Technical Interview Questions Active Directory and Networking 2016.
What is an IP address?
Every device connected to the public Internet is assigned a unique number known as an
Internet Protocol (IP) address. IP addresses consist of four numbers separated by periods (also
called a ‘dotted-quad’) and look something like 127.0.0.1.
In computer networking, an Internet Protocol (IP) address consists of a numerical
identification (logical address) that network management assigns to devices participating in a
computer network utilizing the Internet Protocol for communication between its nodes.
Although computers store IP addresses as binary numbers, they often display them in more
human-readable notations, such as 192.168.100.1 (for IPv4), and 2001:db8:0:1234:0:567:1:1
(for IPv6). The role of the IP address has been characterized as follows: “A name indicates
what we seek. An address indicates where it is. A route indicates how to get there.” 
What is subnet Mask ?
A subnet (short for “subnetwork”) is an identifiably separate part of an organization’s
network. Typically, a subnet may represent all the machines at one geographic location, in
one building, or on the same local area network (LAN). Having an organization’s network
divided into subnets allows it to be connected to the Internet with a single shared network
address. Without subnets, an organization could get multiple connections to the Internet, one
for each of its physically separate subnetworks, but this would require an unnecessary use of
the limited number of network numbers the Internet has to assign. It would also require that
Internet routing tables on gateways outside the organization would need to know about and
have to manage routing that could and should be handled within an organization.
What is ARP? What is ARP Cache Poisoning?
Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP
address) to a physical machine address that is recognized in the local network. For example,
in IP Version 4, the most common level of IP in use today, an address is 32 bits long. In an
Ethernet local area network, however, addresses for attached devices are 48 bits long. (The
physical machine address is also known as a Media Access Control or MAC address.) A
table, usually called the ARP cache, is used to maintain a correlation between each MAC
address and its corresponding IP address. ARP provides the protocol rules for making this
correlation and providing address conversion in both directions.
How ARP Works
When an incoming packet destined for a host machine on a particular local area network
arrives at a gateway, the gateway asks the ARP program to find a physical host or MAC
address that matches the IP address. The ARP program looks in the ARP cache and, if it finds
the address, provides it so that the packet can be converted to the right packet length and
format and sent to the machine. If no entry is found for the IP address, ARP broadcasts a
request packet in a special format to all the machines on the LAN to see if one machine
knows that it has that IP address associated with it. A machine that recognizes the IP address
as its own returns a reply so indicating. ARP updates the ARP cache for future reference and
then sends the packet to the MAC address that replied.
Since protocol details differ for each type of local area network, there are separate ARP
Requests for Comments (RFC) for Ethernet, ATM, Fiber Distributed-Data Interface,
HIPPI, and other protocols.
There is a Reverse ARP (RARP) for host machines that don’t know their IP address. RARP
enables them to request their IP address from the gateway’s ARP cache.
RARP (Reverse Address Resolution Protocol) is a protocol by which a physical machine in a
local area network can request to learn its IP address from a gateway server’s Address
Resolution Protocol (ARP) table or cache. A network administrator creates a table in a local
area network’s gateway router that maps the physical machine (or Media Access Control –
MAC address) addresses to corresponding Internet Protocol addresses. When a new machine
is set up, its RARP client program requests from the RARP server on the router to be sent its
IP address. Assuming that an entry has been set up in the router table, the RARP server will
return the IP address to the machine which can store it for future use.
What is a default gateway? What happens if I don’t have one?
a gateway is a routing device that knows how to pass traffic between different subnets and
networks. A computer will know some routes (a route is the address of each node a packet
must go through on the Internet to reach a specific destination), but not the routes to every
address on the Internet. It won’t even know all the routes on the nearest subnets. A gateway
will not have this information either, but will at least know the addresses of other gateways it
can hand the traffic off to. Your default gateway is on the same subnet as your computer, and
is the gateway your computer relies on when it doesn’t know how to route traffic.
The default gateway is typically very similar to your IP address, in that many of the numbers
may be the same. However, the default gateway is not your IP address. To see what default
gateway you are using, follow the steps below for your operating system.
Can a workstation computer be configured to browse the Internet and yet NOT have a
What is a subnet?
In computer networks based on the Internet Protocol Suite, a subnetwork, or subnet, is a
portion of the network’s computers and network devices that have a common, designated IP
address routing prefix (cf. Classless Inter-Domain Routing, CIDR).
A routing prefix is the sequence of leading bits of an IP address that precede the portion of the
address used as host identifier (or rest field in early Internet terminology).
What is APIPA?
What is Automatic Private IP Addressing (APIPA)?
A. Windows 98, 98 SE, Me, and 2000 have an Automatic Private IP Addressing (APIPA)
feature that will automatically assign an Internet Protocol address to a computer on which it
installed. This occurs when the TCP/IP protocol is installed, set to obtain it’s IP address
automatically from a Dynamic Host Configuration Protocol server, and when there is no
DHCP server present or the DHCP server is not available. The Internet Assigned Numbers
Authority (IANA) has reserved private IP addresses in the range of 169.254.0.0 –
169.254.255.255 for Automatic Private IP Addressing.