Post on 30-May-2018
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CCNA Semester2
Module 6
Routing and Routing Protocols
Objectives
Introduction to static routing
Dynamic routing overview
Routing protocols overview
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Introduction to Static Routing
Introducing routing
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.
In order to make the correct decisions, routers
must learn the direction to remote networks.
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Route Types
The Administrative Distance
AD is a rating of the trustworthiness of a
routing information source, expressed as a
numeric value from 0 to 255. The higher the
number, the lower the trustworthiness
rating.
Example: Directed connection 0 Static route (by default) 1
IGRP 100
OSPF 110
RIP 120
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Static route
Advantages:
Require very little maintenance on small networks
No network overhead May hide parts of networks
Disadvantages:
Require a tremendous amount of administrative time on
large networks
Lack scalability
The IP ROUTE command
ip route network [ mask] { address | interface } [ distance ][ permanent ]
ip route network [ mask ] { address | interface } [ distance ][ permanent ]
Router (config)#
Defines a path to an IP destination network or subnet
ip route command Description
network destination network
mask dest. network mask
address IP address of next hop
permanent if set, route will not be removed when intf. is
shutdown
interface Name of interface to get to destination
distance Administrative distance
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Static route command
AD in static route
A route with a lower AD will be installed before
an identical route with a higher AD.
The default AD when using next-hop address is
1, while the default AD when using the outgoing
interface is 0.
If an administrative distance other than thedefault is desired, a value between 0 and 255 is
entered
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Route in Routing Table
If the router cannot reach the outgoing interfacethat is being used in the route, the route will notbe installed in the routing table.
This means if that interface is down, the routewill not be placed in the routing table
To hold the route in routing table even ifassociated outgoing interface is down, usepermenent parameter.
Default Route
Default routes are used to route packets with
destinations that do not match any of the other
routes in the routing table.
Routers are typically configured with a default
route forInternet-bound traffic.
ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing
interface]
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Using the DEFAULT IP ROUTE command
Verifying static route configuration
show running-config to verify that the static route
was entered correctly.
show ip route command to make sure that the
static route is present in the routing table.
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Troubleshooting static route configuration
Show ip route command
Ping command
Traceroute command
Dynamic Routing Overview
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Routed Protocol
A routed protocol is used to direct user traffic.
A routed protocol provides enough information
in its network layer address to allow a packet tobe forwarded from one host to another based onthe addressing scheme.
Examples of routed protocols are: Internet Protocol (IP)
Internetwork Packet Exchange (IPX)
Routing Protocol
A routing protocol is the communication used betweenrouters.
A routing protocol allows one router to shareinformation with other routers regarding the networks itknows about.
Examples of routing protocols are: Routing Information Protocol (RIP)
Interior Gateway Routing Protocol (IGRP) Enhanced Interior Gateway Routing Protocol (EIGRP)
Open Shortest Path First (OSPF)
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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 administratorassigns an identifying number to eachAS.
This autonomous system number is a 16 bit number.
Purpose of a routing protocol
The goal of a routing protocol is to build and
maintain the routing table.
This table contains the learned networks and
associated ports for those networks.
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Updating route
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 network knowledgebase needs to reflect an
accurate consistent view of the current topology.
Convergence
When all routers in an internetwork are operating with
the same routing knowledge, the internetwork is said to
have converged.
During convergence, problems may occur like: routing
loops, inconsistent traffic forwarding, inconsistent
routing table entries.
Fast convergence is desirable because it reduces theperiod of time in which routers would continue to make
incorrect routing decisions.
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Classes of routing protocols
Most routing algorithms can be classified into one oftwo categories:
distance vector
link-state
Distance vector algorithm
Pass periodic routing update (copies of arouting table) from router to router.
These regular updates between routerscommunicate topology changes.
Each router receives a routing table from its
directly connected neighbors. Distance-vector algorithms do not allow a
router to know the exact topology of aninternetwork.
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Distance Vector Discovery
Link-State Routing
Also known as Dijkstras algorithm or as SPF
(shortest path first) algorithms.
Link-state routing algorithms maintain a
complex database of topology information
A link-state routing algorithm maintains full
knowledge of distant routers and how theyinterconnect.
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Link-State Concepts
Link-State Concerns
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Distance Vector vs. Link State
Routing Protocols Overview
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Router Functions
A router has two basic functions: Path determination occurs at the network layer, enables a
router to evaluate the paths to a destination
Switching function is the internal process used by a routerto accept a packet on one interface and forward it to asecond interface on the same router.
Communicate Path Information
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Addressing: Network and Host
Network address: Used to determine path to a network
Host address: Specifies specific port or device on a network
How distances are determined
Primary objective of routing protocol is todetermine the best route to put in therouting table.
Each routing algorithm interprets what isbest in its own way.
Routing algorithm generates a number,called the metric value, for each paththrough the network.
Typically, the smaller the metric number, thebetter the path.
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Distance in Metrics
The router and network Commands
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IP Routing Configuration Tasks
Routing protocols
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Routing Information Protocol (RIP)
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.
Interior Gateway Routing Protocol (IGRP)
Cisco proprietary protocol
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.
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Open Shortest Path First (OSPF)
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.
Enhanced-IGRP (EIGRP)
Cisco proprietary protocol
It is an enhanced distance vector routing protocol.
Uses load balancing.
Uses a combination of distance vector and link-state
features.
Uses Diffused Update Algorithm (DUAL) to calculate theshortest path.
Routing updates are broadcast every 90 seconds or as
triggered by topology changes.
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Border Gateway Protocol (BGP)
Exterior routing protocol.
It is a distance vector exterior routing protocol.
Used between ISPs or ISPs and clients.
Used to route Internet traffic between
autonomous systems.
Summary
Configure static route, default route, float staticroute
Protocol administrative distance
Routed and routing protocol
Distance vector and link state routing protocol
Router functions Routing protocols metrics
IP routing configuration tasks
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Lab Topology
Lab_A
Lab_B
Lab_C
S0/1
S0/1
S0/0
F0/0
S0/1
F0/0
Lab_D
Lab_E
Lab_F
S0/0
S0/1
S0/0
F0/0
S0/1
F0/0
F0/0 F0/0
S0/1S0/0
Port Lab_A Lab_B Lab_C Lab_D Lab_E Lab_F
S0/0 N/A 199.6.13.1/24 204.204.7.1/24 142.18.0.1/16
204.204.7.2/24
192.168.1.1/24
34.10.120.1/16 N/A
S0/1 201.10.11.1/24 201.10.11.2/24 199.6.13.2/24 142.18.0.2/16 34.10.210.5/16
F0/0 172.16.11.1/24 10.0.0.1/8 172.16.11.2/24 10.0.0.2/8 192.168.1.2/24
CCNA2 Module6