CCNA Short Interview Questions and Answers

      1. What is MTU?
                MTU stands for maximum transmission unit. This is the largest PDU (protocol data unit) that the layer can pass on. There are certain standards within a protocol which make it so that the MTU can be manipulated. Not all protocols however allow the MTU to be edited.

2. What is a VPN?

                Virtual private networks are logical networks created between pieces of equipment. The most common instance of this is when a user is at home and needs to connect to their business’ network in order to access the business’ resources.

3. What is a VLAN?

                VLAN stands for Virtual Local Area Network. Local area networks are typically housed on 1 switch. This allows a group of hosts to think that they are on the same broadcast domain even though they may or may not be in the same physical area. SO devices can be connected through different physical switches but be tricked into thinking that they are connected to one. It is a similar concept as subnets. 

      4. What is a metric?
                A metric is a unit of measurement which helps a router determine the best path possible for data. There are multiple metrics which can be used and combined in order to determine the best path such as measuring link use, connection speed, reliability, bandwidth, current load, hops etc

      5.What is ARP/RARP?
                ARP stands for Address Resolution Protocol. RARP stands for Reverse Address Resolution Protocol. ARP uses a request for an IP address and translates it to a MAC address. So computer A might say, I want to speak with 192.168.1.55 and the ARP table will tell it that 192.168.1.55 is at FF:23:AB:9A:BC. RARP works the exact opposite. Something may say “hi, I’m FF:23:AB:9A:BC I need an IP, they will then have an IP assigned to them.

6.    What is a default route?

                 A default route is the network route which a router uses when it doesn’t know the route for a IP packet's destination address.

     7. What is a MAC address?
                MAC stands for Media Access Control. This is a unique identifier which is assigned to network interfaces. Whether they are wired or wireless each has its own MAC. This pertains to phones, computers, laptops, TV’s etc. They are formed by regulations made by the IEEE.

     8.  What is a broadcast storm?
                A broadcast storm is essentially like a fork bomb on switches. A node will ask switch C what the address for node A is. If switch C doesn’t know it will ask another node, that node then asks another. Each of those nodes re-broadcast the message from all of the previous nodes, therefore sending simultaneous responses and requests to the previous nodes which then in turn broadcast out their answer or question. This ends up causing a large amount of congestion on the network.

    9.   What is the purpose of VRRP?
                Virtual Router Redundancy Protocol (VRRP) was designed to increase the availability of the default Gateway. This will allow it to provide service to hosts on the same subnet. This increased reliability is achieved through the process of advertising a virtual router which the nodes can utilize. This requires multiple Routers to pull off. One will act as a master and the other is a slave which takes over if the master goes down.

    10.What is a runt, Giant, and collision?
                A runt is a packet which is typically malformed causing it to be too small to traverse the network. Ethernet and other protocols, often require that packets be a minimum number of bytes in order to move across the network.

                A Giant is the exact opposite; it is a packet which is too large to move across the network in a certain protocol. These also are caused by faulty equipment or mal formed packets. These however can be created by accident by a person with malicious intent accidentally setting a setting too high while trying to flood a network.
                With regards to all traffic over the network, nodes determine when the network is available .Sometimes two nodes in different places try to send data at the same time. When this happens the same result will happen as if two people are trying to walk into the same house door at the same time. BANG! A collision.

11.   Describe a TCP connection sequence.

                3 way handshake is the more common term for this. ACK SYN SYNACK. These are Acknowledgement, Synchronization, and Synchronization Acknowledgement. So machine one says “Hey I’d like to communicate with you” Machine 2 says “Ok, this is the message number x you need to get from me so that we are communicating on the same level” then machine one says “Ok message number x” then they both can communicate with each other.

    12.What is the difference between TCP and UDP?

                TCP (Transmission Control Protocol) offers error correction regarding messages it sends. This makes it one of the most popular protocols used on the internet and in networking in general.

                UDP (User Datagram Protocol) however, does not offer this error checking, yet it is still highly used. Why? You may ask. It is because there are things like audio and video which we stream which would get messed up if the receiver were to say to the sender that it needed packet xyz re-sent because the data wasn’t complete. 

                                                              

13.   What is the difference between a hub, switch, and router?

                A Switch learns and directs traffic to the correct users. It does this by reading the physical address where the packets are being sent to and sends it to the corresponding machine based on its switch table. The switch table is a table which consists of a physical address and which switch port the address is plugged into.

                Like a switch a hub connects multiple LAN segments and sends traffic from one place to another. The difference though is that a hub sends all traffic to all of its ports. So even if message xyz is supposed to go to the computer on port 1 it will be broadcasted to port 1, 2, 3, 4, 5, 6, 7, and 8. Or however many ports you have.

                Routers connect different segments of networks as opposed to different segments of LANs. They also connect different networks to other networks. For instance you can have a 177.145.211.0 network connected to a 177.155.234.0 network. They use the actual IP to determine where to direct traffic. What is different about routers though is that they can be secured much more dynamically than switches (hubs have virtually no security). For instance a router connects a home network to the ISP and performs NAT (network address translation) as a security feature.