SEMESTER 2 Chapter 3
Introduction to Dynamic Routing Protocols
V 4.0
3.1.1 / What are the four routing protocols that are the focus of this course? / RIP, RIPv2, EIGRP, OSPFv23.1.1.2 / What are routing protocols? / allow routers to dynamically share information about remote networks and automatically add this information to their own routing tables
What is one of the primary benefits of using a dynamic routing protocol? / routers exchange routing information whenever there is a topology change
Do dynamic routing protocols require more or less administrative overhead as compared to static routing? / Less
What is he expense of using dynamic routing protocols? / dedicating part of a router's resources for protocol operation including CPU time and network link bandwidth
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? / Routing protocol
What are the purposes of a 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
List and define the three components of routing protocols? / 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.
What are the four general operations of a dynamic routing protocol? / 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 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.
3.1.3.1 / What are the primary uses for static routing? / 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.
What are the advantages of static routing? / Minimal CPU processing.
Easier for administrator to understand.
Easy to configure.
What are disadvantages of static routing? / 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.
What are the advantages of dynamic routing? / 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.
What are the disadvantages of dynamic routing? / Router resources are used (CPU cycles, memory and link bandwidth).
More administrator knowledge is required for configuration, verification, and troubleshooting.
3.2.1 / What are the distance vector protocols? / RIPv1, RIPv2, IGRP, EIGRP
What are the link state protocols? / IS-IS, OSPF
What is the exterior routing protocol listed? / BGP
3.2.2 / What is an Autonomous System? / a collection of routers under a common administration
What is another name for an Autonomous System? / Domain
What are Interior Gateway Protocols used for? / intra-autonomous system routing - routing inside an autonomous system
What are Exterior Gateway Protocols used for? / inter-autonomous system routing - routing between autonomous systems
3.2.3 / What are the two classifications of IGP’s? / Distance vector routing protocols
Link-state routing protocols
What is a vector? / distance and direction
Define 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
Where does a distance vector router receive its information from? / From its neighbors
Do distance vector protocols have a map of the entire network? / No
Where do distance vector protocols work best? / 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.
3.2.3.2 / What can a link-state router do that a link state router can not? / Get a complete view of the topology of the network
Define converged. / When intermediate devices all have the same consistent network topology in their routing tables.
When are updates sent in a link-state network? / Only when the topology changes
What are the best situations to use a link-state protocol? / 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.
3.2.4 / What do classful routing protocols not send in their updates? / Subnet masks
What is the situation where you can not use a classful routing protocol? / When you use different subnet masks
What are the two classful routing protocols? / RIP and IGRP
What do classless routing protocols include in their updates? / Subnet mask
What are the classless routing protocols? / RIPv2, EIGRP, OSPF, IS-IS, BGP
3.2.5 / Define convergence? / when all routers' routing tables are at a state of consistency
What is convergence time? / the time it takes routers to share information, calculate best paths, and update their routing tables
Which 2 protocols are slow to converge? / RIP and IGRP
Which 2 protocols are faster to converge? / EIGRP and OSPF
3.3.1 / What is a metric? / a value used by routing protocols to assign costs to reach remote networks
What is the metric used for? / to determine which path is most preferable when there are multiple paths to the same remote network
What is the metric for RIP? / Hop count
What is the metric for EIGRP? / A combination of bandwidth and delay
What is the metric for OSPF? / Bandwidth
What does hop count refer to? / the number of routers a packet must cross to reach the destination network
3.3.2 / Can metrics from one routing protocol be compared to another routing protocol’s metric? / No they are not comparable
List and define the possible metrics to choose from? / 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.
3.3.2.2 / List and explain each routing protocol and the metric it uses. / 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.
In the show ip route display where is the metric listed? / The second value in the brackets.
3.3.3 / What is the process used to forward packets when 2 or more paths have equal costs? / Load balancing
Where can you look to determine if load balancing is being used? / The routing table and look for multiple paths to the same destination network
3.4.1 / What are the possible values for Administrative Distance? / 0 to 255
What is the best value for administrative distance? / 0
What type of route has the lowest possible administrative distance? / A directly connected network
What does an administrative distance of 255 mean? / The router will not believe the route and will not install it in it’s routing table
3.4.1.2 / Where can you find the administrative distance in the show ip route output? / The first number in the brackets
How does a router choose the best path if two routing protocols are being used? / Administrative distance
What are the two commands in which you can determine what the administrative distance is? / Show ip route
Show ip protocols
3.4.3 / What is the administrative distance for a static route? / 1
If you configure a route to a destination also learned by a dynamic routing protocol, what would you set the administrative distance to? / Greater than that of the routing protocol
What command can be issued to see the AD of a specific route? / Show ip route [route]
3.4.4 / Can you change the AD of a directly connected route? / no
What command can be issued to see the AD of a directly connected route? / Show ip route [route]
3.5.1 / This is excellent practice for the exam. These are easy questions to right and if you practice they are easy to answer.
- 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 memorizethe following properties:
- Static route: AD: ______Metric:______
- Connectedroute: AD: ______Metric:______
- RIProute: AD: ______Metric:______(name of the metric variable)
- OSPFroute: AD: ______Metric:______(name of the metric variable)
- EIGRProute: 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" routingprotocol" over "link state" routing protocol? On the other hand, under what circumstance would you choose to use "link state" routingprotocol" 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?