CCNA/Networking

Routing ProtocolsRouting Protocols
Nettech India @ 9870803004/5

OBJECTIVES
Differentiate between nonroutable, routed, and routing protocols
Define Interior Gateway Protocols, Exterior Gateway Protocols, distance-vector
routing protocols, and link-state routing protocols
Explain the concepts of count-to-infinity, split horizon, split horizon with poison
reverse, and hold-down timers
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OBJECTIVES (CONTINUED)
Describe, configure, and monitor the interior routing protocol RIP
Explain static routing and administrative distance
Configure static routing and default routes
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NONROUTABLE PROTOCOLS
In the early days of networking, networks were small collections of computers
linked together
 For the purposes of sharing information and expensive peripherals
Early networks were sometimes configured as peer-to-peer networks
 Computers communicate with and provide services to their “peers”
 All communication occurs on the same network segment
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NONROUTABLE PROTOCOLS (CONTINUED)
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NONROUTABLE PROTOCOLS (CONTINUED)
Several nonroutable protocols exist in today’s networking world
NetBEUI (NetBIOS Enhanced User Interface)
 The most common nonroutable protocol
 Ships with all Microsoft Windows operating systems
NetBEUI cannot scale into large internetworks
 Cannot hold Network layer information in its network header
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ROUTED PROTOCOLS
Routed protocols
 Have packet headers that can contain Network layer addresses
 Developed to support networks consisting of multiple networks or subnetworks
Protocols that can carry Network layer information
 Transmission Control Protocol/Internet Protocol (TCP/IP)
 Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)
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ROUTED PROTOCOLS (CONTINUED)
For routed protocols to work on a network
 Every device must be configured with a unique IP or IPX address (logical address)
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ROUTING PROTOCOLS
Routing protocols
 Protocols used by routers to make path determination choices and to share those choices
with other routers
Hop count
 The number of routers a packet must pass through to reach a particular network
Metric
 A value used to define the suitability of a particular route
 Routers use metrics to determine which routes are better than other routes
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ROUTING PROTOCOLS (CONTINUED)
Autonomous system (AS)
 Uses Interior Gateway Protocols as routing protocols
 A group of routers under the control of a single administration
Interior Gateway Protocols (IGPs) are
 Routing protocols used within an AS
Exterior Gateway Protocols (EGPs)
 Routing protocols used to route information between multiple autonomous systems
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Examples of IGPs
 Routing Information Protocol (RIP)
 Interior Gateway Routing Protocol (IGRP)
 Enhanced Interior Gateway Routing Protocol (EIGRP)
 Open Shortest Path First (OSPF)
Example of EGP
 Border Gateway Protocol (BGP)
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TWO TYPES OF IGPS
Distance-vector routing protocols
 Broadcast their entire routing table to each neighbor router at predetermined intervals
 The actual interval depends on the distance-vector routing protocol in use
 Varies between 30 and 90 seconds
 Sometimes referred to as routing by rumor
 Suffer from slow time to convergence
 A state where all routers on the internetwork share a common view of the internetwork
routes
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TWO TYPES OF IGPS (CONTINUED)
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Distance-vector routing protocols (continued)
 Routing loops
 Often referred to as count-to-infinity problems
 Loops, without preventive measures, will cause packets to bounce around the
internetwork infinitely
 Defining a maximum
 One of the easiest ways to limit count-to-infinity problems
 Split horizon and split horizon with poison reverse
 Two other common ways to prevent routing loops when using distance-vector routing
protocols
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Nettech Indiaisco Networking
Fundamentals,
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Distance-vector routing protocols (continued)
 Hold-down timer
 Another common technique used to stop routing loops
 Allow a router to place a route in a state where it will not accept any changes to that route
Link-state routing protocols
 Use link-state advertisements (LSAs) to inform neighbor routers on the internetwork
 LSAs contain only the local links for the advertised router
CCNA GUIDE TO CISCO NETWORKING FUNDAMENTALS, FOURTH EDITION 21

Link-state routing protocols (continued)
 Shortest Path First (SPF) algorithm
 Uses the link information to compute the routes
 Router CPU resources are used instead of bandwidth
 Link-state packets (LSPs)
 Packets used to send out LSAs
 Allow every router in the internetwork to share a common view of the topology of the
internetwork
 A link-state routing protocol floods, or multicasts, LSPs to the network
 Later updates will be triggered updates
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Link-state routing protocols (continued)
 Routers using link-state protocols must be configured with more memory and processing
power
 Than those using distance-vector routing protocols
 Link-state routing protocols such as OSPF are much more complicated to configure on the
routers
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ROUTING INFORMATION PROTOCOL
Routing Information Protocol (RIP)
 The easiest Interior Gateway Protocol to configure is RIPv1
 A distance-vector routing protocol that broadcasts entire routing tables to neighbors every
30 seconds
 RIP uses hop count as its sole metric
RIP has a maximum hop count of 15
 As a result, RIP does not work in large internetworks
RIP is capable of load balancing
RIP is susceptible to all the problems normally associated with distance-vector
routing protocols
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ENABLING RIP ROUTING
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ENABLING RIP ROUTING (CONTINUED)
To start configuring RIP, you must:
 Enter privileged mode first
 Enter global configuration mode on your router
Enable RIP with the router rip command
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CONFIGURING RIP ROUTING FOR EACH MAJOR
NETWORK
network command
 Turns on RIP routing for a network
 An individual network command must be issued for each separate network directly
connected to the router
show ip route command
 Displays a router’s routing table
Administrative distance
 A value used to determine the reliability of the information regarding a particular route
 Administrative distances range from 0–255
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NETWORK (CONTINUED)
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NETWORK (CONTINUED)
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SHOW IP PROTOCOL AND DEBUG IP RIP
COMMANDS
Commands used to monitor RIP
A route is considered invalid if six consecutive update intervals pass without an
update from that route
Flush interval
 The time at which a route will be totally removed from the routing table if no updates are
received
debug ip rip command
 Displays real-time rip updates being sent and received and places very high processing
demands on your router, which could affect network performance
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COMMANDS (CONTINUED)
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INTERIOR GATEWAY ROUTING PROTOCOL
IGRP is a proprietary distance-vector routing protocol
 Created by Cisco to solve some of the problems associated with RIP
A larger hop-count metric allows IGRP to be used on larger networks
 IGRP supports a hop count of 255, although 100 is the default if hop count is configured to
be used as a metric
The metric maximum-hops command allows you to set the maximum hop count
for IGRP
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INTERIOR GATEWAY ROUTING PROTOCOL
(CONTINUED)
The default metrics for IGRP are bandwidth and delay only
Metrics that can be configured for IGRP
 Hops: number of routers between source and destination networks
 Load: the load on a link in the path
 Bandwidth: the speed of the link (default)
 Reliability: measures reliability with a scale of 0 to 255
 Delay: the delay on the medium (default)
 MTU: the size of the datagram
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STATIC ROUTING
Some networks are so small that using a routing protocol creates:
 Unnecessary traffic
 An inefficient use of router processor resources
• Stub routers
 Routers with only one route out
 Stub routers are usually the last router in a chain
Stub networks
 Networks with one route to the Internet
Static routes are configured by a network administrator using the ip route
command
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ADDING STATIC ROUTES
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ADDING STATIC ROUTES (CONTINUED)
Syntax for the ip route command:
ip route [destination network address] [destination network mask]
[ip address next hop interface] [administrative distance]
Examples:
ip route 172.32.3.0 255.255.255.0 172.32.2.2
ip route 172.32.4.0 255.255.255.0 172.32.2.2
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Changing administrative distance
 The ip route command allows you to configure an administrative distance
 Unless you add an administrative distance value to the end of your ip route command
 The administrative distance will be 1
Configuring a default route
 All packets that are not defined specifically in your routing table will go to the specified
interface for the default route
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Configuring a default route (continued)
 A default route is a type of static route that the administrator configures
 You can use the ip default-network command or the ip route 0.0.0.0
0.0.0.0 command to configure a default route
 Default routes are sometimes called quad zero routes
 A default route is used only if no other route to a network exists in the routing table
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SUMMARY
Some protocols are designed to be used in small networks without the need
for Network layer addressing
The most common nonroutable protocol is NetBEUI
Other protocols were designed with the ability to move between multiple
networks via Network layer addressing
The most common routed protocol suite is TCP/IP
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SUMMARY (CONTINUED)
Protocols must be available that can find the best path throughout an
internetwork and relay that information to routers
Routing protocols are classed in two major groups: Interior Gateway Protocols
and Exterior Gateway Protocols
Interior routing protocols are further divided into distance-vector and link-
state routing protocols
These two types of Interior Gateway Protocols use very different methods to
determine the best path in an internetwork
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SUMMARY (CONTINUED)
Distance-vector protocols periodically broadcast entire routing tables to
neighbor routers
Link-state protocols multicast link updates to routers in their area upon
startup and when network topology changes
Two common distance-vector IGPs discussed in this chapter are the Routing
Information Protocol and the Interior Gateway Routing Protocol
Static routes are used to conserve bandwidth and lower memory and CPU
load on a router while still allowing for correct routing table creation
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CCNA/Networking

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