Networking

What is a NIC?
Ans: A network interface card, more commonly referred to as a NIC, is a device that allows computers to be joined together in a LAN, or local area network. Networked computers communicate with each other using a given protocol or agreed-upon language for transmitting data packets between the different machines, known as nodes. The network interface card acts as the liaison for the machine to both send and receive data on the LAN.
The most common language or protocol for LANs is Ethernet, sometimes referred to as IEEE 802.3.
Note: Ethernet is a standard communications protocol embedded in software and hardware devices, intended for building a local area network.

What is a MAC Address?
MAC address ( Media Access Control) is a unique value associated with a Network Interface Card. MAC address is also known as Hardware address or Physical Address. MAC address uniquely identifies a Network adaptor in the LAN.
MAC addresses are 48 bits in length.

When would you use a crosslink cable?
Cross link cables are used to connect a PC to PC, this cable is special because there are a few wires switched that allow the computer to send and receive data packets with Network card.

What is the difference between a Hub and a Switch?
A hub is typically the least expensive, least intelligent, and least complicated device than Switch. Its job is very simple: anything that comes in one port is sent out to the others. Every computer connected to the hub "sees" everything that every other computer on the hub sees. The hub itself is blissfully ignorant of the data being transmitted.
A switch does essentially what a hub does but more efficiently. By paying attention to the traffic that comes across it, it can "learn" where particular addresses are. For example, if it sees traffic from machine A coming in on port 2, it now knows that machine A is connected to that port and that traffic to machine A needs to only be sent to that port and not any of the others. The net result of using a switch over a hub is that most of the network traffic only goes where it needs to rather than to every port. On busy networks this can make the network significantly faster.

On which OSI layer can a router be found?
The OSI layer 2 and layer 3 router provides additional intelligence to networks by implementing the data link and network layers of the OSI model. The data link layer describes the logical organization of data bits transmitted on a particular medium; for example, this layer defines the framing, addressing, and cyclic redundancy checks of Ethernet packets. The network layer describes how a series of exchanges over various data links delivers data between any two nodes in a network and defines the addressing and routing structure of the Internet.

What is CSMA/CD?
CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is the protocol used in Ethernet Network to ensure that only one network node is transmitting on the network wire at any one time.

What is multicast?
Multicasting may be used for streaming multimedia, video conferencing, shared white boards and more as the internet grows. Multicasting is still new to the internet and not widely supported by routers. New routing protocols are being developed to enable multicast traffic to be routed. Some of these routing protocols are:
Hierarchical Distance Vector Multicast Routing Protocol (HDVMRP)
Multicast Border Gateway
Protocol Independent Multicast
An IP multicast address is in the range 224.0.0.0 through 239.255.255.255.

What is Broadcast?

Broadcast - A transmission to all interface cards on the network.
RFC 919 and 922 describe IP broadcast datagrams as,

Limited Broadcast - Sent to all NICs on the some network segment as the source NIC. It is represented with the 255.255.255.255 TCP/IP address. This broadcast is not forwarded by routers so will only appear on one network segment.
Direct broadcast - Sent to all hosts on a network. Routers may be configured to forward directed broadcasts on large networks. For network 192.168.0.0, the broadcast is 192.168.255.255.

Below mentioned are examples of broadcast
ARP on IP
DHCP on IP
Routing table updates. Broadcasts sent by routers with routing table updates to other routers.

The ethernet broadcast address in hexadecimal is FF:FF:FF:FF:FF:FF.
There are several types of IP broadcasting:
The IP limited broadcast address is 255.255.255.255. This broadcast is not forwarded by a router.
A broadcast directed to a network has a form of x.255.255.255 where x is the address of a Class A network. This broadcast may be forwarded depending on the router program.
A broadcast sent to all subnetworks. If the broadcast is 10.1.255.255 on network 10.1.0.0 and the network is subnetted with multiple networks 10.1.x.0, then the broadcast is a broadcast to all subnetworks.
A broadcast sent to a subnet in the form 10.1.1.255 is a subnet broadcast if the subnet mask is 255.255.255.0.

What is the difference between TCP and UDP?
Describe some of the settings that are added by TCP and by UDP to the packet's header.
What are TCP Ports? Name a few.
What is a TCP Session?
What three elements make up a socket?
What will happen if you leave the default gateway information empty while manually configuring TCP/IP?
What will happen if you execute the following command: "arp –d *"?
What is ICMP?
When would you use the ping command with the "-t" switch?