Microsoft Certified Systems Engineer (MCSE) Interview Preparation Guide

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.

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

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.

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.

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.

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.

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

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

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.

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