39: Explain the functionality of a switch.
Answer:
When a switch is turned on and receives frames on its port, it learns its source and destination MAC addresses and stores the same in MAC table with respective switch port details. If a frame is broadcast or multicast frame, switch forwards the same across all the switch ports except the port on which the frame is received. If the frame is unicast frame and the destination MAC is unknown, switch forwards the frame to all its port except the port on which the frame was received. Switch waits for response and updates the MAC table once the response is received. This way switch learns MAC addresses of all the PCs connected to its ports. Once the MAC table is fully populated, switch forwards the unicast frames exactly to a specific port and not to all ports.
41: What is VLAN? What is the need of VLAN creation?
Answer:
VLAN stands for Virtual LAN. Due to VLAN configuration even though PCs are not physically connected on a single switch they can be treated as a single LAN. For example, few PCs connected on first floor and few PCs connected on third floor can be configured in single VLAN and hence will be treated as on same LAN segment.
Following are the basic reasons to create VLANs
a) VLANs stop broadcast and do not forward the broadcast frames.
b) Layer 2 switches cannot forward frames into other VLANs which acts as a security feature.
c) Better network traffic management.
53: Explain packet routing mechanism in a router.
Answer:
Router is a layer 3 device (Network layer) and hence analyzes layer 3 information i.e. IP header of the packet. It reads destination IP addresses and performs a look-up in routing table for matching entries. It maintains routing tables which has entries of all the destination subnets and respective interfaces to reach those subnets. Once a relevant entry is found in the routing table, router forwards the IP packet to the destination. In case of multiple routes’ availability to a destination, router selects the best route and forwards IP packets to the destination.
54: What is Static Routing? Explain with syntax.
Answer:
Static Routing is a method of manually configuring router to forward IP packets to destination subnets. By configuring static routes, network administrators can ensure that packets would reach the remote destination.
Syntax/ command for configuring static route is as follows:
router# config t --- This will enable configuration mode
router(config)# ip route X.X.X.X (destination network/host) X.X.X.X (subnet mask) X.X.X.X (next hop)
Though configuring static route is simple, it becomes complicated and difficult to manage as the network grows.
55: What is the other way/Syntax of configuring static route?
Answer:
Static route can be configured by using interface name instead of next hop IP address.
Syntax/ command for configuring static route is as follows
router# config t --- This will enable configuration mode
router(config)# ip route X.X.X.X (destination network/host) X.X.X.X (subnet mask) Interface name ( ex Serial 0/0, Fe 0/1 etc)
93: What are the default administrative distance values for various routing mechanisms?
Answer:
Following are the default administrative distance values assigned to various routing mechanisms:
a) Routes learned from connected interface – 0
b) Routers learned from Static Route – 1
c) Routers learned from EIGRP summary route – 5
d) Routers learned from external BGP – 20
e) Routers learned from EIGRP – 90
f) Routers learned from IGRP – 100
g) Routers learned from OSPF – 110
h) Routers learned from RIP – 120
i) Routers learned from external EIGRP – 170
j) Routers learned from internal BGP – 200
k) Routers learned from an unknown network – 255
145: Compare SRAM vs DRAM?
Answer:
SRAM (Static RAM) is made up of transistors which hold the data till the power supply is on. SRAM needs lot of transistors to store small amount of data. Number of transistors decides the capacity of data storage, hence SRAM is costly compared to DRAM. SRAM is used in CPU as a cache memory for its faster speed of operation. DRAM (Dynamic RAM) needs the data to be refreshed periodically to retain the data. It needs a transistor and a capacitor to hold single bit of data, hence it is cheaper than SRAM. It requires additional circuit in order to refresh DRAM data; hence it is slower than SRAM. It consumes more power than SRAM.
146: What is ROM / PROM / EEPROM ?
Answer:
ROM: Read Only Memory: Its contents can be read / accessed but cannot be altered. Boot program are saved in ROM which instructs computer to load the operating system.
PROM: Programmable Read Only Memory: PROM is a type of ROM which can be programmed once.
EPROM: Erasable Programmable Read Only Memory: ERPOM can be written any number of times. It can be erased and re-written as needed.
