Interview Question

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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Autonomous System (AS)

1. What is an Autonomous System?

An Autonomous System (AS) is a group of IP networks operated by one or more network operator/s which has a single and clearly defined external routing policy. Exterior routing protocols are used to exchange routing information between Autonomous Systems.

2.When should an Autonomous System be created?

An AS needs to be created if a network connects to more than one AS with different routing policies. Some common examples of Autonomous Systems are networks connected to two or more upstream service providers or exchange points, networks peering locally at exchange points.

3.What is an Autonomous System Number?

A public AS has a globally unique number, an Autonomous System number (ASN), associated with it; this number is used in both the exchange of exterior routing information (between neighboring Autonomous Systems), and as an identifier of the AS itself.

There are two types of Autonomous System numbers; Public AS numbers and Private AS numbers.

4.When is a Public Autonomous System number required?

A Public AS number is required only when an AS is exchanging routing information with other Autonomous Systems on the public Internet. That is, all routes originating from an AS is visible on the Internet.

5. Am I eligible for a Public Autonomous System Number?

An organisation is eligible for an ASN assignment if it:

is multihomed (this includes organisations connected to a public Internet Exchange Point); and
has a single, clearly defined routing policy that is different from its providers’ routing policies.

An organisation will also be eligible if it can demonstrate that it will meet the above criteria upon receiving an ASN (or within a reasonably short time thereafter).

6. When can I use a Private Autonomous System number?

A Private AS number should be used if an AS is only required to communicate via BGP with a single provider. As the routing policy between the AS and the provider will not be visible in the Internet, a Private AS Number can be used for this purpose.

The IANA has reserved AS64512 through to AS65535 to be used as private ASNs.

7. I plan to change my upstream providers – can I take my ASN with me?

This depends on how you received that ASN. If you got it directly from APNIC or an NIR, then it is portable and you can take it with you to whichever providers you choose (subject to the agreement you signed with APNIC or the NIR).

However if got your ASN from an LIR, you can only use it while you continue to receive connectivity from the LIR. In other words, if you decide to no longer use that LIR as one of your upstream providers, then you will have to return the ASN.

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Why we use Trunk Port

Question : We can connect two switches via Ethernet cable why we use trunk port between switches ?

Ans:

Trunk links are required to pass VLAN information between switches. A port on a Cisco switch is either an access port or a trunk port. Access ports belong to a single VLAN and do not provide any identifying marks on the frames that are passed between switches. Access ports also carry traffic that comes from only the VLAN assigned to the port. A trunk port is by default a member of all the VLANs that exist on the switch and carry traffic for all those VLANs between the switches. To distinguish between the traffic flows, a trunk port must mark the frames with special tags as they pass between the switches. Trunking is a function that must be enabled on both sides of a link. If two switches are connected together, for example, both switch ports must be configured for trunking, and they must both be configured with the same tagging mechanism (ISL or 802.1Q).

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How many VLAN Create on Router

Ans : Vlan create on Switches not router :p

All the following information is taken from the data sheets for these devices, on the Cisco website.

The Cisco Catalyst 3550 switches support up to 1,005 VLANs.
The Cisco Cataylst 3750 switches support up to 1,005 VLANs per stack.

Both support up to 4000 VLAN IDs, but only 1,005 VLANs configured on these (some VLAN IDs will come from other switches). Unless you are a service provider, you will never configure anything like these numbers.

Please also note that the 3550 is now end-of-life, you should look at the 3560 switches instead.

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Private IP Classes Range

Public IP addresses are addresses that are valid as nodes on the Internet.
They can be resolved and routed across the Internet from one point to another.
Unlike public IP, private IP addresses are not valid on the Internet.

Three range of private IP addresses has been selected for the three network class.

For Class A network, 10.0.0.0 – 10.255.255.255 (10/8 prefix) range (For big network that requires a huge pool of 16 million private IP addresses)

For Class B network, 172.16.0.0 – 172.31.255.255 (172.16/12 prefix) range (For medium-sized network that requires 65000 private IP addresses)

For Class C network, 192.168.0.0 – 192.168.255.255 (192.168/16 prefix) range (Commonly used IP range on smaller network for easier addressing of 254 IP addresses. May not necessarily be smaller network but network managed in smaller blocks.)

private ip classes range

Beside these, there is Microsoft’s 169.254.0.0 range of default IP addresses that are allocated to systems when they are unable to obtain address from a DHCP server. Its Called APIPA

When a DHCP server fails, APIPA allocates IP addresses in the private range 169.254.0.1 to 169.254.255.254.

Category - Interview Question

1. What is an Autonomous System?

2.When should an Autonomous System be created?

3.What is an Autonomous System Number?

4.When is a Public Autonomous System number required?

5. Am I eligible for a Public Autonomous System Number?

6. When can I use a Private Autonomous System number?

7. I plan to change my upstream providers – can I take my ASN with me?