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Network Security Interview Questions

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ARP -Meaning of ARP "Address Resolution Protocol", is used to map ip Network addresses to the hardware (Media Access Control sub layer) addresses used by the data link protocol. The ARP protocol operates between the network layer and the data link layer in the Open System Interconnection (osi) model.

RARP-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. RARP is available for Ethernet, Fiber Distributed-Data Interface, and token ring LANs.

Restricting the users from accessing a set of services within the local area network is called port blocking.

we,ll give you the fine example its nothing but we have to block the switch port with particular maC address..for example we have 8-port switch ,in that first port we connected a machine that belongs to this mac address {4e5a.23bf.34ae.9a4c} and we block the switch port with this mac address for instance you unplug the original host and plug the other one now your new machine will be prevented from accessing switch port thats the idea.... so if u enabling port blocking command in a switch only particular machine or intented machine allow to use access ,other machine will be restricted... port blocking is used for security purpose...otherwise some intruders enter into your company and destroy your lan with single laptop thats it 

When a packet is sent out of a server, It has source and Destination IP, sorcce and destination Port no and sorce and destination Mac ID, first it is sent to the switch, The switch checks the packet whether the MAC ID is in the MAC-Address-Table if not it broad casts the message if the destination IP is not in the same segment Then it forwards the packet to the gateway (normally the router or firewall). then the router/firewall checks its routing table and access lists if it has the information about the destination IP and if it has access to the destination IP it forwards it to the next hop, and if any one of the condition fails it just drops the packet. 

For small lan we use class-c address

Explanation:In class C ip address the first three bytes out of four are for network address while the last byte is for host address which can range from 1-254 which is smallest lan possible whereas class B has two bytes and class A has three bytes reserved for host address which increases number of hosts in those classes 

Found from cisco.com,
Confidentiality, Integrity and Availability

CIA means Certified Internal Auditor.
globally accepted and recognized certificate in the field of internal audits. 

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