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Networking interview - October 14, 2008 at
18:10 pm by Rajmeet Ghai
What is the use of IGMP protocol?
Internet Group Management Protocol: - It allows internet
hosts to participate in multicasting. The IGMP messages are
used to learn which hosts is part of which multicast groups.
The mechanism also allow a host to inform its local router,
that it wants to receive messages.
What are Ping and Tracert?
Ping and tracert are the commands used to send information
to some remote computers to receive some information.
Information is sent and received by packets. Ping I
particularly used to check if the system is in network or not.
It also gives packet lost information. In windows ping command
is written as ping ip_address Tracert is called as trace
route. It is used to track or trace the path the packet takes
from the computer where the command is given until the
destination. In windows ping command is written as tracert
ip_address
Explain RSVP. How does it work?
Resource Reservation protocol is used to reserve resources
across a network. It is used for requesting a specific Quality
of Service (QoS) from the network. This is done by carrying
the request (that needs a reservation of the resource) of the
host throughout the network. It visits each node in the
network. RSVP used two local modules for reservation of
resources. Admission control module confirms if there are
sufficient available resources while policy module checks for
the permission of making a reservation. RSVP offers
scalability. On a successful completion of both checks RSVP
uses the packet classifier and packet scheduler for the
desired Qos requested.
Explain the concept of DHCP.
Dynamic Host Configuration Protocol is used assigning IP
addresses to computers in a network. The IP addresses are
assigned dynamically. Certainly, using DHCP, the computer will
have a different IP address every time it is connected to the
network. In some cases the IP address may change even when the
computer is in network. This means that DHCP leases out the IP
address to the computer for sometime. Clear advantage of DHCP
is that the software can be used to manage IP address rather
than the administrator.
What are the differences between a domain and a
workgroup?
In a domain, one or more computer can be a server to manage
the network. On the other hand in a workgroup all computers
are peers having no control on each other. In a domain, user
doesn’t need an account to logon on a specific computer if an
account is available on the domain. In a work group user needs
to have an account for every computer.
In a domain,
Computers can be on different local networks. In a work group
all computers needs to be a part of the same local
network.
Explain how NAT works.
Network Address Translation translates and IP address used
in a network to another IP address known within another
network. A NAT table is maintained for global to local and
local to mapping of IP’s. NAT can be statically defined or
dynamically translate from a pool of addresses. The NAT router
is responsible for translating traffic coming and leaving the
network. NAT prevents malicious activity initiated by outside
hosts from reaching local hosts by being dependent on a
machine on the local network to initiate any connection to
hosts on the other side of the router.
What is PPP protocol? Explain PPP packet format.
Point to Point protocol helps communication between 2
computers over a serial cable, phone line or other fiber optic
lines. E.g. Connection between an Internet Service Provider
and a host. PPP also provides authentication. PPP operates by
sending Request packets and waiting for Acknowledge packets
that accept, reject or try to change the request. The protocol
is also used to negotiate on network address or compression
options between the nodes.
Packet format:-
Flag field: 1 byte: - Indicates frames beginning or
end
Address field: 1 byte: - Used for broadcast address
(destination address)
Control field: 1 byte: - Used as a
control byte
Protocol field: - 1 or 2 bytes: - Setting of
protocol in information field (of datagram)
Information: -
0 or more bytes: - Datagram (whether it contains data or
control information)
Padding: - 0 or more bytes: - optional
padding
FCS: - 2 or more bytes: - error check sum
What is IP Spoofing and how can it be prevented?
IP spoofing is a mechanism used by attackers to gain
unauthorized access to a system. Here, the intruder sends
messages to a computer with an IP address indicating that the
message is coming from a trusted host. This is done by forging
the header so it contains a different address and make it
appear that the packet was sent by a different machine.
Prevention:-
Packet filtering: - to allow packets with
recognized formats to enter the network
Using special
routers and firewalls.
Encrypting the session
Explain IP datagram, Fragmentation and MTU.
IP datagram can be used to describe a portion of IP data.
Each IP datagram has set of fields arranged in an order. The
order is specific which helps to decode and read the stream
easily. IP datagram has fields like Version, header length,
Type of service, Total length, checksum, flag, protocol, Time
to live, Identification, source and destination ip address,
padding, options and payload.
MTU:- Maximum Transmission Unit is the size of the largest
packet that a communication protocol can pass. The size can be
fixed by some standard or decided at the time of
connection
Fragmentation is a process of breaking the IP packets into
smaller pieces. Fragmentation is needed when the datagram is
larger than the MTU. Each fragment becomes a datagram in
itself and transmitted independently from source. When
received by destination they are reassembled.
What is an application gateway?
An application gateway is an application program that runs
on a firewall between two networks. An application gateway is
used for establishing connection between client program and
destination service. The client negotiates with the gateway to
communicate with the service of destination. Here, gateway can
be called as a proxy. Hence, two connections are made. One
between client and proxy; other, between proxy and destination
service. Connections take place behind the firewall
Explain Circuit Level Gateway.
A circuit level gateway is used to find if a session in TCP
handshaking is legitimate or not. It can be considered as a
layer between application layer and transport layer. They
protect the information of the private network they protect.
Circuit level gateways do not filter packets.
What is 'Gateway Of Last Resort'?
A Gateway of Last Resort or Default gateway is a route used
by the router when no other known route exists to transmit the
IP packet. Known routes are present in the routing table.
Hence, any route not known by the routing table is forwarded
to the default route. Each router which receives this packet
will treat the packet the same way, if the route is known,
packet will be forwarded to the known route.
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