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Transcript
CCNA 2 Module 6
Routing and Routing Protocols
© 2003, Cisco Systems, Inc. All rights reserved.
1
Objectives
• Introduction to static routing
• Dynamic routing overview
• Routing protocols overview
© 2003, Cisco Systems, Inc. All rights reserved.
2
Overview
• Routing is a set of directions to get from one network to
another.
• These directions are known as routes
• Routes can be dynamically given to the router by
another router
• (or) Route can be statically assigned to the router by
an administrator.
• A network administrator chooses a dynamic routing
protocol based upon many considerations.
– the size of the network, the bandwidth of available
links, the processing power of the routers, the brands
and models of the routers
© 2003, Cisco Systems, Inc. All rights reserved.
3
Introduction to Routing: Route Types
• Routing is the process that a router uses to forward
packets toward the destination network.
• A router makes decisions based upon the destination
IP address of a packet.
• To make the correct decisions, routers must learn how
to reach remote networks.
© 2003, Cisco Systems, Inc. All rights reserved.
4
Specifying Outgoing Interface (First command)
© 2003, Cisco Systems, Inc. All rights reserved.
5
Specifying the Next-hop IP Address (Second
Command)
© 2003, Cisco Systems, Inc. All rights reserved.
6
Specifying the Next-hop IP Address
Continued
• The administrator could enter either of two commands to
accomplish this objective: specifies the outgoing interface or
specifies the next-hop IP address of the adjacent router.
• The only difference between the two is in the administrative
distance assigned to the route by the router as it is placed in
the routing table
• The administrative distance is an optional parameter that gives
a measure of the reliability of the route.
• A lower value for the administrative distance indicates the
more reliable route.
• Thus, a route with a lower administrative distance will be
installed before an identical route with a higher administrative
distance.
© 2003, Cisco Systems, Inc. All rights reserved.
7
Specifying the Next-hop IP Address
Continued
• The default administrative distance when using next-hop
address is 1, while the default administrative distance
when using the outgoing interface is 0.
• If an administrative distance other than the default is
desired, a value between 0 - 255 is entered after the
next-hop or outgoing interface as follows:
• waycross(config)#ip route 172.16.3.0
255.255.255.0 172.16.4.1 130
• To use a static route as a backup, set a higher
administrative distance than the dynamic routing
protocol.
© 2003, Cisco Systems, Inc. All rights reserved.
8
Configuring Static Routes
© 2003, Cisco Systems, Inc. All rights reserved.
9
Use a Local Interface as a Gateway
© 2003, Cisco Systems, Inc. All rights reserved.
10
Using a Next-Hop Device
© 2003, Cisco Systems, Inc. All rights reserved.
11
Non-directly Connected Networks (Default Route)
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12
Verifying Static Route Configuration
• The command show running-config is
used to view the active configuration in RAM
to verify that the static route was entered
correctly.
• The show ip route command is used to
make sure that the static route is present in
the routing table
© 2003, Cisco Systems, Inc. All rights reserved.
13
Verifying Static Route Configuration
Continued
© 2003, Cisco Systems, Inc. All rights reserved.
14
Troubleshooting Static Route Configuration
• The show ip route command
• The ping command
• The traceroute command
© 2003, Cisco Systems, Inc. All rights reserved.
15
Routed Versus Routing Protocol
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16
Routed Versus Routing Protocol
Continued
• A routing protocol allows one router to share information
with other routers regarding the networks it knows about.
• The information a router gets from another router, using a
routing protocol, is used to build and maintain a routing
table.
• A routed protocol provides enough information to allow a
packet to be forwarded from one host to another based
on the addressing scheme
© 2003, Cisco Systems, Inc. All rights reserved.
17
Autonomous Systems
• An autonomous system (AS) is
a collection of networks under a
common administration sharing
a common routing strategy.
• The American Registry of
Internet Numbers (ARIN), a
service provider, or an
administrator assigns an
identifying number to each AS.
• This autonomous system
number is a 16 bit number.
• Routing protocols, such as Cisco’s IGRP, require assignment
of a unique, autonomous system number.
© 2003, Cisco Systems, Inc. All rights reserved.
18
Dynamic Routing Operations
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19
Purpose of Routing Protocol
• The goal of a routing protocol is to build and
maintain a routing table.
• This table contains the learned networks and
associated ports for those networks.
• Routers use routing protocols to manage information
received from other routers and its interfaces.
• The routing protocol learns all available routes,
places the best routes into the routing table, and
removes routes when they are no longer valid.
• The router uses the information in the routing table
to forward routed protocol packets.
© 2003, Cisco Systems, Inc. All rights reserved.
20
Purpose of Routing Protocol
• The routing algorithm is fundamental to dynamic
routing.
• Whenever the topology of a network changes
because of growth, reconfiguration, or failure, the
network knowledgebase (routing table) must also
change.
• The network knowledgebase needs to reflect an
accurate view of the new topology.
© 2003, Cisco Systems, Inc. All rights reserved.
21
Dynamic Routing Operations
Continued
• When all routers in an internetwork are operating
with the same knowledge, the internetwork is said to
have converged.
• Fast convergence is desirable because it reduces
the period of time in which routers would continue to
make incorrect routing decisions.
© 2003, Cisco Systems, Inc. All rights reserved.
22
Classes of Routing Protocols
• The distance vector routing approach determines the
direction (vector) and distance to any link in the internetwork.
• The link-state routing approach , also called shortest path
first, recreates the exact topology of the entire internetwork.
© 2003, Cisco Systems, Inc. All rights reserved.
23
Distance Vector Concepts
• Distance vector based routing algorithms are also known as
Bellman-Ford algorithms
© 2003, Cisco Systems, Inc. All rights reserved.
24
Distance Vector Concepts
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25
Distance Vector Concepts
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26
Routing Metric Components
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27
Link-State Concepts
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28
Link-State Concepts
Continued
• Link-state algorithms are also known as Dijkstras
algorithm or as SPF (shortest path first) algorithms.
• Link-state routing uses:
• Link-state advertisements (LSAs) – A link-state
advertisement (LSA) is a small packet of routing
information that is sent between routers.
• Topological database – A topological database is a
collection of information gathered from LSAs.
• SPF algorithm – The shortest path first (SPF) algorithm
is a calculation performed on the database resulting in
the SPF tree.
• Routing tables – A list of the known paths and
interfaces.
© 2003, Cisco Systems, Inc. All rights reserved.
29
Link-State Network Discovery
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30
Link-State Topology Changes
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31
Link-State Concerns
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32
Path Determination
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33
Routing with Network Addressing
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34
IP Routing Configuration Tasks
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35
Using the router and network
Commands
• An example of a routing configuration is:
GAD(config)#router rip
GAD(config-router)#network 172.16.0.0
© 2003, Cisco Systems, Inc. All rights reserved.
36
Routing Protocols: Interior and Exterior Routing
Protocols
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37
Routing Protocols
Continued
• Examples of IP routing protocols include:
• RIP – A distance vector interior routing protocol
• IGRP – Cisco's distance vector interior routing
protocol
• OSPF – A link-state interior routing protocol
• EIGRP – Cisco’s advanced distance vector
interior routing protocol
• BGP – A distance vector exterior routing protocol
© 2003, Cisco Systems, Inc. All rights reserved.
38
Routing Protocols
RIP
• Routing Information Protocol (RIP) was
originally specified in RFC 1058. Its key
characteristics include the following:
• It is a distance vector routing protocol.
• Hop count is used as the metric for path
selection.
• If the hop count is greater than 15, the packet
is discarded.
• Routing updates are broadcast every 30
seconds, by default.
© 2003, Cisco Systems, Inc. All rights reserved.
39
Routing Protocols
IGRP
• Interior Gateway Routing Protocol (IGRP) is a
proprietary protocol developed by Cisco.
Some of the IGRP key design characteristics
emphasize the following:
• It is a distance vector routing protocol.
• Bandwidth, load, delay and reliability are
used to create a composite metric.
• Routing updates are broadcast every 90
seconds, by default.
© 2003, Cisco Systems, Inc. All rights reserved.
40
Routing Protocols
OSPF
• Open Shortest Path First (OSPF) is a
nonproprietary link-state routing protocol. The
key characteristics of OSPF are as follows:
• It is a link-state routing protocol.
• Open standard routing protocol described in
RFC 2328.
• Uses the SPF algorithm to calculate the
lowest cost to a destination.
• Routing updates are flooded as topology
changes occur.
© 2003, Cisco Systems, Inc. All rights reserved.
41
Routing Protocols
EIGRP
• EIGRP is a Cisco proprietary enhanced
distance vector routing protocol. The key
characteristics of EIGRP are as follows:
• It is an enhanced distance vector routing
protocol.
• Uses load balancing.
• Uses a combination of distance vector and linkstate features.
• Uses Diffused Update Algorithm (DUAL) to
calculate the shortest path.
• Routing updates are broadcast every 90 seconds
or as triggered by topology changes.
© 2003, Cisco Systems, Inc. All rights reserved.
42
Routing Protocols
BGP
• Border Gateway Protocol (BGP) is an exterior
routing protocol. The key characteristics of
BGP are as follows:
• It is a distance vector exterior routing
protocol.
• Used between ISPs or ISPs and clients.
• Used to route Internet traffic between
autonomous systems.
© 2003, Cisco Systems, Inc. All rights reserved.
43
Interior/Exterior Routing Protocols
© 2003, Cisco Systems, Inc. All rights reserved.
44
Interior/Exterior Routing Protocols
Continued
• Interior routing protocols are designed for use in a
network whose parts are under the control of a single
organization. The design criteria for an interior routing
protocol require it to find the best path through the
network.
• An exterior routing protocol is designed for use
between two different networks that are under the control
of two different organizations. These are typically used
between ISPs or between a company and an ISP.
© 2003, Cisco Systems, Inc. All rights reserved.
45
Summary
© 2003, Cisco Systems, Inc. All rights reserved.
46