Cisco | CCNA | Router | Routing Protocols | Interview Questions

Regularly placed Routing Protocols Questions:

Hello friends, welcome back to my Networking Interview Questions Blog series. In the last blog, I covered Subnetting and Supernetting interview questions and Answers. Now, in this blog, I am going to cover the next very important topic – Router and its Routing Protocols. Particularly this is Part-I of this topic. As this is the core topic of CCNA, there is Part-II for the same.

So let’s start with basic questions based on Router and its components.

• What is a Router?

A Router is a networking device used to connect 2 or more different networks i.e. it provides WAN connectivity. IT performs routing which means it routes packets between devices that are on different networks with the best available path.

A router is a Layer 3 – Network layer device work on IP address i.e. on packets as PDU.

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• What is Routing?

The function of routing is to route packets between different networks using the best available paths to the destination network.

• What are the different types of memory in the router?

RAM – Stores current configuration file: running-config

NVRAM – Stores saved Configuration file: startup-config

Flash Memory – Stores IOS – Internetwork Operating System.

ROM – Stores instructions for POST, Bootstrap program, Mini-IOS.

• What are the possible locations of the IOS image?

FLASH – Default IOS location

TFTP Server – Network location

• What are the different modes in the router?

1. User Exec Mode – In User Exec mode, we can only view the configuration settings on the device, but all “show” commands cannot work in this mode. IOS prompt in user exec mode is

Router>

Command to navigate to next mode, Privilege mode from user exec mode: –

Router>enable

Router#

2. Privilege Mode – In Privilege mode, we can view, copy, save and erase configuration of a router. IOS prompt in Privilege Mode is

Router#

Command to navigate to Global Configuration mode from Privilege mode: –

Router# configure terminal

Router (config) #

3. Global Configuration Mode – In Global Configuration mode we can make global changes in the Router configuration. IOS prompt in Privilege Mode is

Router (config) #

4. Specific Configuration Mode – We can navigate to a number of sub prompt from global configuration, such as the interface prompts to configure the properties of a specific interface, the line prompts to configure the properties of a specific configuration line and the router mode to configure routing protocols. IOS prompt in a specific configuration mode for line prompt is

Router (config-line) #

Example:-

Router (config) # line con 0

Router (config-if) #

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• What is the ROM Monitor?

ROM Monitor is router mode which is used in troubleshooting. If the Bootstrap program isn’t able to notice an IOS image, it will act as ROM Monitor.

ROM Monitor is capable of implementing specific configuration task such as: –

1. Changing the configuration register value etc.
2. Recovering a lost password
3. Downloading IOS image using TFTP

• What is the command to restart a router?

Router# reload

• What is the command used to enter PRIVILEGE mode from USER mode?

Router> enable

• What is the command used to enter Global Configuration mode from PRIVILEGE Mode?

Router# configure terminal / (config t)

• What is the command to take a backup of IOS to TFTP server?

Router# copy flash tftp

• What is the command to display the saved configuration in NVRAM?

Router# show startup-config

• What is CDP?

CDP – Cisco Discovery Protocol is a Cisco proprietary protocol used for collecting information about both locally attached and remote cisco devices.

• What are the different types of Routing?

There are basically two types of Routing called: Static Routing and Dynamic Routing.

One more routing type is there which is known as Default routing which can be used only on Stub networks which having a single exit path.

• What is static routing?

In static routing, routes need to be configured manually on the router by a network administrator.

There is no overhead on the router CPU, but it is not feasible in large networks because maintaining it is a full-time job. Also, human error chances are more.

• What is the Default Route?

When the destination network is unknown, the default route specifies a path that the router should take. All the IP datagrams with unknown destination network address are sent to this default route.

• What is Dynamic Routing?

In Dynamic routing, available routes are learned by using a routing protocol. Routing protocols can find out about routes from another neighboring router running a similar routing protocol. Then the router examines the best route and enters it into the routing table.

Example – RIP (Routing Info Protocol), EIGRP (Enhanced Interior Gateway Routing Protocol) and OSPF (Open Shortest Path First).

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• What is the difference between Routing and Routed Protocol?

Routing Protocols learn the routes and give the most effective routes from one network to a different network. Example- RIP, OSPF, EIGRP.

A Routed Protocol carries data from one network to another network. Routed protocol carries user traffic like file transfers, net traffic, e-mails, etc.

Example- IP, IPX and AppleTalk.

• What is an Autonomous System (AS)?

An AS – Autonomous System is a group of networks under single administrative control. Every AS has assigned a globally unique 16-digits identification number called ASN-Autonomous System Number by IANA-Internet Assigned Numbers Authority.

• Difference between IGP and EGP?

An IGP – Interior Gateway Protocol refers to a routing protocol that handles routing inside a single autonomous system. Example- RIP, IGRP, EIGRP, and OSPF.

An EGP – Exterior Gateway Protocol refers to a routing protocol that handles routing between multiple Autonomous Systems (AS). Example: – Border Gateway Protocol (BGP).

• What is Administrative Distance (AD)?

An AD – Administrative Distance defines the trustworthiness of a routing protocol. Routers use AD value to select the best path when there are more than one i.e. multiple different routes to the same destination learned through different routing protocols.

An AD value ranges from 0 to 255, where 0 is the Best and 255 is the worst.

Routing Protocol            Administrative Distance Value

Directly Connected                             0

Static route                                          1

EIGRP                                                   90

OSPF                                                   110

RIP                                                       120

• What are the different types of Routing Protocols?

There are 3 types of IGP Routing Protocols based on metrics they are used as DVR, LSR, and Hybrid.

1. DVR – Distance Vector Routing Protocols use the distance or number of hops as the metric to find the paths to destinations. The Shortest path will be the best path.

Example- Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP)

2. LSR – Link-State Routing Protocols use the bandwidth of the links as the metric to calculate the cost of paths to the destination. High bandwidth shows a low cost. Lowest cost i.e. the fastest path will be the best path.

Example- Open Shortest Path First (OSPF)

3. Hybrid Routing Protocol uses Number of Hops and Bandwidth both as metric by default to find paths to the destination, hence called as Hybrid. Fast with a low latency path will be the best path.

Example- Enhanced Interior Gateway Routing Protocol (EIGRP)

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• What is Route Metrics?

Routing Protocols use comparison factors called Route Metric value to find the best path when there are multiple different paths available to the same destination.

Different routing protocols use different route metrics to compute the cost to destination.

RIP – Hop Count

OSPF – Bandwidth

EIGRP – Bandwidth, Delay, Reliability, Load, MTU.

• What is Bandwidth, Load, Delay, Reliability, and MTU?

1. Bandwidth (BW) – The Data carrying capacity of a link in Kbps.
2. Load – It is the data traffic on the path or amount of utilization of a path.
3. Delay – It is the time takes to reach the destination.
4. Reliability – It is defined using the least amount of errors or downtime.
5. MTU – Maximum transmission unit (MTU) defines the extreme size of the packet that can be transmitted through network device or over a medium.

• What are the four timers available in RIP?

Route Update timer (30 seconds) – the time interval between periodic routing updates in which the router sends a complete copy of its routing table out to all neighbor routers.

Route Invalid timer (180 seconds) – the time interval before a router determines that a route has become invalid. A route will become invalid if it has not heard any updates about a particular route for this invalid time period.

Route Hold down timer (180 seconds) – It is the amount of time during which routing information is suppressed. Routes can enter into the holddown state once a router gets an update that indicates the particular route is not reachable. This will continue either up to the router gets a new update packet with a better metric or till the holddown timer expires.

Route Flush timer (240 seconds) – It is the time between a route turn into invalid and its removal from the routing table. Before it’s removed from the table, the router notifies its neighbor routers of that invalid route.

• Which protocol and port number are used by RIP?

RIP uses User Datagram Protocol (UDP) with 520 as port number.

• Difference between RIPV1 & RIPV2?

RIPv1	RIPv2
Classful routing protocol.	Classless routing protocol.
Sends only network addresses.	Sends network address with netmask.
Uses broadcasts for updates.	Uses multicasts for updates.
It does not support VLSM.	Supports VLSM.
It does not supports authentication.	Supports authentication.

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• What is the multicast address of RIPv2?

RIPv2 uses 224.0.0.9 multicast address for sending updates.

• What is Split Horizon?

The Split Horizon feature stops the update of a route learned on one interface from being advertised back to that same interface.

• What is Route Poisoning?

Using route poisoning, when a distance vector routing protocol observes that a route is no longer valid, it is advertised with an infinite metric i.e. in RIP 16^th Hop count, indicating that the route is bad.

With this, I am concluding this blog. In this blog, you got the questions related to the Router, its components, Basic configuration, Metrics, and Routing protocol RIP. In the next part of this blog series, I will include questions-answers on OSPF and EIGRP.

Author:- Sumaiyya Suhail Bagwan
Department Name:- Networking
Designation:- Technical Trainer

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