TOP 10 CCNA CCNP Interview Questions

In this article, I shared the frequently asked CCNA CCNP interview questions. To get the best idea about the interview questions, read the job description carefully, from there you will get the right clue about the questions.  

I gave many interviews and very few questions that are common in all interviews (explain DHCP server and DNS server, explain STP, explain OSI model with each layer, difference between TCP and UDP) others questions are completely different, and after giving 3-4 interview I realized there are no standard questions for all interviews, you need to understand the profile requirement.  

For example, if you are fresher and you have completed CCNA training or CCNA certification and now you are applying for a security profile then surely more questions are related to security concepts like what is VPN, explain TCP header, or what is firewall and related stuff, Join CCNA and CCNP Certification And if you are applying for a routing and switching profile then questions are related to routing protocols, like RIP, OSPF and EIGRP and VLANs. 

How does traceroute work? 

Traceroute and ping both are very helpful in troubleshooting. Both work under ICMP protocol. Ping is used to check the connectivity. But when the destination is unreachable, we use the traceroute command to find out where the problem is or you can say to find which router is down. 

Traceroute command shows the information of all hops of a route over that packet is transmitted source to destination. When we run the traceroute command, it sends the 3 messages to each hop one by one and then each hop sends back these messages to the source with their IP address and round-trip time. 

TTL (time to live) value is decremented by 1 as the IP packet traverses the path. The TTL value is mainly used to avoid layer 3 loops. 

What is MTU? 

MTU stands for maximum transmission unit. It defines the maximum length of a packet that can be sent over the internet. MTU value is different for different protocols. For ethernet, it is 1500 bytes. Whenever packet size is larger than MTU, the packet is fragmented into smaller parts before transmission. 

What is MSS? 

MSS stands for maximum segment size. When data comes from the upper layers to the transport layer, a header portion (TCP header) is added at the transport layer, IP header is added at the network layer. This way you can see, inside the packet along with data, headers are also present. The actual size of data (payload) in bytes is called MSS. 

Inside the packet, mainly there are 3 fields- TCP header, IP header and data. 

MTU – header size (IP header and TCP header) = MSS. 

What is VPN? 

VPN stands for Virtual Private Network. VPN provides a secure and encrypted way to transmit information over the internet. The Internet is a public network, everyone can access the internet, so when we transmit data over the internet, security is our first concern to ensure secure transmission. VPN uses tunneling protocols to establish a secure and encrypted private channel. 

VPN is used to securely connect the remote location users to the private network.  

Types of VPN 

• Site to site VPN 
• Remote Access VPN 

How does HSRP work? 

HSRP stands for Hot Standby Routing Protocol. It is also known as gateway redundancy protocol. 

HSRP is used for gateway load balancing. It allows you to configure HSRP in 2 routers for a single LAN network. At one time, one router will act as an active router and another router will stay in standby mode. When an active router fails due to any technical issue, traffic automatically shifts to the standby router. 

Why do we use area concepts in OSPF? 

In a smaller network, there is no need to have multiple areas, area 0 is sufficient. But, for a larger network, a single area is not a good choice, it will impact the network performance in a bad way. 

• SPF algorithm will take more time to calculate the best route. 
• To manage large database routers, requires more processing power and more memory. 
• If changes occur in the network, LSAs (link state advertisements) are generated and every router floods the LSA to their neighbours. And after this again SPF algorithm runs to update their routes. 

So, this way you can understand, to reduce LSA flooding, to reduce CPU resources utilization, we create areas in OSPF. 

What are the conditions to design the OSPF areas? 

• Area 0 (backbone area) is mandatory. 
• All areas should be continuous. 
• All areas should be connected to the backbone area. 

Explain OSPF States? 

There are 7 states in OSPF. 

1. Down  
2. Init 
3. 2-way state 
4. Ex start 
5. Exchange 
6. Loading 
7. full 

How many LSAs are present in OSPF routing protocol? 

There are 8 LSAs. 

How does BGP select the best path? 

If there are multiple routes present for the same source to destination, then BGP uses below parameters to choose the best route. 

• Prefer the path with highest weight and local preference value. 
• Prefer the path with shortest AS_ path. 

• Prefer the path with the lowest origin type and multi-exit discriminator (MED). 
• Prefer eBGP over iBGP paths. 
• Prefer the path that comes from the router with the lowest router-ID. 
• Prefer paths with lowest cluster length value. 

Which attributes manipulate incoming traffic and which attribute manipulate outgoing traffic? 

Why do we use area concepts in OSPF? 

Explain BGP messages? 

• Open  
• Keep Alive 
• Notification 
• Update 

BGP also uses TCP 3-way handshake to establish a connection between neighbours.  All BGP messages are unicast in nature. 

Open message: After completion of TCP 3-way handshake routers send open messages to start the BGP session. In an open message router introduces itself to other routers and also sends parameter details like version, AS number, hold-time, BGP identifier and other parameters. 

Keepalive: In response to the open message routers send a keep alive message. By default, Cisco routers send a keep-alive message every 60 seconds. Keepalive message shows that the router is working fine. 

Update message: In the update message, routers exchange routes information that include unfeasible routes, withdrawn routes, path attributes and network layer reachability information. 

Notification message: To send the error detail to the neighbour router, notification message is sent. There are mainly 2 situations in which routers send notification messages. 

1. If the update message is not correctly received. 

2. If there is any error and because of that router needs to stop the session. 

In the notification message, error code, error sub-code and error data is sent. 

How many states are present in BGP? 

There are 6 states in the BGP protocol. 

• Idle  
• Connect 
• Active State 
• Open Sent 
• Open Confirm  
• Established