Dynamic Routing Protocols

Question 1

What does a routing protocol do?

Answer 1

Allows routers to share best paths to known networks with each other.

Question 2

How do routers utilize routing protocols?

Answer 2

Routers take the information of best known paths from other routers to determine their own best path. This includes when routing paths go down or when network states change. These changes are done automatically.

Question 3

What are the two types of routing protocols

Answer 3

Internal Gateway Protocols (IGPs) and External Gateway Protocols (EGPs)

Question 4

What are interior gateway protocols (IGPs) used for?

Answer 4

Exchanging routing information between routers within an organization.

Question 5

What are exterior gateway protocols (EGPs) used for?

Answer 5

Exchanging routing information over the Internet between organizations.

Question 6

What are the types of EGPs used today?

Answer 6

Path Vector Routing Protocol.

Question 7

What are the types of IGPs used today?

Answer 7

Distance Vector routing protocols and Link state routing protocols.

Question 8

How do Distance Vector routing protocols work?

Answer 8

Routers only know what’s connected to them and their neighbors.

Question 9

How do Link State routing protocols work?

Answer 9

Routers shares its connections to its neighbors and that information is passed to every other router in the network.

Question 10

What are examples of Distance Vector routing protocols?

Answer 10

Routing Information Protocol (RIP) and Enhanced Interior Gateway Routing Protocol (EIGRP)

Question 11

What are examples of Link State routing protocols?

Answer 11

Open Shortest Path First (OSPF) and Intermediate System - Intermediate System (IS-IS)

Question 12

What is an example of a Path Vector Routing Protocol

Answer 12

Border Gateway Protocol (BGP). This is the only EGP used today.

Question 13

How do IGPs know which path to put into a router’s routing table?

Answer 13

Each IGP use a different method to calculate a metric value. The lower the metric value, the better the path. This determines which path is the best path.

Question 14

How do Distance Vector metrics work?

Answer 14

Each router advertises its known network and shares their metric to get to each of them.

Question 15

How do Link State metrics work?

Answer 15

Each router takes the information of all the other routers and network information and calculates its own best path.

Question 16

How do Routing Information Protocol (RIP) Metrics work?

Answer 16

They use hop count, meaning how many routers they go through to get to a destination. Cannot really manipulate the metrics.

Question 17

How do Open Shortest Path First (OSPF) Metrics work?

Answer 17

It uses a “cost” method, where it takes into account bandwidth by default.

Question 18

How do IS-IS Metrics work?

Answer 18

Also uses a “cost” method, but does not take into account bandwidth. If costs are not manually set, it takes the lowest hop count.

Question 19

How do EIGRP Metrics work?

Answer 19

Uses a calculated number determined primarily by bandwidth. Can manually configure path if needed.

Question 20

What happens when multiple paths have the same cost in IGPs?

Answer 20

All IGPs use Equal Cost Multi Path (ECMP) by adding all paths into the routing table and load balancing the information between them.

Question 21

What is the purpose of Administrative Distance

Answer 21

Administrative distance is used to determine the priority and best path when routers use multiple routing protocols.

Question 22

How does administrative distance work?

Answer 22

Priority values are assigned to different routing protocols to determine which protocol to use and then it uses metrics to determine which path to take.

Question 23

What is the purpose of floating static routes

Answer 23

Because static routes have a value of 1, administrative distance will always take the static path route. Floating static routes allows us to assign static routes as a backup route in case the original best path fails. This is done by assigning a AD value just above the priority value of the routing protocol.

Question 24

What is a loopback interface?

Answer 24

Virtual interface that’s always up as long as there’s one IP interface that works

Question 25

If a path is down, how does a loopback interface solve this issue?

Answer 25

A loopback interface allows a single address across multiple interfaces so that when on path goes down, traffic can be rerouted to another interface.

Question 26

What is the purpose of a passive interface

Answer 26

Passive interfaces allows you to know about the link, while not sending routing information to the device on the other side. Think of it like one way streets.

Question 27

Why should you always configure a loopback interface as a passive interface.

Answer 27

This way it will advertise its information, but not waste resources sending out and listening for hello packets. Loopbacks will never have adjacencies.