Transcript CCNA 3 Module 3 Single

CCNP 1 v3.0 Module 3
Routing Overview
Cisco Networking Academy
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Objectives
• Routing – Static and Dynamic
• Default Routing
• Floating Static Routes
• Convergence
• Route Calculation
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Routing Fundamentals
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Routing Fundamentals
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Static Routing
• Static routing is useful in networks that have a
single path to any destination network.
• Static routing reduces the memory and
processing burdens on a router.
• To configure static routing on a Cisco router, use
the ip route command. This command uses
the following syntax:
Router(config)#ip route destination-prefix
destination-prefix-mask {address |
interface} [distance] [tag tag] [permanent]
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Dynamic Routing
There are several different methods of
classifying routing protocols:
1. Interior vs. Exterior
2. Distance Vector vs. Link-state
3. Classful vs. Classless
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Configuring Dynamic Routing
• Dynamic routing of TCP/IP can be implemented
using one or more protocols which are often
grouped according to where they are used.
• Routing protocols designed to work inside an
autonomous system are categorized as interior
gateway protocols (IGPs). – RIP, IGRP, EIGRP,
OSPF
• Protocols that work between autonomous
systems are classified as exterior gateway
protocols (EGPs). – BGP, ISIS
• Protocols can be further categorized as either
distance vector or link-state routing protocols,
depending on their method of operation.
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Distance Vector Routing Protocols
• Routing protocols may be classified as either
distance vector or link-state routing protocols.
These classifications describe the algorithm, or
formula, that routers use to calculate and exchange
routing information.
Distance vector routing protocols are based on the
Bellman-Ford algorithm.
Distance vector routing protocols are concerned with
the distance and vector, or direction, of destination
networks (the exiting interface).
Distance (metric) is the proximity to the destination
network which is calculated as either hop-count or
bandwidth.
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Distance Vector Routing Protocols
•
Simple distance vector routing protocols
offer two primary advantages over linkstate protocols.
1. Relatively easy to configure.
2. Generally use less memory and processing power.
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Link-state Routing Protocols
• Offer greater scalability and faster
convergence than distance vector protocols.
• Require more memory and processing power
from the router.
• Based on Dijkstra’s algorithm (OSPF).
• Builds a complete database of all the link
states of every router in its area.
• Benefits include faster convergence and
improved bandwidth utilization over distance
vector protocols.
• May overtax low-end hardware.
• Require more complex administration.
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Hybrid Routing Protocol: EIGRP
• EIGRP is considered a hybrid routing protocol
because it has characteristics of both distancevector and link-state routing protocols.
• Some of the advantages of EIGRP are:
Rapid convergence
Event-driven updates
Loop-free routing
Multiprotocol support (IPv4, IPv6, IPX)
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Default Routing
• Default routing sends packets to a configured
next-hop address (or exiting interface) if the
destination network address is not in the routing
table.
• Default routes can be configured statically or
learned dynamically through a routing protocol
(redistributed into the routing protocol).
Router(config-router)# redistribute static
Or
Router(config-router)# default-information
originate
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Default Routing Overview
200.100.50.1
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Configuring Static Default Routes
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Default Routing with IGRP
RTB(config)#ip defaut-network 207.21.20.0
To configure default routing for IGRP, use the global configuration
command, ‘ip default-network [network number]’ at the border router.
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Floating Static Routes
• Floating static routes are static routes that are
configured with a higher administrative distance
then the routing protocol being used on the
router.
• Floating static routes are used as a backup route
to a route that is already known by the router
through a routing protocol.
• The floating static route will not show up in the
routing table until the same route known by the
routing protocol goes down.
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Administrative Distances
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Configuring Floating Static Routes
Backup Route
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Learned via RIP
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Convergence Issues
• Factors affecting the convergence time include
the following:
Routing protocol used
Distance of the router, or the number of hops from the
point of change
Number of routers in the network that use dynamic
routing protocols
Bandwidth and traffic load on communications links
Load on the router
Traffic patterns in relation to the topology change
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The Initiation of Routing Updates
• Routing protocols can instruct a router to update neighbors
after a specific amount of time has passed, after a certain event
has occurred, or both.
• Time-driven routing protocols wait for the update timer to expire
and then send an update.
Periodic updates
• Protocols that are event-driven do not require the router to
update neighbors until the router detects a change in the
network topology.
Triggered updates or incremental updates
• Routing protocols that are exclusively time-driven react poorly
to topology changes.
• Routing protocols that are exclusively event-driven could go for
extended periods of time without sending updates.
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Routing Metrics
• A routing metric is a value that measures distance to
a destination network.
• Some routing protocols use only one factor to
calculate a metric while others base their metric on
two or more factors, including hop count, bandwidth,
delay, load, reliability, and maximum transmission
unit (MTU) – these are called composite metrics
• The more factors that make up a metric, the greater
the ability is to adapt network operation to meet
specific needs.
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Summary
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