDM will maintain a separate series of tables containing the routing information that applies to a specific protocol. What this means to you is that there will
be IP/EIGRP tables, IPX/EIGRP tables, and AppleTalk/EIGRP tables.
EIGRP for IPv4 Summary
The characteristics of EIGRP for IPv4 networks follow:
■ Hybrid routing protocol (a distance-vector protocol that has link-state protocol characteristics).
■ Uses IP protocol number 88.
■ Classless protocol (supports VLSMs).
■ Default composite metric uses bandwidth and delay.
■ You can factor load and reliability into the metric.
■ Sends partial route updates only when there are changes.
■ Supports MD5 authentication.
■ Uses DUAL for loop prevention.
■ Fast convergence.
■ By default, equal-cost load balancing with equal metrics. Unequal-cost load sharing with the variance command.
■ Administrative distance is 90 for EIGRP internal routes, 170 for EIGRP external routes, and 5 for EIGRP summary routes.
■ High scalability; used in large networks.
■ Multicasts updates to 188.8.131.52.
■ Does not require a hierarchical physical topology.
■ Provides routing for IPv4, plus legacy protocols such as AppleTalk and IPX.
EIGRP implements DUAL to select paths and guarantee freedom from routing loops. J. J. Garcia Luna-Aceves developed DUAL. It is mathematically proven to
result in a loop-free topology, providing no need for periodic updates or route hold-down mechanisms that make convergence slower. DUAL selects a best path
and a second-best path to reach a destination. The best path selected by DUAL is the successor, and the second-best path (if available) is the feasible
successor. The feasible distance is the lowest calculated metric of a path to reach the destination.