Hello Guys, myself Bipul Roy, I am dual CCIE (CCIE#36690). I have worked long 12 years in the IP networking industry with different companies. So, I have prepared this list of interview questions based on my working experience and networking knowledge. These are the very common questions asked by the interviewer from the Device Management and Basic Routing sections. I hope this will help you to prepare the networking interview. Best of luck and Thank you.
1. What is the router?
The router is a Layer 3 of the OSI model device. It does packet forwarding based on the IP routing table.
2. What is Routing?
Routing means packet forwarding between different networks/subnet. Routing is the process of receiving an IP packet, making a decision of where to send the packet next, and then forwarding the packet.
3. What is the IP routing table?
The router maintains a table called IP routing table, that consists of all the learned IP networks or routes (local and remote) either directly connected or statically or dynamically.
4. Which command is used to show the routing table?
“Router#show IP route” command is used to see the routing table of a router.
5. What is Packet Re-write?
When a router decides to forward a packet, it does process the received packet, actually de-encapsulating the packet header information, this is called packet re-write.
6. What are the Routing and Routed protocols?
The routing protocol will choose the best path. For example; RIP, EIGRP, OSPF, etc.
Routed Protocol will carry the data over the best path. For Example; IP.
7. What is a dynamic routing protocol?
The Routing protocol which builds the Routing table dynamically by sending or receiving Routing update.
8. What are IGP and EGP?
Interior Gateway Protocols (IGP): Used for routing within an AS (Autonomous System). It is also referred to as intra-AS routing. Ex: RIPv1, RIPv2, OSPF, EIGRP, IS-IS.
Exterior Gateway Protocols (EGP): Used for routing between autonomous systems. It is also referred to as inter-AS routing. Ex: BGP.
9. What is Distance Vector routing?
Distance Vector routing means, Distance specifies how far (distance) it is to reach the destination network and Vector means direction, which specifies the next-hop router or exit interface to reach the destination. Ex: RIPv1, RIPv2, IGRP, and EIGRP.
10. What is Link State Routing protocol?
A link-state routing protocol is that which uses the link-state (Link statistics, which means Interface IP, subnet mask, metric) information to create a topology map. Ex: OSPF, IS-IS.
11. What is the difference between Link State and Distance Vector?
The entire routing table is sent as an update.
Updates are periodic.
Routers don’t have an entire topology view.
Slow convergence time.
An entire routing table is not sent as an update.
Updates are not periodic, only sent when there is a change.
Routers have an entire topology view.
Fast convergence time.
12. What is the Path Vector routing protocol?
Path vector routing includes path information along the routes with direction. BGP is a Path Vector routing protocol.
13. What is a Classful and Classless routing protocol?
A Classful routing protocol does automatic summarization at the classful network boundary. Ex: RIPv1, EIGRP.
Classless Routing Protocol does not summarize automatically at the classful network boundary. Ex: RIPv2, EIGRP, OSPF, IS-IS.
14. What is Metric?
Metric is used by Dynamic Routing Protocol. It is a mathematically calculated value to select the best path when a routing protocol learns more than one route to the same destination.
15. What is AD?
The Administrative Distance (AD) is a measure of trustworthiness of the routing information received.
16. What is the difference between the Router and Switch?
The major difference between Cisco Switch and Router is that Router does packet forwarding based on the IP Routing table and Switch does Frame forwarding based on the MAC table. A switch works at the Datalink layer and Router works at Network Layer. A switch is a Lan Device, Router is a WAN device.
17. Why does the router maintain the ARP table?
This ARP table is useful when the router has to re-encapsulate the received packet.
18. What is IOS?
The operating system of Cisco Switch and Router is known as IOS (Internetwork Operating System).
19. What is a Console port?
The console port is a physical interface/port use to manage the device locally.
20. What is Rollover cable?
Rollover cable also is known as Console cable used to connect Router or Switch with a PC/Laptop for management purposes.
21. What are the different memory components of the Router and Switch?
RAM, Flash, ROM, NVRAM.
22. What is the purpose of Flash memory?
Flash memory stores IOS.
23. What is the purpose of NVRAM?
NVRAM is a non-volatile RAM, stores startup configuration or saved configuration.
24. What is the purpose of RAM?
RAM is volatile in nature handles all current operations.
25. What is the command to see a running configuration?
26. What is the command to see startup configuration?
27. What are the modes available on IOS?
IOS Native Mode: this is the normal mode of CISCO IOS.
Setup mode: When only the default configuration is present in a device (router/switch), it will ask to enter a mode called setup mode.
ROMMON mode: ROM Monitor mode, low-level diagnostic mode. If IOS is corrupted or forgot password, this mode is used.
28. What is the difference between ‘enable secret’ and ‘enable password’ command?
‘Enable secret’ command sets a more secure password than ‘enable password’ command, as the first one uses an MD5 hashing algorithm to encrypt the password in IOS.
29. Describe the IOS boot sequence?
- The router performs a POST (Power on Self-Test) to check all hardware components.
- The router copies a bootstrap program from ROM into RAM and starts.
- The bootstrap program decides which IOS image to load from flash and load the IOS image file.
- Once the IOS image is loaded on the router, it finds the startup configuration in NVRAM. If it finds Startup configuration then it loads it into RAM and makes the device operational.
30. What is the configuration register?
Configuration register is 16 bit, use a hexadecimal value that defines how router boots and finds IOS and configuration files. The default value of the Configuration Register is set to 0x2102 which means the device will find the IOS image file in Flash memory, also it will find the configuration file in NVRAM to boot in normal mode.
31. What is the purpose of the ‘show version’ command?
‘Show version’ command output shows may things; IOS version, device uptime, device serial number, device components, device model, etc.
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