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Prepare for Networking/ Network Security Interview-Refer these questions :)

Networking  Questions
OSI Reference Model What are the different network stack models and list all the layers of each model? Answer
What are the functions of Transport, Network and Datalink layers? Answer
What are the different protocols works at each of the layers? Answer
What is end to end communication and Hop to Hop communication?
What is a port number and give some examples. Answer
Explain IP layer ( L3) and IP protocol header
What is fragmentation and explain how IP will handle the fragmentation.
What is the difference between Half-duplex and Full-duplex?
 Define Unicast, Multicast and Broadcast. What is the use of Multicast?
What are the functions of Data link layer, what is the MAC format?
What is a Frame, explain the frame header.
A scenario to explain the packet flow layer wise.
IP Addressing (32 bit & 128 bit) What is IP address and it’s format
What are the different Classes of IP address and give the range of each class
What is network id , broadcast id and subnet mask?
How to find the network id of a given IP address?
What is subnetting and give us a scenario for implementing IP subnetting, a task on subnetting.
What is the difference between FLSM and VLSM?
What is the subnetwork address if the destination address is and the subnet mask is
What is the subnetwork address if the destination address is and the mask is
A company is granted the site address (class C).
The company needs six subnets. Design the subnets.
A company is granted the site address (class B). The company needs 1000 subnets. Design the subnets
Subnetting & VLSM You want to implement class c IP addresses in your, what subnet mask you should implement in your network so that number of subnets will be equal to the number of hosts per subnet?
ARP ARP works at which layer and Why?
Is ARP part of the Ethernet frame?
What is the target IP address in ARP request and ARP reply packet?
GARP What is GARP and how it will be useful?
Difference between ARP and GARP?
What is the target IP address in GARP request and GARP reply packet?
Packet structure of ARP and GARP?
ICMP (Types & Codes)  Explain various ICMP messages?
Which ICMP message confirms the traceroute is completed?
IP Which is the importance of identification field, Flags, Fragment Offset in the IP packet?
Why fragmentation is required?
Which device can reassemble the packet?
How the packet is reassembled?
What is the importance of DF, MF flag?
What is the purpose of fragment offset?
What is the importance of TTL value?
What does the protocol field determines in the IP packet?
How Path MTU Discovery works
TCP (3 way handshake, Windowing, Flow control, Flags, Retranmission, SACK) Explain 3 way handshake process?
Parameters Informed, negotiated in TCP
Fields in TCP header
4 way Close, Simultaneous close
Flow Control- Sliding Windows
Error Control- TCP retransmissions
Congestion Control
What is the importance of sequence number?
How sequence number is calculated?
What is the purpose of acknowledgement number?
What is the difference between Total length and header length?
What does window size indicate?
When the MSS value is getting negotiated?
Explain the control flag?
What is the difference between PUSH and URG flag?
What is the purpose of RST bit?
What is SACK?
Who is responsible for the reliability of UDP packet.
Difference between TCP and UDP.
How MTU is calculated? How does it work?
How MSS is calculated
TCP stage bypass syn check (Juniper) Answer
UDP In a serialized connected network including Router, Switches and Firewall with varied MTU sizes Which device will fragment the packet and what are the sizes of each fragment?
Why Firewall reassembles the packet?
What Firewall verifies after reassembling the packet?
Can reassembly done by intermediate device?
Is fragmentation applicable only for TCP?
Can we fragment packet containing UDP data?
FTP ( Active & Passive) What is the difference between Active and Passive FTP?
What is the important of port command?
Which FTP type is preferred if firewall is blocking the connection?
How active FTP works?
How passive FTP works?
TFTP How TFTP works? Explain the protocols involved.
SNMP (Query & Response, MIB, Communities) What is SNMP?
SNMP versions.
Components of SNMP?
Ports used in SNMP?
Explain MIB?
 Explain how to implement SNMP on a network?
Explain difference between SNMP Query response & SNMP trap?
Ping What are the various instances of getting “Request timed out”?
Difference between destination host unreachable and destination network unreachable?
Explain various ICMP messages?
Traceroute How traceroute works?
What is the difference between traceroute and tracert?
Is traceroute a reliable tool to identify network issues?
Why there are three columns in traceroute results?
Which ICMP message confirms the traceroute is completed?
What does * indicate in traceroute result?
HTTP/S Difference between HTTP & HTTP/S?
DHCP How DHCP works?
What is the reason for getting APIPA address?
How to troubleshoot APIPA issue?
What is the purpose of relay agent?
Is DHCP decline message is sent by Client or Server?
Is DHCPNACK message is sent by Client or server?
How DHCP discover message is being forwarded by router when it is a broadcast message?
DNS Explain zone transfer?
What are the types of records?
What is forward lookup & Reverse lookup?
When will DNS use TCP?
When will DNS use UDP?
Explain DNS quesr process.
Auto Negotiation Explain Auto negotiation.
What is MDI & MDIX ports?
Explain Straight Through & Cross Over cabling. Where will it be used.
Switching Protocols
Layer 2 Ethernet Frames Details
Mac Address table
Blocking,Listening, Learning, Forward, Filter, Aging
ARP Vs Mac Table
Spanning Tree Protocol (RSTP, MSTP)
What is inter vlan routing?
What is sub interface?
What is a broadcast domain and a collision domain
Compare HUB and Switch WRT broadcast and collision domain
What is a MAC address table and how a Switch will build a MAC table, single switch scenario and multiple switch scenario
What is a VLAN and how it will reduce the broadcast traffic
What is the difference between an access port and a trunk port and what are different types of tagging
What is a native VLAN what type of traffic will go through native VLAN
What is STP and why do we need redundant links between switches,
What are the different port states and timers and BPDU
What is bridge id and its format and the Root bridge election criteria
STP convergency with 4 switches, what is the Root port election criteria
What is TCN and TC BPDU and STP reconvergency
Can you explain the ARP Header with the fields?
What are the changes a frame undergoes in a switch
Routing Concepts
What is a routing table?
Define static routing & dynamic routing?
What is a default route?
What is a route metric?
What is the difference between routing and routed protocol? Give examples.
What is route lookup process, parent and child route
What is the effect of IP classless and classfull on routing
What are the different type of routing table entries and Admin distance
What are the different types of routing protocols and list for each type
What do you understand by backbone area?
What is the need for dividing the autonomous system into various areas?
What is the benefit of dividing the entire network into areas?
What changes it would make if the network is divided or not divided into areas?
What is the purpose of Stub area?
What is the purpose of NSSA area?
How Stub and NSSA works?
What are the criteria to form neighbour ship?
Why master slave needs to be elected between two neighbour interface?
What is virtual link?
Virtual link updates are multicast or unicast?
Explain the various states of OSPF?
What are various LSA and message Types?
What is the difference between E1 an E2 metrics?
Explain router redistribution?
How DR and BDR is elected?
Difference between eBGP and iBGP?
What is the TCP port number for BGP communication?
Explain various states of BGP?
What is the reason for an interface stuck on active state?
Do we need to follow 3 way handshake process to establish BGP communication?
What are various path attributes?
What is difference between Local preference and MED attributes?
Explain the sequence of selecting the best route through the attributes?
What is a firewall?
If Firewall is the intermediate device between two OSPF neighbour – what changes need to be implemented in firewall to ensure neighbour ship is built?
If Firewall is the intermediate device between two BGP interface – what changes need to be implemented in firewall to ensure neighbour ship is built?
What piece of information firewall verifies after reassembling the packet?
Explain NAT with respect to firewall?
What is NAT – T, DNAT, SNAT and Static NAT?
NAT-T? Can I Customise NAT-T Port number? NAT-T Types?
Explain Security ZONEs?
Explain DMZ? Why it is required? Benefits of DMZ?
What are Proxy servers & how do they work?
Explain Denial of Service?
Explain some common attacks & how to prevent them?
How does a firewall process a packet?
What are the types of Firewall? Explain.
What is the difference between stateful & stateless?
Explain HA with regards to server clustering?
Explain Active-active and active-passive high availability solutions.
Explain how does standby Know if acive is down.
Explain Failover.
Explain Switchover.
Explain Switchback.
Route based & Policy based
AH,ESP,NAT-T, IKE – V1 & V2, ISAKMP, DH groups, PFS
Phase 1 & Phase 2 (Main, quick & aggressive mode)
Tunnel & Transport Mode
Dynamic VPN
How to troubleshoot IPSEC VPN?
What is the need of Phase 2 negotiation when we already set up communication through Phase 1?
Issue with a particular message of IPSEC VPN?
What is Dynamic IPSEC VPN?
What is the difference between Transport and Tunnel mode?
Explain the traffic flow (for Netscreen)
What are ports used during an IPSec communication phase?
How IPSec works (Phase 1 and Phase 2) ?
What is the difference between IPSec VPN & GRE Tunnel?
Why do we need two phases in IPSec? Can we run IPSec with only one Phase? If Yes, is it Phase 1 or Phase 2 – Justify
What is symmetricAssymmentric  key encryption ?
Explain Hash process.
Explain IKE phases (Main Mode, Aggressive Mode & Quick Mode)
SSL Handshake
Attacks (DOS, TROJAN, WORM, IP Spoofing, Man in the Middle, Session hijack)
Anti Virus
Anti Spam
Content Filter
Web Filter
Mitigation Techniques for the above attacks
Deep packet Inspection
Blocked “at connection level” is when SMTP sender is identified as spam sender based on which parameter?
Anti-virus is responsible for which vulnerability?
Content filtering can permit/deny traffic based on which parameter?
The hacker/untrusted user is trying to change its ip header source as trusted ip header . what type of attack is this?
For the Anti-spam / Anti-Virus / Web-Filtering to work, what are features required on firewall?
How is a VIRUS packet spread across network?
In anti-spam what is the order of verification of email?
What is UTM ?
What is Web application Firewall (WAF)?
Explain Web filtering, content filtering, ANTI SPAM, Anti Virus
Explain deep packet inspection

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