CCNA 3

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CCNA 3

• Module 3 Review

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3.1.1 Comparing EIGRP with IGRP

• Redistribution, the sharing of routes, is
  automatic between IGRP and EIGRP as long as both
  processes use the identical autonomous system
  (AS) number.
• EIGRP and IGRP use different metric calculations.
  EIGRP scales the metric of IGRP by a factor of
  256. That is because EIGRP uses a metric that is
  32 bits long, and IGRP uses a 24-bit metric.

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3.1.2 EIGRP Concepts and Terminology

• Routes denoted by EX in Routing Table entries
• External routes originate outside the EIGRP AS.
• Routes learned or redistributed from other
  routing protocols, such as Routing Information
  Protocol (RIP), OSPF, and IGRP, are external.
• The EIGRP DUAL algorithm stores the primary route
  to the destination in the routing table and the
  topology table.
• A feasible successor (FS) is a backup route.

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3.1.2 EIGRP Concepts and Terminology

• EIGRP default administrative distance for
  internal routes is 90
• Information maintained by the EIGRP topology
  database about a destination route
• Routing Protocol
• Feasible distance of the route
• Route cost as advertised by the neighboring
  router

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3.1.3 EIGRP Design Features

• EIGRP makes efficient use of bandwidth by sending
  partial, bounded updates only to the routers that
  need the information, not to all routers in an
  area.
• They can support multiple routed protocols.
• They use hello packets to inform neighboring
  routers of their status.

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3.1.3 EIGRP Design Features

• EIGRP maintains numerous tables for each routed
  protocol it supports.
• Topology table
• Neighbor table
• Routing table

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3.1.3 EIGRP Design Features

• EIGRP advantages in forming adjacencies
• New routers and routes are quickly discovered by
  neighbors routers.
• A router can quickly discover when a neighbor
  router is no longer available.
• Changes in network topology can be quickly shared
  with neighbor routers.

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3.1.4 EIGRP Technologies

• Reliable Transport Protocol (RTP) is a
  transport-layer protocol that can guarantee
  ordered delivery of EIGRP packets to all
  neighbors.

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3.2.1 Configuring EIGRP

• When configuring serial links using EIGRP, it is
  important to configure the bandwidth setting on
  the interface.
• If the bandwidth for these interfaces is not
  changed, EIGRP assumes the default bandwidth on
  the link instead of the true bandwidth.
• If the link is slower, the router may not be able
  to converge, routing updates might become lost,
  or suboptimal path selection may result.

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3.2.2 Configuring EIGRP Summarization

• If there are discontiguous subnetworks
  auto-summarization must be disabled for routing
  to work properly. To turn off
  auto-summarization, use the following command
• router(config-router)no auto-summary

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3.2.2 Configuring EIGRP Summarization
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3.2.3 Verifying basic EIGRP
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3.2.4 Building Neighbor Tables

• The following fields are found in a neighbor
  table
• Neighbor address This is the network layer
  address of the neighbor router.
• Hold time This is the interval to wait without
  receiving anything from a neighbor before
  considering the link unavailable. Originally, the
  expected packet was a hello packet, but in
  current Cisco IOS software releases, any EIGRP
  packets received after the first hello will reset
  the timer.
• Smooth Round-Trip Timer (SRTT) This is the
  average time that it takes to send and receive
  packets from a neighbor. This timer is used to
  determine the retransmit interval (RTO).

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3.2.4 Building Neighbor Tables

• The following fields are found in a neighbor
  table
• Queue count (Q Cnt) This is the number of
  packets waiting in a queue to be sent. If this
  value is constantly higher than zero, there may
  be a congestion problem at the router. A zero
  means that there are no EIGRP packets in the
  queue.
• Sequence Number (Seq No) This is the number of
  the last packet received from that neighbor.
  EIGRP uses this field to acknowledge a
  transmission of a neighbor and to identify
  packets that are out of sequence. The neighbor
  table is used to support reliable, sequenced
  delivery of packets and can be regarded as
  analogous to the TCP protocol used in the
  reliable delivery of IP packets.

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3.2.6 Select routes

• If a feasible successor is not found, DUAL flags
  the route as Active, or unusable at present.

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3.3.1 Routing Protocol Troubleshooting Process

• show commands help monitor installation behavior
  and normal network behavior, as well as isolate
  problem areas.
• debug commands assist in the isolation of
  protocol and configuration problems not
  associated with normal network behavior.
• Trace command can be used to identify bottlenecks
  or broken network connections.

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3.3.3 Troubleshooting IGRP Configuration

• Use the router igrp autonomous-system command to
  enable the IGRP routing process
• R1(config)router igrp 100
• Verify IGRP configuration with the show
  running-configuration and show ip protocols
  commands
• R1show ip protocols
• Verify IGRP operation with the show ip route
  command
• R1show ip route

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3.3.3 Troubleshooting IGRP Configuration

• If a network becomes inaccessible, routers
  running IGRP send triggered updates to neighbors
  to inform them. A neighbor router will then
  respond with poison reverse updates and keep the
  suspect network in a holddown state for 280
  seconds. 

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3.3.4 Troubleshooting EIGRP configuration

• Router show ip route eigrp
• Displays only the current EIGRP routing table
  entries

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3.3.5 Troubleshooting OSPF Configuration

• The show ip ospf neighbor command is useful for
  troubleshooting adjacency formation.