IT Certification & Interview Help.

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CCNP Based INTERVIEW QUESTIONS Part 8
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SWITCHING
What are three types of LAN traffic?
Unicasts - intended for one host.
Broadcasts - intended for everyone.
Multicasts - intended for a only a subset or group within an entire network.

What are unicast frames?
Unicast frames are the most common type of network traffic. A unicast frame is a frame intended for only one host. The only station that processes this frame is one station that has its own MAC address in the destination portion of packet.

What are broadcast frames?
Broadcast frames are frames intended for everyone. Stations view broadcast frames as public service announcements. All stations receive and process broadcast frames. In large networks, broadcasts can cause serious performance degradation in network hosts - (broadcast storm).
The destination address of broadcast frames (Data Link / Layer 2 broadcast addresses is FF-FF-FF-FF-FF-FF or alternatively all 1s in binary (11111111).

What are multicast frames?
Multicast frames address a group of devices that have a common interest. These frames allow the source to send only one copy of the frame on the network even though it is intended for several stations. Only stations that have a card that is configured by software to receive multicast frames for a particular multicast group can process a frame to that multicast address - all other stations discard multicast frames
What three major functions do Data Link Layer / Layer 2 Switches perform?
Address learning
Packet forwarding/filtering
Loop avoidance by spanning tree

What will occur when you attempt to segment a network with hubs and repeaters?
Basically, hubs and repeaters become extensions of the physical cable plant. All devices that connect to either a hub or a repeater share the same bandwidth and by definition hubs and repeaters create a single broadcast and collision domain.
Think of both devices are pass-through devices much like a electrical power-strip. Hubs and repeaters reside on the Physical Layer / Layer 1 of the OSI model where they pass 0s and 1s along the wire or up to the Data Link Layer. CSUs / Channel Service Units fall into the same category. All are regarded as unintelligent devices. No addressing takes place on the Physical layer.
What three devices are used to segment a LAN?
Router - logical addressing - IP address
Switch - physical addressing - MAC address
Bridge - physical addressing - MAC addres

What is microsegmentation?
Each workstation or network device on the network has its own dedicated segment - also known as a Collision Domain - to a switch. Each device gets the segments full bandwidth and does not have to share the dedicated segment with other devices. Collisions are reduced because each segment is its own Collision Domain.
Important: Full-duplex transmission is achieved by microsegmentation. Each device can send and receive at the same time which doubles the amount of bandwidth between nodes.
What are the three switching methods in Cisco Catalyst switches?
The three frame operating modes to handle frame switching are
Store-and-forward
Cut-through
Fragment-free

What is the Cisco Catalyst store-and-forward switching method?
In the store-and-forward switching method, the switch receives the entire frame before it forwards it. The switch reads the cyclic redundancy check (CRC) to make sure the frame is not bad. If the frame is good, the switch forwards it. Because the switch stores the frame before forwarding it, latency is introduced in the switch. Latency through the switch varies with the size of the frame.

What is the Cisco Catalyst cut-through switching method?
In cut-through switching mode, the switch only checks the frame's destination address and immediately begins forwarding the frame out the appropriate port. Because the switch checks the destination address in only the header and not the entire frame, the switch forwards a collision frame or a frame that has a bad CRC.

What is the Cisco Catalyst fragment-free switching method?
Also known as modified cut-through, fragment-free switching checks the first 64 bytes before forwarding the frame. Ethernet specifications state that collisions should be detected during the first 64 bytes of the frame. By reading the first 64 bytes of the frame, the switch can filter most collisions, although late collisions are still possible.


What is the default switching mode in Cisco Catalyst 1900 switches?
The default switching mode for the Catalyst 1900 is fragment-free.

What is half-duplex transmission mode?
Half-duplex transmission is the default mode that Ethernet functions in. In half-duplex transmission, a device can only send or receive--not do both at once. In half-duplex mode, stations are susceptible to collisions, and efficiency is rated at 50 to 60 percent.
What is full-duplex transmission mode?
In full-duplex mode, a station can send and receive at the same time. In full-duplex mode, collision detection is disabled. This mode offers 100 percent efficiency in both directions.
On a Cisco Catalyst 1900 switch, what are the default duplex settings for 10BaseT/100BaseT ports, default switching mode, and default protocols?

What are dynamic addresses on a Catalyst switch?
Dynamic addresses are addresses that the switch learns about dynamically through the learning process. If the switch does not see a MAC address for a certain amount of time, it drops the MAC address.


What are permanent MAC addresses on a Catalyst switch?
Permanent MAC addresses are entered manually by the administrator and are not aged out.