CCNP Interview Questions

1. What are type-1 and type-2 LSAs in OSPF?

Ans: 

• Type-1 LSAs are router LSAs that each router generates for the area to which it belongs.
• Type-2 LSAs, often known as network LSAs, are generated by the DR and BDR.

2. What's the difference between a narrow and a wide IS-IS metric?

Ans: The interface metric in a narrow metric is 6 bits long, and the path metric is 10 bits long. The interface metric of a wide metric is 24 bits long, while the path metric is 32 bits long.

3. What are the three classes of routing protocols?

Ans:

• Distance vector.
• Link-state.
• Balanced hybrid.

4. What are the six different types of OSPF routes?

Ans:

• Intra-Area (O)
• Inter-Area (O IA)
• External Type 1 (E1)
• NSSA Type 1 (N1)
• External Type 2 (E2)
• NSSA Type 2 (N2)

5. Describe how an NSAP address is structured and formatted.

Ans:

An NSAP address is made up of three parts and has a length of 8 to 20 bytes:

• One to 13-byte area ID
• Six-byte system ID
• One byte NSAP selector that is always equal to zero for a router.

6. What exactly is the distinction between STP and RSTP?

Ans: STP is used to prevent switching loops in switching networks, whereas RSTP is nearly identical to STP with the exception that port forwarding timing has been reduced to zero.

7. What is IGRP (Interior Gateway Routing Protocol)?

Ans: IGRP is a distance-vector routing protocol developed by Cisco. The default hop count in IGRP is 100, and the maximum hop count is 255. IGRP's default metrics are bandwidth and line latency, but it can optionally use reliability, load, and MTU.

8. What are the four types of BGP attributes in general?

Ans:  The four general types of BGP attributes are as follows:

• Well-known mandatory.
• Well-known discretionary.
• Optional transitive.
• Optional nontransitive.

9. List all of the methods for adding a prefix to the BGP routing table.

Ans:

• Transferring a router from an IP routing table to a BGP routing table using the network command.
• Routes from the IP routing table to the BGP routing table are re-distributed.
• Learned from a BGP neighbor.

10. What is a core network?

Ans: The entire primary network resides in a core network. The entire network cannot function without a core network. The core network is connected to all routers and switches.

CCNP Intermediate Interview Questions

11. What is the function of Anycast RP?

Ans: The same IP address is assigned to two or more RPs. A unicast IP routing protocol is used to broadcast the RPs' IP addresses. Each multicast router selects the RP that is nearest to it. When an RP fails, the routers will switch to the next nearest RP after the unicast IP routing protocol converges. The MSDP is used to exchange active multicast source information between RPs.

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12. Describe four key differences between IBGP and EBG operations.

Ans:

• IBGP is a router-to-router protocol that is utilized within a single autonomous system. The EBGP protocol is used by routers in different autonomous systems to communicate with one another.
• IBGP routers must be synchronized before being sent to the IP routing database. (Unless you disable synchronization).
• The IP address of the interface used to connect with the EBGP peer is set as the next-hop attribute by EBGP. If a prefix was learned via an EBGP neighbor, the next-hop attribute is not changed when an IBGP router advertises it to an IBGP peer.
• All prefixes learned from an EBGP neighbor are advertised to all other EBGP neighbors through EBGP. Prefixes learned from one IBGP neighbor are not advertised to another IBGP neighbor by IBGP routers.

13. How does OSPF determine an interarea shortest path?

Ans: 

• First, determine the shortest route to an ABR.
• Second, determine the shortest path from area 0 to an ABR connected to the destination area.
• Third, from the ABR to the destination network, determine the shortest path across the destination area.

14. Describe how an NSAP address is structured and formatted.

Ans: An NSAP address is made up of three components, each of which is 8 to 20 bytes long.

• Area IDs range from one to 13 bytes.
• Six-byte system ID.
• One byte NSAP selector that is always equal to zero for a router.

15. Which route will be preferred if a router learns about the same network prefix through RIP, IGRP, EIGRP, and OSPF?

Ans: 

EIGRP has an administrative distance of 90.

IGRP has an administrative distance of 100.

OSPF has an administrative distance of 110.

RIP has an administrative distance of 120.

Hence, the EIGRP route is preferred.

16. Convert 12345670 8 to hexadecimal.

Ans: Convert each octal digit into three binary digits, and then convert the binary result to hexadecimal.

001 010 011 100 101 110 111 000

0010 1001 1100 1011 1011 1000

29CBB8

17. Explain the difference between reported and feasible distances, and also how they are used to calculate successors and feasible successors.

Ans: The feasible distance on the reporting router is the reported distance to a route that is sent to another router. The metric between the receiving and reporting routers is added to the reported distance to get the feasible distance. The successor is the route having the shortest possible distance. Feasible successors are routes having a reported distance less than the feasible distance.

18. Explain why postal and phone numbers can be routable.

Ans: State, city, and street are the three components of a postal address that can be used to deliver mail. The area code and exchange of a phone number are both essential. Only the state or city and state information can be used to deliver mail to the next post office at the core layer. The area code is used to deliver a phone number at the core layer.

19. Distinguish between a classful and a classless routing protocol.

Ans: Along with the network prefixes, classless routing protocols advertise the subnet mask. Classful routing protocols do not. As a reason, all subnets for the primary network number must be the same length for a classful protocol to work. Discontiguous network prefixes are also not supported by the classful protocol.

20. Why are Cisco's multicast routing protocols called protocol-independent?

Ans: The entries in the unicast IP routing table are used to make multicast forwarding decisions. You can use any dynamic interior routing system, static routes, or a combination of the two for multicast; it doesn't matter how the unicast IP routing table was formed.

CCNP Advanced Interview Questions

21. What is IP address 227.128.64.12's multicast Ethernet address?

Ans: 01 00 5E 00 00 00 is the standard Ethernet multicast address. The IP multicast address's first byte is not used. Subtract 128 from the value of the second byte if it is more than 127, resulting in a value of 0. After converting to hex, the third and fourth bytes of the IP address are used as-is. Their hexadecimal values are 40 and 0C. So, for IP multicast address 227.128.64.12, the Ethernet multicast address is 01 00 5E 00 40 0C.

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22. Determine at least four IP multicast groups that have the multicast Ethernet address of 01 00 5E 00 40 0C?

Ans: The multicast Ethernet address is determined by the IP address's low-order 32 bits. The first four bits are always 1 1 1 0, whereas the next five bits could be anything. As a consequence, the IP multicast addresses that correspond to the 01 00 5E 00 40 0C multicast Ethernet address are

1110 0000 0000 0000 0100 0000 1100 = 224.0.64.12

1110 0000 1000 0000 0100 0000 1100 = 224.128.64.12

1110 0001 0000 0000 0100 0000 1100 = 225.0.64.12

23. What Is The Difference Between Default Route Types In Is-is And Ospf Areas?

Ans: All routes are advertised into all OSPF areas by default. This comprises OSPF inter-area routes and also external routes inserted into OSPF. IS-IS injects a default route into an area instead of advertising inter-area or external routes.

24. In the context of route summarization, what does the word "information hiding" mean?

Ans: Only the state or city/state information is required at the core layer of the postal system to make a routing decision. The precise street names and numbers are masked because the core layer does not require them.

The area code is used to determine a routing decision at the telephone system's core layer. The core layer does not require or hide the specific exchange or last four digits of the phone number.

25. Why Is Bgp A Better Internet Routing Option than Igps?

Ans:
RIP version 1 and IGRP are classful protocols that do not broadcast the subnet mask.

The network diameter of RIP version 2 is restricted to 15 hops. For determining the shortest path, EIGRP, OSPF, and IS-IS use computationally intensive algorithms. For best path selection and loop identification, BGP uses basic approaches, and it can manage the large number of network prefixes required for Internet routing.

26. On a Cisco Router, how do you enable Igrp?

Ans:
On a Cisco router, enabling IGRP is similar to enabling RIP, except that you select IGRP as the protocol and add an autonomous system number.

For example: RouterA(config)#router igrp 10 (10 is the AS number)

RouterA(config-router)#network 192.168.0.0

RouterA(config-router)#network 192.168.1.0

RouterA(config-router)#network 192.168.2.0

27. Explain the distinction between unicast and multicast IP packet forwarding.

Ans: The destination IP address determines how Unicast IP packets are forwarded. The source IP address determines how multicast packets are forwarded. The multicast packet is sent to multicast neighbors if it is received on the interface used to deliver a unicast packet back to the source. The multicast packet is deleted if it is received on an interface that would not be utilized to deliver a unicast IP packet back to the source.

28. Explain how the address information is used to route mail from New York City to San Diego.

Ans: Unless the letter needs to be returned to its sender, the source address is not used. The access level post office in New York looks at the state, city, and street information to see if it is directly connected to the destination using the destination address. If this is not the case, the letter will be forwarded through a default route to the distribution layer post office. The state, city, and street information are also examined by the distribution layer post office to see if it is directly connected to an access layer post office that services the particular street. If it isn't, a default route is used to route the letter to the core level. The state name is checked at the core level post office, and if it does not equal New York, the letter is delivered to the California core post office. The letter is delivered from the California central post office to the San Diego distribution post office. The letter is delivered to the access post office that handles the destination street by the San Diego distribution post office. Finally, the access level switch routes the letter to its intended recipient.

29. Can you think of another system that uses a hierarchical delivery system to route traffic?

Ans: The system of airports. Major hub airports such as Denver, Chicago, New York, and Atlanta are found at the core routing level. People and cargo are routed through the primary airports to significant geographic areas.
Regional airports service a localized area and connect with core airports; regional airports are at the distribution layer. Finally, you can take the bus, a taxi, a train, or rent a car to get to your final destination. This is referred to as the access layer.

30. What is the meaning of the Eigrp Stuck In Active Message?