protocol

Basic CCNA Job Interview Questions

1: What is unicast and how does it work?

Unicast is a one-to-one transmission method. A single frame is sent from the
source to a destination on a network. When this frame is received by the switch,
the frame is sent on to the network, and the network passes the frame to its
destination from the source to a specific destination on a network.

ccna interview questions

2: What is multicast and how does it work?

** Multicast is a one-to-many transmission method. A single frame is sent from
the source to multiple destinations on a network using a multicast address. When
this frame is received by the switch, the frame is sent on to the network and the
network passes the frame to its intended destination group.

3: What is broadcast and how does it work?

** Broadcast is a one-to-all transmission method. A single frame is sent from the
source to a destination on a network using a multicast address. When this frame
is received by the switch, the frame is sent on to the network. The network
passes the frame to all nodes in the destination network from the source to an
unknown destination on a network using a broadcast address. When the switch
receives this frame, the frame is sent on to all the networks, and the networks
pass the frame on to all the nodes. If it reaches a router, the broadcast frame is
dropped.

4: What is fragmentation?

** Fragmentation in a network is the breaking down of a data packet into smaller
pieces to accommodate the maximum transmission unit (MTU) of the network.

5: What is MTU? What’s the MTU for traditional Ethernet?

** MTU is the acronym for maximum transmission unit and is the largest frame
size that can be transmitted over a network. Messages longer than the MTU
must be divided into smaller frames. The network layer (Layer 3) protocol
determines the MTU from the data link layer (Layer 2) protocol and fragments the
messages into the appropriate frame size, making the frames available to the
lower layer for transmission without further fragmentation. The MTU for Ethernet
is 1518 bytes.

6: What is a MAC address?

** A MAC address is the physical address of a network device and is 48 bits (6
bytes) long. MAC addresses are also known as physical addresses or hardware
addresses.

7: What is the difference between a runt and a giant, specific to traditional
Ethernet?

** In Ethernet a runt is a frame that is less than 64 bytes in length, and a giant is
a frame that is greater than 1518 bytes in length. Giants are frames that are
greater than the MTU used, which might not always be 1518 bytes.

8: What is the difference between store-and-forward and cut-through
switching?

** Cut-through switching examines just the frame header, determining the output
switch port through which the frame will be forwarded. Store-and-forward
examines the entire frame, header and data payload, for errors. If the frame is
error free, it is forwarded out its destination switch port interface. If the frame has
errors, the switch drops the frame from its buffers. This is also known as
discarding the frame to the bit bucket.

9: What is the difference between Layer 2 switching and Layer 3 switching?

* * Layer 2 switches make their forwarding decisions based on the Layer 2 (data
link) address, such as the MAC address. Layer 3 switches make their forwarding
decisions based on the Layer 3 (network) address.

10: What is the difference between Layer 3 switching and routing?

** The difference between Layer 3 switching and routing is that Layer 3 switches
have hardware to pass data traffic as fast as Layer 2 switches. However, Layer 3
switches make decisions regarding how to transmit traffic at Layer 3 in the same
way as a router. A Layer 3 switch cannot use WAN circuits or use routing
protocols; a router is still required for these functions.

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CCNA – EIGRP Questions

Here you will find answers to EIGRP Questions

Question 2:

As a Cisco technician, you need to know EIGRP protocol very well. Which of the following is true about EIGRP successor routes? (Choose two)

A – A successor route is used by EIGRP to forward traffic to a destination
B – Successor routes are stored in the neighbor table following the discovery process
C – Successor routes are flagged as “active” in the routing table
D – A successor route may be backed up by a feasible successor route

Answer: A D

Explanation:

B is not correct because neighbor table only contains a list of directly connected EIGRP routers that have an adjacency with this router, it doesn’t contain successor routes.

C is not correct because successor routes are not flagged as “active”, they are always the best route to reach remote networks and are always used to send packets.

A and D are correct because successor route is the best and primary route to a remote network. It is stored in the routing table and topology table. If this route fails, a backup route (called feasible successor route) in the topology table will be used to route traffic to a destination.

Question 3:

Which two statements are true regarding EIGRP? (Choose two)

A – Passive routes are in the process of being calculated by DUAL
B – EIGRP supports VLSM, route summarization, and routing update authentication
C – EIGRP exchanges full routing table information with neighboring routers with every update
D – If the feasible successor has a higher advertised distance than the successor route, it becomes the primary route
E – A query process is used to discover a replacement for a failed route if a feasible successor is not identified from the current routing information

Answer: B E

Explanation:

Diffusing Update Algorithm (DUAL) is the algorithm for selecting and maintaining the best path to each remote network. DUAL tracks all the routes advertised by neighbors and selects routes based on feasible successors. It inserts lowest cost paths into the routing table (these routes are known as primary routes or successor routes) -> A is not correct.

EIGRP is still a distance-vector protocol, but has certain features that belong to link-state algorithms (like OSPF) than distance-vector algorithms. For example, EIGRP sends a partial routing table update, which includes just routes that have been changed, not the full routing table like distance-vector algorithms -> C is not correct.

The feasible successor route will become the primary route when its advertised distance is higher than the feasible distance of the successor route. The feasible successor route can be used in the event that the successor route goes down. Notice that the feasible successor route does not get installed in the routing table but is kept in the topology table as a backup route -> D is not correct.

“Support VLSM, route summarization, and routing update authentication” are the features of EIGRP -> B is correct.

When a route fails and has no feasible successor, EIGRP uses a distributed algorithm called Diffusing Update Algorithm (DUAL) to discover a replacement for a failed route. When a new route is found, DUAL adds it to the routing table -> E is correct.

CCNA – OSPF Questions

Question 1:

Which of the following statements below best describe the process identifier that is used to run OSPF on a router? (Choose two)

A – It is an optional parameter required only if multiple OSPF processes are running on the router
B – It is locally significant
C – It is needed to identify a unique instance of an OSPF database
D – All routers in the same OSPF area must have the same process ID if they are to exchange routing information

Answer: B C

Question 3:

Which items are correct about the routing protocol OSPF? (Choose three)

A – Support VLSM
B – Increase routing overhead on the network
C – Confine network instability to one area of the network
D – Allow extensive control of routing updates

Answer: A C D

Explanation:

Routing overhead is the amount of information needed to describe the changes in a dynamic network topology. All routers in an OSPF area have identical copies of the topology database and the topology database of one area is hidden from the rest of the areas to reduce routing overhead because fewer routing updates are sent and smaller routing trees are computed and maintained (allow extensive control of routing updates and confine network instability to one area of the network).

Question 4:

Which three features are of OSPF routing protocol? (Choose three)

A – Converge quickly
B – OSPF is a classful routing protocol
C – Identify the best route by use of cost
D – Before exchanging routing information, OSPF routers find out neighbors

Answer: A C D

Question 5:

OSPF routing uses the concept of areas. What are the characteristics of OSPF areas? (Chose three)

A – Each OSPF area requires a loopback interface to be configured
B – Areas may be assigned any number from 0 to 65535
C – Area 0 is called the backbone area
D – Hierarchical OSPF networks do not require multiple areas
E – Multiple OSPF areas must connect to area 0
F – Single area OSPF networks must be configured in area 1

Answer: B C E

Explanation:

I used to think the answers should be C D E and here is my explanation:

OSPF can use an active interface for its router ID, so a loopback interface is not a must -> A is incorrect.

OSPF Area is a 32-bit number so we can use up to 2³² – 1 = 4294967296 – 1 (since Area 0 is the first area). Remember that only process ID is a 16-bit number and ranges from 1 to 65535 -> B is incorrect.

F is incorrect too because single area OSPF netwoks must be configured in Area 0, which is called the backbone area.

For answer D, it is a bit hard to guess what they want to say about “hierarchical” but we should understand “Hierarchical OSPF networks” as “OSPF networks”. D is correct bercause we can only have one area (area 0 – the backbone area) for our networks.

But TT commented on 01-11-2010:

Especially to note on choice B, D, and E:

Choice B: we all know that The areas can be any number from 0 to 4.2 billion and 1 to 65,535 for the Process ID. As choice B specifies ‘area’ (be aware, it’s not saying ‘process id), there is no reason to say that we cannot assign numbers from 0 to 65535 for area # (it is using ‘may be’, not ‘have to be’ or ‘ought to be’). Hence, we do not worry about assigning ’0′.

Choice E: as Area 0 is the backbone, we all understand that any areas in a OSPF network have to be connected to it. And actually this is implicitly saying that multiple areas form a hierarchical OSPF network, as Area 0 being a root and others being its leaves.

Choice D: when it specifies ‘Hierarchical’, at least 2 areas should be required to form such topology (of course that includes Area 0)

Although Choice B is not an absolutely accurate statement since it not only can be assigned up to 65535, it is still a correct answer. And again, it specifies ‘area’, not ‘process id’, so ’0′ can be included. Finally, it would be meaningless to call OSPF a hierarchical network if no more than one area is present.