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SEMESTER 2 Chapter 3
Introduction to Dynamic Routing Protocols
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3.1.1
3.1.1.2
What are the four routing
protocols that are the focus of
this course?
What are routing protocols?
What is one of the primary
benefits of using a dynamic
routing protocol?
Do dynamic routing protocols
require more or less
administrative overhead as
compared to static routing?
What is he expense of using
dynamic routing protocols?
3.1.2.1
A set of processes, algorithms,
and messages that are used to
exchange routing information
and populate the routing table
with the routing protocol's
choice of best paths is the
definition of what networking
process?
What are the purposes of a
routing protocol?
List and define the three
components of routing
protocols?
What are the four general
operations of a dynamic routing
protocol?
RIP, RIPv2, EIGRP, OSPFv2
allow routers to dynamically share information about
remote networks and automatically add this
information to their own routing tables
routers exchange routing information whenever
there is a topology change
Less
dedicating part of a router's resources for protocol
operation including CPU time and network link
bandwidth
Routing protocol
Discovery of remote networks
Maintaining up-to-date routing information
Choosing the best path to destination networks
Ability to find a new best path if the current path is
no longer available
Data structures - Some routing protocols use tables
and/or databases for its operations. This information
is kept in RAM,
Algorithm- An algorithm is a finite list of steps used
in accomplishing a task. Routing protocols use
algorithms for facilitating routing information and for
best path determination.
Routing protocol messages - Routing protocols use
various types of messages to discover neighboring
routers, exchange routing information, and other
tasks to learn and maintain accurate information
about the network.
The router sends and receives routing messages on
its interfaces.
The router shares routing messages and routing
information with other routers that are using the
3.1.3.1
What are the primary uses for
static routing?
What are the advantages of
static routing?
What are disadvantages of
static routing?
What are the advantages of
dynamic routing?
What are the disadvantages of
dynamic routing?
3.2.1
3.2.2
What are the distance vector
protocols?
What are the link state
protocols?
What is the exterior routing
protocol listed?
What is an Autonomous
System?
What is another name for an
Autonomous System?
What are Interior Gateway
Protocols used for?
What are Exterior Gateway
same routing protocol.
Routers exchange routing information to learn about
remote networks.
When a router detects a topology change the
routing protocol can advertise this change to other
routers.
Providing ease of routing table maintenance in
smaller networks that are not expected to grow
significantly.
Routing to and from stub networks.
Use of a single default route, used to represent a
path to any network that does not have a more
specific match with another route in the routing
table.
Minimal CPU processing.
Easier for administrator to understand.
Easy to configure.
Configuration and maintenance is time-consuming.
Configuration is error-prone, especially in large
networks.
Administrator intervention is required to maintain
changing route information.
Does not scale well with growing networks;
maintenance becomes cumbersome.
Requires complete knowledge of the whole network
for proper implementation.
Administrator has less work maintaining the
configuration when adding or deleting networks.
Protocols automatically react to the topology
changes.
Configuration is less error-prone.
More scalable, growing the network usually does
not present a problem.
Router resources are used (CPU cycles, memory
and link bandwidth).
More administrator knowledge is required for
configuration, verification, and troubleshooting.
RIPv1, RIPv2, IGRP, EIGRP
IS-IS, OSPF
BGP
a collection of routers under a common
administration
Domain
intra-autonomous system routing - routing inside an
autonomous system
inter-autonomous system routing - routing between
3.2.3
Protocols used for?
What are the two classifications
of IGP’s?
What is a vector?
Define distance and direction.
Where does a distance vector
router receive its information
from?
Do distance vector protocols
have a map of the entire
network?
Where do distance vector
protocols work best?
3.2.3.2
What can a link-state router do
that a link state router can not?
Define converged.
When are updates sent in a
link-state network?
What are the best situations to
use a link-state protocol?
3.2.4
3.2.5
What do classful routing
protocols not send in their
updates?
What is the situation where you
can not use a classful routing
protocol?
What are the two classful
routing protocols?
What do classless routing
protocols include in their
updates?
What are the classless routing
protocols?
Define convergence?
What is convergence time?
autonomous systems
Distance vector routing protocols
Link-state routing protocols
distance and direction
Distance is defined in terms of a metric such as hop
count and direction is simply the next-hop router or
exit interface
From its neighbors
No
The network is simple and flat and does not require
a special hierarchical design.
The administrators do not have enough knowledge
to configure and troubleshoot link-state protocols.
Specific types of networks, such as hub-and-spoke
networks, are being implemented.
Worst-case convergence times in a network are not
a concern.
Get a complete view of the topology of the network
When intermediate devices all have the same
consistent network topology in their routing tables.
Only when the topology changes
The network design is hierarchical, usually
occurring in large networks.
The administrators have a good knowledge of the
implemented link-state routing protocol.
Fast convergence of the network is crucial.
Subnet masks
When you use different subnet masks
RIP and IGRP
Subnet mask
RIPv2, EIGRP, OSPF, IS-IS, BGP
when all routers' routing tables are at a state of
consistency
the time it takes routers to share information,
calculate best paths, and update their routing tables
3.3.1
Which 2 protocols are slow to
converge?
Which 2 protocols are faster to
converge?
What is a metric?
What is the metric used for?
What is the metric for RIP?
What is the metric for EIGRP?
What is the metric for OSPF?
What does hop count refer to?
3.3.2
3.3.2.2
3.3.3
Can metrics from one routing
protocol be compared to
another routing protocol’s
metric?
List and define the possible
metrics to choose from?
List and explain each routing
protocol and the metric it uses.
In the show ip route display
where is the metric listed?
What is the process used to
forward packets when 2 or
more paths have equal costs?
Where can you look to
determine if load balancing is
RIP and IGRP
EIGRP and OSPF
a value used by routing protocols to assign costs to
reach remote networks
to determine which path is most preferable when
there are multiple paths to the same remote
network
Hop count
A combination of bandwidth and delay
Bandwidth
the number of routers a packet must cross to reach
the destination network
No they are not comparable
Hop count - A simple metric that counts the number
of routers a packet must traverse
Bandwidth - Influences path selection by preferring
the path with the highest bandwidth
Load - Considers the traffic utilization of a certain
link
Delay - Considers the time a packet takes to
traverse a path
Reliability - Assesses the probability of a link failure,
calculated from the interface error count or previous
link failures
Cost - A value determined either by the IOS or by
the network administrator to indicate preference for
a route. Cost can represent a metric, a combination
of metrics or a policy.
RIP: Hop count - Best path is chosen by the
route with the lowest hop count.
IGRP and EIGRP: Bandwidth, Delay, Reliability,
and Load - Best path is chosen by the route with
the smallest composite metric value calculated
from these multiple parameters. By default, only
bandwidth and delay are used.
IS-IS and OSPF: Cost - Best path is chosen by
the route with the lowest cost. . Cisco's
implementation of OSPF uses bandwidth.
The second value in the brackets.
Load balancing
The routing table and look for multiple paths to the
same destination network
being used?
What are the possible values
for Administrative Distance?
What is the best value for
administrative distance?
What type of route has the
lowest possible administrative
distance?
What does an administrative
distance of 255 mean?
Where can you find the
administrative distance in the
show ip route output?
How does a router choose the
best path if two routing
protocols are being used?
What are the two commands in
which you can determine what
the administrative distance is?
What is the administrative
distance for a static route?
If you configure a route to a
destination also learned by a
dynamic routing protocol, what
would you set the
administrative distance to?
What command can be issued
to see the AD of a specific
route?
Can you change the AD of a
directly connected route?
What command can be issued
to see the AD of a directly
connected route?
This is excellent practice for the
exam. These are easy
questions to right and if you
practice they are easy to
answer.
3.4.1
3.4.1.2
3.4.3
3.4.4
3.5.1


0 to 255
0
A directly connected network
The router will not believe the route and will not
install it in it’s routing table
The first number in the brackets
Administrative distance
Show ip route
Show ip protocols
1
Greater than that of the routing protocol
Show ip route [route]
no
Show ip route [route]
Administrative distance is an integer value that is used to indicate a router’s
“trustworthiness”
- In general, the smaller the AD, the trustworthy the routing protocol.
Metrics are used by dynamic routing protocols to calculate the best path to a
destination.
- In general, the smaller the metric, the better the path.
* Make sure you understand the principle of routing process. When a router received a
packet and it sees there are multiple routes available in the routing table, it will decide
how to route the packet based on
1) The longest bit that match between the packet and the entries in the routing
table. If not then go to the next step.
2) Check for the lowest administrative distance. If there is a lower one, it will use
it. If they are tie, then go to next step.
3) Check for the lowest metric. If there is a lower one, it will use it. If they are tie,
then go to next step.
4) Now, you have equal-cost load balancing. The next thing you need to decide
whether you have per destination or per packet load balancing. (Unequal cost
load balancing is a difference process,)
5) EIGRP can be tweaked and run unequal cost load balancing, but by default
they still using equal cost load balancing.
* The following is the example of equal cost in RIP. What is the purpose of listing 2
entries under one network statement?
* What is "routing protocol"? What is the purpose of "dynamic routing protocol"?
* What is administrative distance? How does it get used to decide the route get used in
the router?
* What is metric? How does it get used to decide the route get used in the router?
* Refer to the graphic below, when PC2 wants to access PC5, and you have multiple
ways to get to it, but there exist only one prefer route and the other route will not get
used?
- Which route is the prefer route? Why?
* You need to memorize the following properties:
 Static route: AD: ______ Metric:______
 Connected route: AD: ______ Metric:______
 RIP route: AD: ______ Metric:_____________ (name of the metric variable)
 OSPF route: AD: ______ Metric:___________ (name of the metric variable)
 EIGRP route: AD: ______ Metric:__________ (name of the metric variable)
* You need to be able to dissect and understand the “show ip route” output:
For example:
- R 220.165.201.0/24 [120/3] via 192.168.25.2, 00:00:16, S0/0/0
- What is the significant of the information R?
- What is the significant of the information 220.165.201.0?
- What is the significant of the information /24?
- What is the significant of the information 120?
- What is the significant of the information 3?
- What is the significant of the information 192.168.25.2?
- What is the significant of the information S0/0/0?
- O 10.10.1.0/27 [110/65] via 192.168.1.5, 00:00:05, Serial0/0/1
- What is the significant of the information O?
- What is the significant of the information 10.10.1.0?
- What is the significant of the information /27?
- What is the significant of the information 110?
- What is the significant of the information 65?
- What is the significant of the information 192.168.1.5?
- What is the significant of the information S0/0/1?
* What types of routing protocols are proprietary routing protocols? * What types of
routing protocols are none-proprietary routing protocols? What does proprietary
means?
* What is classful routing protocol? What is classless routing protocol?
- What is the difference between classful and classless routing protocol?
- Which type of routing protocols requires networks to have the same mask?
- Which type of routing protocols allows networks to have the different mask?
* What is load balancing? What command can you use to check whether your router
has configured to use load balancing to distribute your packets?
* What are the characteristics of "distance vector" routing protocol?
* What are the characteristics of "link state" routing protocol?
* What are the advantage and disadvantage of static routing?
* What are the advantage and disadvantage of dynamic routing?
* When consider to install a network routing protocol, under what circumstance would
you choose to use "distance vector" routing protocol" over "link state" routing protocol?
On the other hand, under what circumstance would you choose to use "link state"
routing protocol" over "distance vector" routing protocol?
 Distance vector protocols work best in situations where:
– The network is simple and flat and does not require a special hierarchical
design.
– The administrators do not have enough knowledge to configure and
troubleshoot link-state protocols.
– Specific types of networks, such as hub-and-spoke networks, are being
implemented.
– Worst-case convergence times in a network are not a concern.
 Link-state protocols work best in situations where:
– The network design is hierarchical, usually occurring in large networks.
– The administrators have a good knowledge of the implemented link-state
routing protocol.
– Fast convergence of the network is crucial.
* What does it mean by networks in the router are converged?
* Why is fast convergence a desirable characteristic of routing protocol? Can the router
forward packet before networks get converged with other router? Why? Why not? Is
there any downside of this action?
* What commands do you need to create a "Connected" route in the routing table?
Example:
 Router(config)# interface "type"
 Router(config-if)# ip address "x.x.x.x y.y.y.y"
 Router(config-if)# no shutdown
* What commands do you need to create a "static" route in the routing table?
Router(config)# ip route [Remote network + network mask] [exit interface (or) next hop IP]
* You need to be able to count the metric in RIP. Why the metric in the following
diagram is 2?