Week6 2017(1)

© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE I Chapter 6 1
Routing with a Distance
Vector Protocol in an
Enterprise Network

© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE 1 Chapter 6 2
Objectives
 Compare and contrast a flat network and a
hierarchical routed topology.
 Configure a network using RIP (Routing Information
Protocol).
 Describe and plan a network using EIGRP (Enhanced
Interior Gateway Protocol).
 Design and configure a network using EIGRP.

Compare and Contrast a Flat Network
and a Hierarchical Routed Topology
 Enterprise hierarchy
 Combination of LAN and WAN technologies
 DMZ

Compare and Contrast a Flat Network and a
Hierarchical Routed Topology
 Traffic control
 Redundant links
 QoS
 Packet filtering

 Star and extended star topologies
 Mesh topologies
Partial mesh
Full mesh

 Building the routing table
Exit interface
Next hop
Administrative distance (trustworthiness of the information received by the router)
Check this link for
the meaning of each
entry:
http://www.ciscopress.c
om/articles/article.asp?
p=2180210&seqNum=
12

 Directly connected routes
 Static routes
 Dynamic routes

Reading a routing table
 Video link: https://youtu.be/Qoe8jvpOQhY?t=23s
This video shows how to read a routing table of a router after
executing the IOS command “show ip route”

 Advantages of static routing
Stub networks
Security
Lower overhead

 Static route configuration

 Default routes
 Gateway of Last Resort

Routing Protocol Basics
 Video link: https://youtu.be/3eO29WBKg2E
This video briefly introduces the essential protocols we will
introduce and some key concepts.

Routing Using the RIP Protocol
 Characteristics of distance vector protocols
 Hop count metric
 Advantages and disadvantages

 Characteristics of RIPv1
Automatically summarizes at classful boundary
Broadcasts routing updates every 30 seconds

 Characteristics of RIPv2
Classless
Multicasts updates
Provides authentication mechanism

 RIPv2 configuration
Basic commands
Authentication
Default route redistribution

Problem
Discontiguous subnets
Unnecessary traffic
Routing loops
Solution
No auto-summary
Passive-interface
Poisoned reverse, split horizon,
holddown timer, triggered
updates
Problems with RIP and their solutions:

 SPLIT HORIZON:
A router never sends information about a route back in same direction which is original information came,
routers keep track of where the information about a route came from. Means when router A sends update to
router B about any failure network, router B does not send any update for same network to router A in same
direction.
 ROUTE POISONING:
Router consider route advertised with an infinitive metric to have failed ( metric=16) instead of marking it down.
For example, when network 4 goes down, router C starts route poisoning by advertising the metric (hop count)
of this network as 16, which indicates an unreachable network. When router B receives this advertising, it
continue advertising this network with a metric of 16.
 POISON REVERSE:
 The poison reverse rule overwrites split horizon rule. For example, if router B receives a route poisoning of
network 4 from router C then router B will send an update back to router C (which breaks the split horizon rule)
with the same poisoned hop count of 16. This ensures all the routers in the domain receive the poisoned route
update.
 Notice that every router performs poison reverse when learning about a downed network. In the above example,
router A also performs poison reverse when learning about the downed network from B.
 HOLD DOWN TIMERS:
 After hearing a route poisoning, router starts a hold-down timer for that route. If it gets an update with a better
metric than the originally recorded metric within the hold-down timer period, the hold-down timer is removed and
data can be sent to that network. Also within the hold-down timer, if an update is received from a different router
than the one who performed route poisoning with an equal or poorer metric, that update is ignored. During the
hold-down timer, the “downed” route appears as “possibly down” in the routing table.
 For example, in the above example, when B receives a route poisoning update from C, it marks network 4 as
“possibly down” in its routing table and starts the hold-down timer for network 4. In this period if it receives an
update from C informing that the network 4 is recovered then B will accept that information, remove the hold-
down timer and allow data to go to that network. But if B receives an update from A informing that it can reach
network by 1 (or more) hop, that update will be ignored and the hold-down timer keeps counting.
Source: http://www.9tut.com/rip-routing-protocol-tutorial

 Verification commands
• Troubleshooting commands
• Ping for end-to-end connectivity

Describe and Plan a Network Using
EIGRP
 Enhanced Interior Gateway Routing Protocol (EIGRP)
is another distance vector routing protocol.
 Disadvantages of distance vector routing protocols

EIGRP
 Compare EIGRP and RIP

EIGRP
 Characteristics of EIGRP
Composite metric
Guaranteed loop-free operation
Bounded updates
Hello packets

Describe and Plan a Network Using EIGRP
 Neighbor table
 Topology table
 Routing table

Describe and Plan a Network Using EIGRP
 Successors and feasible successors
 External routes

EIGRP
 EIGRP neighbors and adjacencies
 Hello protocol
 EIGRP packet types

EIGRP
 EIGRP metrics and convergence
 K values
 Feasible and reported distance

Design and Configure a Network Using
EIGRP
 Basic EIGRP configuration
 Wildcard masks
 Logging neighbor changes
 Bandwidth
 Load balancing

EIGRP
 EIGRP summarization
 Parent and child routes
 Null0 interface
 Manual summarization

EIGRP
 Verification commands
 Troubleshooting commands

EIGRP
 EIGRP issues and limitations

Comparison between RIP, EIGRP and
OSPF*
 Video link: https://youtu.be/TgpjL6_W9M0
*OSPF will be introduced in the next lecture.

Summary
 Enterprise networks are hierarchical
 Networks use static and dynamic routing to move
information
 Dynamic routing protocols are classified as either
distance vector or link state
 RIP is a distance vector routing protocol. There are
differences between RIP version 1 and RIP version 2.
 EIGRP is a Cisco proprietary distance vector routing
protocol with many advanced features
 EIGRP works best if its default features are modified to
suit the routing situation

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