Download Frank Mann CCAI-CCNA Module 6: Routing and Routing

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Module 6: Routing and Routing
Protocols
Frank Mann CCAICCNA
2
6.1 Introduction to Static Routing
Students completing this module should be able to:
Explain the significance of static routing
Configure static and default routes
Verify and troubleshoot static and default routes
Identify the classes of routing protocols
Identify distance vector routing protocols
Identify link-state routing protocols
Describe the basic characteristics of common routing
protocols
Identify interior gateway protocols
Identify exterior gateway protocols
Enable Routing Information Protocol (RIP) on a router
6.1.1 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.
• When routers use dynamic
routing, this information is
learned from other routers.
• When static routing is used,
a network administrator
configures information about
remote networks manually.
6.1.2 Static route operation
Static route operations can be divided into
these three parts:
• Network administrator configures the route
• Router installs the route in the routing table
• Packets are routed using the static route
The administrator could enter either of two
commands to accomplish this objective.
• Specify the outgoing interface.
• Specify the next-hop IP address of the
adjacent router.
6.1.2 Static route operation
Use a local interface as the gateway
Using the next hop
6.1.4 Configuring default route
forwarding
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 for Internet-bound traffic,
since it is often impractical and
unnecessary to maintain routes to all
networks in the Internet.
6.1.4 Configuring default route
forwarding
Identify another place that needs
a default route configured!
6.1.4 Configuring default route
forwarding
A default route on both Sterling and
Waycross will provide routing for all
packets that are destined for non-directly
connected networks
6.1.5 Verifying static route
configuration
After static routes are configured it is
important to verify that they are present in
the routing table and that routing is
working as expected.
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.
6.1.6 Troubleshooting static route
configuration
6.1.6 Troubleshooting static route
using Ping and Traceroute
6.2 Dynamic Routing Overview
Frank Mann CCAICCNA
15
6.2.1 Introduction to routing protocols
A routing protocol is the
communication used between
routers.
A routing protocol allows one router
to share information with other
routers regarding the networks it
knows about as well as its
proximity to other routers.
The information a router gets from
another router, using a routing
protocol, is used to build and
maintain a routing table.
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)
6.2.1 Routed versus Routing protocols
6.2.2 Autonomous systems
An autonomous system (AS) is a collection
of networks under a common
administration sharing a common routing
strategy.
To the outside world, an AS is viewed as a
single entity.
6.2.2 American Registry of Internet Numbers
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
6.2.3 Purpose of a routing protocol
and autonomous systems
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
6.2.4 Identifying the classes of routing
protocols
Most routing algorithms can be classified
into one of two categories:
• distance vector
• link-state
The distance vector routing approach
determines the direction (vector) and
distance to any link in the internetwork.
The link-state approach, also called shortest
path first (SPF), recreates the exact
topology of the entire internetwork
6.2.4 Identifying the classes of routing
protocols
6.2.5 Distance vector routing protocol
features
Distance vector routing
algorithms pass
periodic copies of a
routing table from
router to router.
These regular updates
between routers
communicate
topology changes.
Distance vector based
routing algorithms are
also known as
Bellman-Ford
algorithms.
Periodic updates to Neighboring routers
Routing updates occur when topology
changes
Distance vector algorithms call for each
router to send its entire routing table to
each of its adjacent neighbors.
Routing metrics
The routing tables include information about the
total path cost as defined by its metric and the
logical address of the first router on the path to
each network contained in the table.
6.2.6 Link-state routing protocol
features
The second basic algorithm used for routing is the
link-state algorithm. Link-state algorithms are
also known as Dijkstras algorithm or as SPF
(shortest path first) algorithms.
Link-state routing algorithms maintain a complex
database of topology information.
• The distance vector algorithm has nonspecific
information about distant networks and no knowledge
of distant routers.
• A link-state routing algorithm maintains full knowledge
of distant routers and how they interconnect.
Link State Concepts
Link State Routing Process
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.
Link State Routing Process
Link State Update process
Link State Update process
6.3 Routing Protocols Overview
A router determines the path of a packet from one
data link to another, using two basic functions:
• A path determination function
• A switching function
6.3 Routing Protocols Overview
A router determines the path of a packet from one
data link to another, using two basic functions:
• A path determination function
• A switching function
Path determination
Path determination occurs at
the network layer based on
the IP Address of the
destination.
The path determination
function enables a router to
evaluate the paths to a
destination and to establish
the preferred handling of a
packet.
The router uses the routing
table to determine the best
path and proceeds to
forward the packet using the
switching function
6.3.1 Path determination
6.3.2 Routing configuration
Enabling an IP routing
protocol on a router involves
the setting of both global
and routing parameters.
• Global tasks include
selecting a routing protocol,
such as RIP, IGRP, EIGRP or
OSPF.
• The major task in the routing
configuration mode is to
indicate IP network numbers.
Dynamic routing uses
broadcasts and multicasts
to communicate with other
routers.
Routing Configuration
6.3.3 Routing protocols
Routing protocols
At the Internet layer of the TCP/IP suite of
protocols, a router can use an IP routing protocol
to accomplish routing through the implementation
of a specific routing algorithm. 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
Routing Information Protocol
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.
Interior Gateway Routing Protocol
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.
Open Shortest Path First
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.
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 link-state
features.
• Uses Diffused Update Algorithm (DUAL) to calculate the
shortest path.
• Routing updates are broadcast every 90 seconds or as
triggered by topology changes.
Border Gateway Protocol
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
Interior vs. Exterior
Administrative Distance:
Ranking Routes
6.3.4 Autonomous systems and IGP
versus EGP
An exterior routing protocol must isolate
autonomous systems.
• Remember, autonomous systems are managed by
different administrations. Networks must have a
protocol to communicate between these different
systems.
Autonomous systems have an identifying number,
which is assigned to it by the American Registry
of Internet Numbers (ARIN) or a provider.
• This autonomous system number is a 16-bit number.
Routing protocols such as Cisco’s IGRP and EIGRP
require that a unique, autonomous system number be
assigned
6.3.5 Distance vector summary
Distance vector algorithms (also known as Bellman-Ford
algorithms) call for each router to send all or some portion
of its routing table only to its neighbors.
Distance vector algorithms perform routing decisions based
upon information provided by neighboring routers.
Distance vector protocols use fewer system resources but can
suffer from slow convergence and may use metrics that do
not scale well to larger systems.
Distance vector protocols are based on finding the distance
(number of hops) and vector (direction) to any link on the
internetwork. The algorithms involve passing copies of a
complete routing table from router to router on a periodic
basis.
6.3.6 Link-state
Link-state algorithms (also known as shortest path first
algorithms) flood routing information to all routers in the
internetwork that creates a map of the entire network.
Each router sends packets to all its neighbors. These packets
contain descriptions of the network or networks to which the
router is linked.
The routers assemble all the information into a complete view of
the internetwork topology to calculate the shortest path to all
known sites on the network. It then generates routing tables
showing the best path for any destination on the network.
Once converged, link state protocols use small update packets,
which contain only changes rather than copies of the entire
routing table.
Update packets are passed across the network in event-triggered
updates, so convergence is fast.
Labs Module 6: Routing and Routing
Protocols
Lab:
6.1.6 Configuring Static Routes
e-Lab:
6.1.2a Static Route Operation
6.1.2b Static Routes
6.1.3 Configuring Static Routes
6.1.4 Configuring Default Route Forwarding
6.1.5 Verifying Static Route configuration
6.1.6 Static Routes
6.3.2 Routing Configuration