CCNA 3 Labs and Study Guide - BINARYBB.INFO – @jagalbraith

Vocabulary Exercise: Completion
Directions: Complete the paragraphs that follow by filling in appropriate words and phrases.
IGRP and EIGRP are compatible with each other, which provides seamless interoperability between the
two processes. EIGRP uses metric calculations similar to those used by IGRP, and EIGRP supports the
same unequal-cost path load balancing as IGRP does.
Although the metric (bandwidth and delay by default) is the same for both IGRP and EIGRP, the weight
assigned to the metric is 256 times greater for EIGRP. That is because EIGRP uses a metric that is 32 bits
long, and IGRP uses a 24-bit metric. By multiplying or dividing by 256, EIGRP can easily exchange information
with IGRP.
IGRP has a maximum hop count of 255. EIGRP has a maximum hop count of 224. By default, the Cisco
IOS limits the hop count for EIGRP limited to 100 as displayed by the show ip protocols command. This
is more than adequate to support the largest, properly designed internetworks.
EIGRP’s convergence technology employs the Diffusing Update Algorithm (DUAL), which guarantees
loop-free operation at every instant throughout a route. Routers that are not affected by topology changes
are not involved in recomputations.
Redistribution, the sharing of routes, is automatic between IGRP and EIGRP as long as both processes use
the same autonomous system number.
Like OSPF, EIGRP maintains three tables for use with its computations. These tables include the neighbor
table (called the adjacency database in OSPF), the topology table (called the link-state database in OSPF),
and the routing table (called the forwarding database in OSPF).
The following are some additional features of EIGRP:
■ EIGRP converges rapidly on network topology changes. In some situations, convergence can be
almost instantaneous. EIGRP stores backup routes, called feasible successors, so that it can quickly
adapt to these alternate routes if the primary route, called the successor, becomes unavailable. If no
backup route exists, then EIGRP sends a query packet to its neighbors to discover an alternate route.
■ During normal operations when the network topology is fully converged, only hello packets are sent
to neighbors. These packets are also used to establish neighbor adjacencies.
■ EIGRP supports automatic route summarization at classful network boundaries. But it can be manually
configured to advertise on arbitrary network boundaries to reduce the size of routing tables.
■ EIGRP uses its own Layer 4 protocol called the Reliable Transport Protocol. Because EIGRP provides
support for multiple routed protocols, including AppleTalk (AT) and Internetwork Packet Exchange
(IPX), it must be protocol independent. That means it cannot depend on TCP for reliability services.
EIGRP Packet Type Exercise
Like OSPF, EIGRP relies on different types of packets to maintain its tables and establish relationships
with neighbor routers. Complete the missing elements that follow by filling in appropriate words or phrases.
When given the choice, circle whether the packet is reliable or unreliable and whether it is unicast or
multicast.
Hello packets:
■ (Reliable/Unreliable) (unicast/multicast) sent to the address 224.0.0.10 to discover and maintain
neighbors; contains the router’s neighbor table
■ Default hello interval depends on the bandwidth:
— ≤ 1.544 Mbps = 60 sec. hello interval (180 sec. holdtime)
— > 1.544 Mbps = 5 sec. hello interval (15 sec. holdtime)
Chapter 3: EIGRP and Troubleshooting Routing Protocols 177