IPv4 Routing

Question 1

What are two types of rounting protocols?

Answer 1

Link State and Distante Vector

Question 2

What is the metric used by RIP routing protocol?

Answer 2

Hop Count

Question 3

Why RIP is a poorly designed routing protocol? Think about the metric it uses.

Answer 3

It uses only hop count as the metric but it does not take into account other factors like bandwidth or delay

Question 4

Which rounting protocol type (Link State vs Distance Vector) has higher visibility on the network? Why

Answer 4

Link State.
Routers using Link State protocols have the full visibility over the network whereas Distance Vector use so called ‘routing by rumour’ which means that they only know what they are told by the neighbouring routers but cannot verify information themselves.

Question 5

What are the advantages and disadvantages for Link State routing protocols?

Answer 5

Advantages:
- Better visibility of the network. Rounters can make better forwrding decisions

Disadvantages:

• Difficult to configure
• Require more memory and processing power

Question 6

What is Adminisrative Distance?

Answer 6

It’s an indicator of how ‘believable’ a given route/path is

Question 7

The higher the administratie distance, the better or worse it is?

Answer 7

Worse

Question 8

What are the Administratie Distance default values?

Answer 8

Connected Interface: 0
Static Route: 1
EIGRP: 90
OSPF: 110
RIP: 120
Unknown: 255

Question 9

Why classless rounting protocols are preferred over classful rounting protocols?

Answer 9

Because classless protocols advertise network masks

Question 10

What is VLSM

Answer 10

Variable Length Subnet Mask

Question 11

When is Administrative Distance used as a tie breaker?

Answer 11

When two different routing protocols advertise different routes for the same destination IP address

Question 12

If the same route is advertised twice on the same router, but with different outgoing interfaces, what will the tie breaker be?

Answer 12

Administrative distance

Question 13

There is a message that Link State routing protocols flood the network with to build their topological databases.
How are those messages calles

Answer 13

LSA (Link State Advertisement)

Question 14

List two examples of a LInk State routing protocol

Answer 14

OSPF - Open Shortest Path First

IS-IS - Intermediate System - Intermediate System

Question 15

OSPF is able to split whole AS (autonomous systems) into smaller groupings. How are those groups called?

Answer 15

Areas

Question 16

In OSPF, how do we call a router in between areas?

Answer 16

ABR (Area Border Router)

Question 17

What is an ASBR?

Answer 17

Autonomous System Border Router. It connects AS to the Internet.

Question 18

What is a rounting table?

Answer 18

List of networks that the router knows about and information how to link those networks.
Each entry contains a destination network (with subnet mask), out-going interface and the next hop router

Question 19

What happens with an entry in the routing table if its outgoing interface goes down?

Answer 19

It’s removed from the routing table

Question 20

What is a Default Route in a routing table?

Answer 20

It’s an optional route that is used when no explicit path to a destination is found

Question 21

What is a Default Gateway?

Answer 21

It’s an IP address that devices send traffic to if they don’t have the destination IP address in their routing tables

Question 22

How can you create a default route on a layer 3 device? [There’s a command for that]

Answer 22

IF ‘ip routing’ command is enabled use:
ip route 0.0.0.0 0.0.0.0 [ip address of the default gateway]
if it’s disabled, use:
ip default-gateway [ip address of the default gateway]

Question 23

Can you have multiple default gateways on one Layer 3 device?
If not. why not?
If yes, what would the consequences be?

Answer 23

Yes.
The device will load-balance traffic among all default routes if the administrative distance is the same. If not, the route with lowest administrative distance wins.

Question 24

Why would ‘show running-config’ command show 3 different routes to the same destination when ‘show ip route’ shows only 1 route to the given destination?

Answer 24

IP Routing Tables pull only the best route available with Administrative Distance being the tie breaker

Question 25

What is VSLM?

Answer 25

Variable Length Subnet Mask

Question 26

What is CIDR

Answer 26

Classless Inter Domain Routing

Question 27

What are the advantages of VLSM?

Answer 27

1. More efficient use of IP addresses
2. Fewer updates
3. Hide topology changes
4. Hierarchical levels for better route sumarization