Hard Link vs Soft Link

Q.) Soft Link vs Hard Link

Soft Link:

Soft link is the link between files. It is more like shortcut in windows.

You delete a soft link and it does not effect the actual file or directory it is pointing to.

Inode of the linked file is different from inode of the original file.

Deleting original files makes the symlink dangling

Soft Link can link both the files as well as directories and can span across filesystems as well.

Diplayed in Console:
lrwxrwxrwx 12 12 root abc.txt->def.txt

How to create it:

ln -s <Source> <LinkName>

Hard Link:

Both hard link and the actual file share the same inode.

If source file deleted, then hard link still exists.

can not span across different filesystems

Can only link files, not directories.

How to create it:

ln <Source>  <Destination>

What happens when you type www.amazon.com in browser?

1. you type www.amazon.com into the address bar or the browser

2. Your browser checks the cache for a DNS record to find the corresponding ip address.
DNS is a database that maintains a list of website URL and their corresponding ip address it links to.

In order to find the DNS record, the browser checks four caches:

2.1 Browser cache : browser maintains the list of dns records for a fixed duration for websites you have previously visited

2.2 OS Cache: after browser it asks the OS cache for the dns record, by making a call to OS, (gethostname on windows)

2.3 Router cache: browser then communicates with the router to get the dns record

2.4 ISP Cache:

3. ISPs DNS server initiates a DNS query to find the IP address of the server that hosts amazon.com
The purpose of the DNS query is to search multiple DNS server until it finds the correct IP address of the website. This type of search is called recursive search.
 ISPs DNS server is called DNS recursor, whose main job is to find the correct IP address of the URL.
Root Domain = .
Top Level Domain = com, org
second level domain = amazon, google
third level domain = www, download,....

4. Browser initiates a TCP connection with the server
Most common protocol used by browser is TCP. Most of the HTTP connection are made using TCP.
It establishes a three way handshake.

4.1 Client sends a SYN packet to the server over the internet, asking if it is free for connection.

4.2 If the server has open ports that can accept new connection, then it will respond with ACK of the SYN packet, with SYN/ACK

4.3 The client will respond to the SYN/ACK packet by sending a ACK to the server.

Then a TCP connection is established for data transmission.

5. The browser sends an HTTP request to the web server.
The browser now sends a GET or POST request to the webserver, asking for the data or posting the form data respectively.
User-Agent header: info about browser
Accept Header: types of request it will accept
connection: keep the connection alive
Will also pass the cookie information

6. The server handles the request and sends back the response
The server contains a web server, which passes the request to the request handler to generate the response. The request handler is a program which reads the request and generates the response accordingly.

7. The server sends out an HTTP response
The server send out the response, along with status code, compression types (Content-encoding), how to cache the page (Cache-Control).any cookies to set, privacy information, etc.

HTTP Status Codes:

1xx - Informational Message only
2xx - Success messages
3xx - Redirects the client to another URL
4xx - error on the client's part
5xx - error on the server's part

8. Browser displays the HTML content

How do you troubleshoot if you are not able to connect to a database

In Amazon RDS, following could be the reason why you might not be able to connect:

1. Your instance is still booting up and getting ready. It takes about 20 minutes to do so.

2. use the command "netstat -an | grep 3306" on the ec2 instance. if the status is syn_sent, then check for firewall rules on the instance or the security group

2.if you are trying to access rds instance from the internet, then ensure that it is created in public subnet

3. Incorrect authentication. From the instance, try accessing with wrong username and pasword,
it will say access denied for user.

4. DNS is not able to resolve the endpoint: it will say unknown mysql server host
ensure that the endpoint is correct, else check your dns. you can use the tools like nslookup or netconnect, nc.
nc -zv ipaddress port -> name or service not known
you can also use telnet to see if it is listening on that port or not

5. check to see if the rds db instance is healthy
number of connections
amount of cpu used or memory used

How would you ensure High availability of databases

Q.) High availability of databases

High available databases uses an architecture that continues to function normally even when there are hardware or software failures within the system.

They are different from traditional rdbms which are built on single server and are built on master/replica architecture to provide availability.

In the master/replica model, only the master is available for data updates, unless it fails, at which time a new replica takes over as master.

Another approach is that of masterless architecture that uses clustering, where a group of servers get combined, and any server can respond to read or write requests. Data is then replicated across all servers in the cluster, providing system redundancy and minimizing the possibility of downtime.

CAP Theorem: - Dr Eric Brewer
It is impossible for a distributed system to provide simultaneously:
Consistency: multiple values for the same piece of data do not occur

Availability: Operates fully

Partition Tolerant: Responds correctly to node and/or network failure

Configure RDS for high availability
1. Make it multi-AZ
2. failover instance, usually takes 60 - 120 sec.


Q.)How do you ensure uptime of your DB

1. Practise routine maintenance

2. Use management and monitoring tools

3. Make the systems more secure

4. Quality hardware

5. Plan carefully

6. Competent staff

7. Follow change management process

8. Estimating server capacity limits correctly

9. Redundancy of equipments - horizontal scaling

AWS FAQ - Servers and troubleshooting

Q.) Difference between application servers and web servers

Web, application, database server can all run on the same machine or can be distributed across physical machines.



Web server
Server on which your website is hosted. The server will have installed web servers such as apache, IIS.
Deals with HTTP(S) requests. They implement the HTTP specification and know how to handle HTTP request and response object/headers.



Application Server
Server on which your created application which are utilizing your database, web services, etc.
Can also support HTTP requests, but also other protocols, such as RMI/RPC


Other capabilities like load-balancing, clustering, session-failover, connection pooling etc. that used to be in the realm of application servers, are becoming available on web servers as well directly or through some third party products.


Q.) Things to check if your computer is running slow?

1. Too many startup programs

2.Your hard drive is full or nearing an end 
No temp space left.

3. browser has too many add ons

4. Running too many programs at once

5. Your antivirus program could be running scans in the background too frequently

6.Disk Defragmentation
Defragmenting disk minimizes head travel, which reduces the time it takes to read files from and write to the disk.



Q.) Blue screen causes?
Fatal system error
A state where the OS can no longer operate safely
Usually hardware or driver related
Use system restore
Rollback/uninstall device driver
Check that there is enough free space left on the drive where windows is installed
Scan your system for virus
Return BIOS and Hardware Settings to default
Hardware that is not fit properly can also cause sudden death

Q.) Device Manager
Find all your hardware information in one place.
Extention of MS Mgmt Console, that provides a central and organized view of all the MS windows recognized hardware installed in the computer. Like HDD, Keyboard, USB Drive.

It can be used for: 
changing hardware configuration
managing drivers
disabling and enabling hardware

It is like a master list of hardware that windows understand
It is the place where you go if the device is not working correctly.
Such as update a driver, disable the device.
Yellow exclamation point is when windows finds problem with the device.
If a device is disabled it will show red cross or black
It also has error codes if it is having conflict with the system resource

Q.) Virtual Memory
Shortage of RAM is compensated by space in hard disk drive
memory can run out if multiple programs run simultaneously
OS divides the memory into page files or swap files, that contain a fixed number of addresses. Each page is stored on the disk and when that page is needed, the OS copies it from disk to main memory and translates the virtual address into real address.

AWS FAQ - Firewall/ WAF

Q.1) What is a firewall? What is WAF? How is WAF different from iptables? Why might a WAF be a better solution?
Firewall: A software program that prevents unauthorized access to or from a private network. They are a tools that can be used to enhance the security of computers connected to a network.

It is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security tools.

They scan data packets and make sure they don't contain anything malicious.

It can be hardware, software or both.

Packet Filtering Firewall
Only checks the sender and receiver ip address and the port number
Allowed addresses and ports are mentioned in the Access Control Lists.
already implemented in routers
does not check the data portion or the payload

Application/Proxy Firewall
Hides us  from the attacker in internet
does not disclose our ip address
Checks the data packet payload as well. Hence, slower than the packet filtering firewall

Hybrid Firewall
combines packet filtering and application firewall in series

Web Application Firewall
Applies rules to HTTP conversation
allow or deny based on expected input
helps prevents sql injection
It is an appliance or plugin that sits between the organization's network and servers. Directing the access to and from the application and services. It monitors and filters out content that do not meet the advanced criteria of firewall. It is able to specifically montior and filter the contents of specific web application

A regular firewall typically looks at layer 3 and layer 4, such as ip address, port. For HTTP requests, once "allow tcp port 80" is cleared, it is not interested in what is passed through.
A WAF works at layer 7, concerning with security in terms of content of the HTTP request. It prevents attacks like cross site scripting, sql injection.
They shield the web server from the kind of manipulated and malicious requests that attackers use to compromise the web server.


Iptables is an extremely flexible firewall utility for linux operating system
Uses policy chain to allow or block traffic.

When a connection tries to establish itself, the iptables look for a macthing rule, if it doesn't, then it resorts to default action.

Iptables uses three different chains: input, output and forward
Input chain: used to control the behavior of incoming connection
Forward chain: This is used for incoming connections that are not delivered locally. e.g. Router
Output chain: This chain is used for outgoing connection

iptables --policy INPUT/OUTPUT/FORWARD ACCEPT/DROP/REJECT
Accept- allow the connection
drop - drop the connection and dont let receiver know
reject - drop the connection and let the receiver know

iptables -A = append to the rules
it starts from the top of the list and goes till end, until it find a matching rule

example to block all connection from the ip address;
iptables -A input -s 10.10.10.0 -j DROP

block ssh connection from any ipaddress
iptables -A input -p tcp -dport ssh -j drop

Use states when you want to allow two way communication but only one way connection

save the iptables config: sudo service iptables save

list the currently configured iptables rules; iptables -L

to clear all the rules: iptables -f

packet and byte information: iptables -v

Networking 101 - Important concepts....

Topologies:

Layout of how a network communicates with different devices is called a Topology.

Types of Topologies:
1. Star Topology
    All computers are connected to a central point, such as hub or switch. All data passes throught this central point.

Advantage: If a cable or a system in this goes bad, then it wont break the network.
Disadvantage: If central hub or switch fails, then all the computers connected to it, will be effected.

2. Bus Topology:
    In this topology, all devices are connected using single cable, known as backbone.
    Devices are connected using T Connector.

3. Ring Topology
    Each and every device is connected in a closed loop or ring.

4. Mesh Topology
     Every system is connected to every other system.
     Handles failure very well.
 
5. Point to Point Topology
    Two hosts connected to each other.

6. Client Server Topology
    Clients connect to servers to access resources.

7. Peer to Peer
    Every host/system talks to every other client/host with each other.

Firewall

-> can be either software or hardware.
-> Designed to prevent unauthorized access from entering a private network.
->Filters the information that comis in from the internat.
->Blocks unwanted traffic and permits wanted traffic.
-> inspects the data packet and look at their access rules, to allow them to enter the network

-> firewall controls the traffic through it's ACL
ACL are list of rules for what can access the network. Either allows or deny.
Firwalls comes with the rule known as implicit deny.  Thus, it will only allow the traffic which the ACL says to allow.

Host based firewall - software firewall.
Installed on a computer and it protects that computer only.

Network based firewall
combination of hardware and software
operates at network layer
placed between a private network and internet
protects an entire network


Stateful vs Stateless firewall
Firewall inspects traffic in couple of different ways.
Stateful: monitors all the connections and the data streams that are passing through. And keeps a record of it.
It uses the connection information that comes from the application  and previous sessions and factors that in allowing a denying the traffic.
It does a thorough job of protecting the network dynamically.

Stateless: uses an ACL to allow or deny traffic.
     Does not look at the data packet. Only looks at the header portion of it.
     Does not keep a record of previous data packet.

Signature Identification:
Used to detect viruses that have a well known behavior pattern.
Firewalls that use signature identification are programmed to spot these behavior.

IDS/IPS Intrusion Detection/Prevention System
hardware tool that is typically placed between firewall and the internet.
Its job is to alert and prevent a network from outside attack.
such as viruses, malwares and hackers

It monitors traffic flowing through a network looking for suspicious patterns.If it finds any, it alerts the network administrator of the danger.

Network Components

DOCSIS modem: Data over cable service interface specification.
Typical broadband cable modem.
handles both incoming and outgoing data signals including internet video and voice.

HUB
A device that has multiple ports that accepts ethernet connection from network devices.

considered not to be intelligent
It does not filter any data or does not have sense as to which data is to be sent where.

When a data packet arrives at one port, it is copied to all other ports. So all the devices on that hub sees that data packet.

Two types of HUB:
1. Passive hub
    does not require power.
 2. Active hub
     does require power.


Switch
Device that has multiple ports that accepts ethernet connection from network devices.

intelligent - can actually learn physical addresses of the devices that are connected to it.
It stores these addresses in a table.
Thus, if a data packet reaches a switch, it only sends it to the intended device/port. Thus, reducing any unnecessary traffic on the internet.

Regular switches operates at the layer 2 of the OSI model.

Multilayer switch can operate at layer 2 and layer 3 of the OSI model.

interprets layer 3 data similar to router.

Content Switch: operates at L4 - L7 of the OSI model.
can perform load balancing as well as advanced filtering.

PoE - Power Over Ethernet. some devices get their power from the ethernet, instead of a power plug.

Spanning Tree Protocol:
allows for fault tolerance and prevents unnecessary traffic loops in the network.
Allows the switches to talk to each other  to find if loops are happening in the network.


Bridges
Used to divide a network into separate collission domain.
Reduces unnecassary traffic between two segments by filtering the traffic based on their MAC address.

Router
Routes or forwards data from one network to another based on their IP address.
It inspects the data packet to determine the network it is meant for.
Essentially a gateway of the network.

Gateway
A device that joins two networks together.
They interconnect network with incompatible protocols.
It does not change the data, however, it only changes the format of the data.

CSU/DSU - Channel /Data service Unit.
A device which converts data from a LAN to data to a WAN

NIC - network interface card
used to connect a computer to a network.
Each NIC has an associated MAC address.


Wireless Access Point:
Wireless hub that is used by wireless devices. it connects to a wired network and relays data between a wired network and the wireless device for the communication purposes.

Modem: Allows the computer to transmit data over telephone lines. telephone lines carry data in analog, whereas, computer understands digital. Thus, modem converts it.


How to get MAC address in windows computer:
go to CMD
type: ipconfig \all
look for physical address
uniquely identifies each device on a network.
made up of 6 byte hex number


OSI Model
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical


Application Layer
manage communications between applications
supports application protocols such as email, HTTP and FTP
At this layer, data still resembles something that people can read

Presentation Layer
This layer is where data is first converted into a form that can be sent over a network.
data is compressed and decompressed and encrypted or decrypted
sometimes referred to as translation layer

Session Layer
controls the dialog during communications
it establishes, manages and terminates the connections between the local and remote application.

Transport
Provides transfer of data between end users
responsible for resending any packets that do not receive an acknowledgement from the destination
this layer can guarantee that packets are received

Network
responsible for routing the data packet based on its logical IP address
it fragments and reassembles the packets
instructs data on how to find its ultimate destination

Data Link
responsible for sending data to the physical layer
data packets are encoded and decoded into bits
handles flow control and frame synchronization
divided into 2 sub layers, MAC layer and LLC layer

Physical
defines the network standards and physical characteristics of a network. such as connectors, media types, cables, voltages, etc.
defines the topology of the network.



IP Address
A numeric address
identifier for a computer or device on a network

Subnet Mask: it represents how many bits are used for network, in an IP address.



Class A - 1 - 126
Class B - 128 - 191
Class C - 192 - 223
127 is reserved for loopback testing

Private IP:
not publicly registered
can not directly access the internet

Class A - 10.0.0.0 - 10.255.255.255
Class B - 172.16.0.0 - 172.31.255.255
Class C - 192.168.0.0 - 192.168.255.255

Subnetting:
breaking down a large network into smaller networks.
Borrow n number of bits from the host portion.

Formula: 2^n - 2  >= number of subnets you need, where n is the number of bits you need to borrow.

to have 3 subnets, we need to borrow 3 bits from the hosts. as, 2^3 - 2 = 6, and we need 3 subnets only.

hence, the new subnet mask will become: 25.255.224.0


Ip Addresses:

Dynamic IP : it is where a computer gets a dynamic IP from a DHCP server.

DHCP = dynamic host configuration protocol
DHCP works by leasing IP addresses and IP information to network clients for a period of time. For the lease to happen, following is what occurs:

1. the client when boots up, sends out a broadcast packet called DHCPDISCOVER, along with it's name and MAC address.

2. DHCP server responds to the broadcast with the DHCPOFFER packet

3. The client accepts the first offer and sends out a broadcast packet, called DHCPREQUEST

4. The DHCP server whose packet was accepted, responds by DHCPACK message, which acknowledges the lease acceptance and contains the IP address.




It can also assign a subnet mask, default gateway and a DNS server.

Static IP : Assigning the IP address manually.

Self-Assigned or APIPA - Automatic Private IP Address Assignment
In the cases where the computer can not reach a DHCP server for whatever reason, it can provide a private IP address to itself. It is a windows feature and happens only in windows 98 or later.
It's address range is 169.254.0.0.

If the DHCP server later becomes available, then that address is taken.

A DHCP server assigned the IP adresses to the computers from it's scope.

A scope is a group and a range of consecutive IP addresses for computers that gets their IP addresses from a DHCP server.

Setting on Router:
Starting IP address, Ending IP address.

Reservation DHCP
Ensures that a specific computer or device, (identified by its MAC address) will always be given the same IP address when that computer or device accesses the DHCP server.

Reservations are typically given to special devices or computers, such as network printers and servers that require using the same IP address constantly.

Lease DHCP
The DHCP server assigns the IP address  as a lease.

A lease is the amount of time an IP address is assigned to a computer.

on the command prompt type: ipconfig \all
look for "Lease Obtained" and "Lease Expired".

DHCP Relay
If the computer and the DHCP server are on the same subnet, then it is not an issue. It will simply broadcast and DHCP server will assign the IP address.

However, if they are on different subnets, then we have a router in between. It will not allow the broadcast, unless DHCP relay is enabled.
Omce your broadcast reaches the router the DHCP relay will forward it to the DHCP server and the computer will get the IP address.

Transmission Control Protocol:

Connection oriented protocol - it must first acknowledge a session between two computers that are communicating. Which it does using a 3 way handshake.

A -> sends SYN to -> B
B -> sends SYN ACK to -> A
A -> ACK RECEIVED to -> B

Guarantees the delivery of data.

If the data packaet does not go by, then TCP will resend it.


UDP - User Datagram Protocol
Connection less
does not establish a session and does not guarantee delivery
Fire and forget protocol

Due to less overhead of not guaranting delivery, UDP is faster than TCP.

FTP - File Transfer Protocol
Standard protocol used by web users for file transfer
Users can download and upload files through the internet
Connection oriented Protocol, uses TCP for file transfer

TFTP - Trivial FTP
Not used over the internet, instead within the same network.
insecure
uses UDP

SFTP - Secure FTP
Adds a layer of security
Data is encrypted using secure shell during transfer
data is not sent in clear text

SMTP - Simple mail transfer protocol
uses TCP

POP3 - Post Office Protocol v3
used for receiving email
Only downloads the email, does not do any syncing
No copy of the email is remained on the server, unless you tell it to keep a copy.
commonly used with MS Outlook

IMAP4 _ Internet Message Access Protocol
used for receiving Email
Copies of the email are remained on the email server
Syncs email and folders between the mail server and your computer
commonly used with MS Outlook


HTTP - HyperTest Transfer Protocol
used for viewing web pages on the internet
All information is sent in clear text

HTTPS
Secure HTTP
Encrypts the data that is being retrieved by HTTP


Telnet - Terminal Emulation Program
Used to access remote server
Not secure - all commands sent in clear text


SSH - Secure Shell
Acts like a secure tunnel and protects the data from potential threat

ARP - Address Resolution Protocol
Used to resolve IP addresses to MAC addresses
Computers use MAC address for communication
Computers search their ARP cache first to find the targetting MAC address.
If not, it will send the broadcast, asking for which computer has the Ip address, once it does, then it will ask for it's MAC address and the communication will take place.

RARP - Reverse ARP
Just the opposite of ARP
Resolves MAC address to IP addresses


NTP - Network Time Protocol
internet standard for syncing the clocks with the US naval Observatory master clock.

SCP - Secure copy protocol
Uses secure shell to safeguard the data as it's being transferred.


SNMP - Simple Network Management Protocol
used for network management
collects data from various network devices, such as routers, printers and servers

PORTS
categorized by two protocols: TCP and UDP
A logical connection that is used by programs to exchange information
ports are identified by unique numbers
number ranges from 0 to 65535

80 - HTTP
443 - HTTPS
25 - SMTP
20,21 - FTP
22 - SSH
23 - Telnet
53 - DNS
67,68 - DHCP
110 - POP
143 - IMAP
3389 - RDP


DNS - Domain name system
Resolves domain names to IP addresses
works like phone book

NAT - Network Address Translation
Translates a set of IP addresses to another set of IP addresses

e.g. - private to public or public to private

Proxy Server
Caches web pages data accessed, so that next request can be server from there
Benefits: Speed, Bandwidth and security

CSMA/CD - Carrier sense multiple access/ collision detection
used on wired network
if the collision happens then computers will wait a random amount of time before it resends its data.

CSMA/CA - Carrier Sense Multiple Access/Collission Avoidence
Used on wireless networks
computers send small packet before transmitting larger ones.

Broadcast: Single transmitter of data, received by multiple receivers
e.g. wireless router

Unicast: data packets are sent to single destination

Multicast: Sent to multiple destinations at the same time.

Loopback Interface:
A fake or virtual interface that is created on a router
Assigned an IP address of your choice
used for testing and administration purposes

Routing Table
a file that contains set of rules that shows information on what path a data packet takes to its destination.

The router looks at its routing table to find out where to forward the data packet along the best path to it destination

Routing table consists of:
A network destination: the IP address of the final destination
Subnet mask: Determines which part of the IP address is the host and network portion
Gateway: tells the router which IP address the data packet should be forwarded to.
Interface: the outgoing IP address of the device that's sending the data.
Next Hop: The IP address to which the IP address is forwarded to.
Metric: Determines the best route among multiple destinations.

Routing Protocol
collect information about the current network status and map out the best path for data packets to take to their specific destination.

1. Distance Vector : Hops, Distance RIP - Routing information Protocol
Routers that use RIP, broadcast their routing information to other routers every 30 seconds regardless if the routing information has changed or not.

Thus, unnecessary traffic
RIPv2 was created to solve the problem of excess traffic caused by RIP.

BGP - Border Gateway Protocol
standard routing protocol
determines routing directions that are based on paths and policies

Link State Protocol
a routing protocol that is used by routers to share information and independently map out the best path on a network.
e.g. OSPF(Open Shortest path First) - creates a toplogy map of the network
IS-IS - Routers are organized into domain or groups

Hybrid Protocol
EIGRP - Enhanced Interior Gateway Routing Protocol

SIP - Session Initiation Protocol
Establishes communication sessions over internet
e.g. VoIP, Instant Messaging and Conferencing services.

Operates at Application layer of OSI model.

Packet Switching vs Circuit Switching:
PS: the data transferred takes different route for transmission, whereas, in CS, same route is taken.

DSL - Digital subscriber line. Carries voice and data on the same line.
ADSL - download speed is different from upload speed

LAN
Group of computers or servers which are situated in same building or in close proximity to each other.

WAN - Wide Area Netwrok
Network that spans across wide geographical area.

PPTP - Point to Pint Tunneling Protocol
Used for creating VPNs
Ensures data transfer is secure by creating a secure tunnel


VPN - Virtual Private Network
A private communications network that uses a public network to establish a remote connection.

Encrypts data when sending and decrypts data when receiving

provides a dedicated link between two points over the internet.

VPN Concentrator: device used to create VPN connection

VPN - Site to Site: two offices in different Geo region and want to share data over internet
VPN - Host to Site : you are at home and need to connect the office
VPN - Host to Host: connect two devices over internet - no special device needed,SW should do.

Kerberos Authentication:
Authenticates using tickets
A client first authenticates itself by the kerberos server. after which it is given a ticket, which it uses to access network resources.

Cloud Computing:
refers to data and applications being stored and run on a remote servers rather than being on your local computer.

IAAS
infrastructure as a service
3rd party manages the hardware for your business, such as servers, networking and storage
you will have control over the software, such as applications, OS, data

PAAS
Platform as a service
Not only manages the hardware, but also the OS
You are only responsible for the application and the data


SAAS
Software as a service
All the applicationre hosted by 3rd party
no application or data to manage


NAS:
When you want all your data to be stored on a central device connected by a network and can be accessed by other devices on your network.
Will have multiple hard drives in RAID configuration for redundancy

SAN
Storage Area Network
A special, high speed network that stores and provides access to large amounts of data
servers access this data as a local attached hard drive
Not limited or owned by a single server.
Easily expandable and very redundant. All data is shared among several disk arrays.
High speed network

VLAN:
Logically creates several virtual networks to separate network broadcast traffic.

Intranet
private network that belongs to an organization.

QoS
this is a term that is used to provide a guarantee of data delivery within a certain period of time.

Port Blocking
Done on the firewall and as a network administrator, you can control which ports to block.

High Availability
term used to guarantee a period of uptime of continual operation

Server clustering
when a group of servers work together for load balancing and fault tolerance

IPSec:
Internet Protocol security
set of protocol for security which operate at network layer.
encrypts the data when communication is happening between two computers
both sender and receiver must share a public key, which is used to lock and unlock the data as it travels. It prevents data tampering
Transport Mode: Only the message portion is encrypted
Tunnel Mode: entire packet is encrypted

L2TP : Layer 2 Tunneling Protocol
Authenticates both the computer and the user, using a certificate.
prevents man in the middle attack.

SSL - Secure Socket layer
uses public key encryption to secure data
Authenticates the server, the client and it encrypts the data


TLS - transport layer security
Successor to SSL
Made up of 2 layers:
TLS Record protocol:
provides connection security by making sure the connection is private and reliable

TLS handshake protocol:
Allows the server and client to authenticate each other and negotiate an encryption algorithm and cryptographic keys before data is sent.

802.1x
used for wired and wireless networks
controls network access by ports
port based authentication

Router Security:
WEP : Wired Equivalent Privacy
provides security for wireless networks
uses 40 bit encryption keys

WPA - Wifi Protected Access
better than WEP
uses stronger encryption method by using TKIP - Temporal Key Integrity Protocol.- dynamically changes keys as it is being used.Thus, ensures data integrity.


Uses EAP - Extensible Authentication Protocol - which verifies authorized network users


WPA2
stronger than WPA
uses CCMP for encryption

DMZ - Demilitarized zone:
Allows a designated computer to be fully exposed to the internet.
does this by router forwarding all ports to this computer, at the same time.
It is outside the firewall
Typically used for testing purpose
Must(should) be assigned a static IP address

Port Forwarding
forward the request to specific IP address based on the port

Network Utility
Ping: Network connectivity between two devices
can also be used to test name resolution issue. e.g. ping yahoo.com

pathping: shows the details of the path a data packets takes between two devices
combines the functionality of ping and tracert

ARP PING
if you want to check the device connectivity, but are blocked by firewall, then uses ARP Ping.
It only used in LAN and are not blocked by firewalls

Tracert: traceroute
find the exact path the data packet is taking to its destination
tracert <ip address>

ARP - Address Resolution Protocol
resolves IP to MAC addresses.
arp -a -> check arp cache

Netstat utility
displays the current network connections to your computer
netstat -a
also displays which ports are opened and listening for connection

nslookup -> windows, dig->unix
used to lookup dns information
nslookup yahoo.com

Public vs Private IP Address:
A public IP address is the address that can be accessed over the internet. It is a globally unique ip address assigned to a computing device.
Private ip address on the other hand is used to assign computers within your private space without letting them directly expose to the internet.

Internet Assigned Numbers Authority is the organization responsible for registering IP address ranges to organizations and Internet Service Providers (ISPs).

The following IP blocks are reserved for private use:
A - 10.0.0.0 - 10.255.255.255
B - 172.16.0.0 - 172.16.255.255
C - 192.168.0.0 - 192.168.255.255

The devices residing outside of your LAN cannot directly communicate via the private IP addresses, but uses your router's public IP address to communicate. To allow direct access to a local device which is assigned a private ip address, a NAT should be used.



Broadcast Domain:
Broadcast means we send something that everyone receives
Switches will forward the broadcast traffic on all their interfaces except for the one on which they received it.
ARP uses broadcast. it's destination address is 255.255.255.255
Routers unlike switches do not forward broadcast traffic

MTU - Maximum transmission unit - maximum size of single data unit that can be transmissted over a network.


My internet connection speed is slow. How do i troubleshoot?
1. Check your router settings , esp the MTU
2. Avoid wireless signal interference - reposition your router
3. Malware could be the issue as well
4. Stop background program that hog bandwidth
5. Make sure your router and other networking equipment is working
6. call your isp
7. check your speed and your plan
8. run a speedtest on speedtest.net
9. reset your modem and router

Pointer records are used to map a network interface (IP) to a host name. These are primarily used for reverse DNS.

Source:  CompTIA Network+ course on youtube

AWS Cloud Support Engineer/ Solution Architect Frequently Asked Questions

Hi All

Below is the list of commonly asked questions during the interview for the position of AWS solutions architect or Cloud support engineer. ( Source: glassdoor.com)

I signed the non disclosure agreement, and therefore I can't write down all the questions. But know the basics of networking like TCP, UDP, routing protocols, and also how to troubleshoot a network. Know how ping and traceroute work etc. On the behavioral side, just be yourself. Show them that you can handle difficult situations, and give examples. While giving examples, don't say "we did", talk about what "you" did. Use "I" a lot.

Why Amazon

expliain 3 way handshake

Databases Concepts Networking Concepts Amazon Leadership Principles

Name a time you made a decision and the outcome was not what you expected?

Networking, Linux, Leadership principles

Networks and security questions in glassdoor

Lot of troubleshooting questions

HTTP codes.

What is the difference between range and xrange in python.

In what order are group policies applied in Active Directory?

DNS, Basic linux commands, Leadership principles and please go through all the interview questions from glassdoor, they were really helpful.

Explain DNS What is DHCP

how you reach to amazon.com, tell me layer vise. What is DNS? Explain all the steps for DNS. What protocol is used and how it is used to gate out from private network.(ARP)? website is slow how will you troubleshoot ? What is TCP? What is UDP? TCP three way handshake process. Basic l2,l3, some more networking, web servers, windows trouble shooting test, dns server questions. Why Amazon?

Onsite - 2 technical, 2 behavioral rounds. Technical - questions about DNS, DHCP process, TCP/UDP, entire stack and functions of each layer, Active directory, web servers, linux configurations, object oriented programming concepts. Some behavioral skills were also tested by giving some situations. Behavioral - Be ready to tell stories about your past work experience and projects to all the behavioral questions. They write down everything you say so be good at it. Leadership qualities are stressed the most. Handling conflicts, handling failures, misjudgement etc are some of the situations. Think over before you start answering. Also prepare for questions like why do you want to work with amazon? what do you want to do?

If a server failed to do a nightly backup, what could be a reason for that?

TCP/ IP Stack, DNS, DHCP, IP routing, troubleshooting scenarios

Troubleshoot a user's connection problems.

Mostly on my past experience and routing protocol related questions.

Describe in detail how Asymmetric and Symmetric encryption works.

What are the Different DNS Records?

Private IP Ranges

Stage2 - AWS Windows Challenge online: what is Active Directory and why would anyone use it? importance of time in a Windows domain what is sysprep, sysvol, BSoD, DHCP, DNS, DFSR, WINS, Global Catalog, Describe built-in tools to troubleshoot network issues. Some best security practices and a scenario on a company under DoS attack and you choose best answers or suggest any additional answer. Finally, A bonus project to build a system that is robust and fault-tolerance for a start-up ecommerce website. .

Mostly ...tell me about a time when ... Technical questions were - DNS, how to resolve a deadlock, RAID0 and RAID1, linux boot up process etc. Many reviews submitted on this portal very extremely helpful.

Explain the DNS process of getting the IP addresses

1. What happens when you type amazon.com in the browser? ( was asked two times by different interviewers) 2. Phone interview was pleasant and the questions were troubleshooting issues 3. Database administration interview was tough for me. though the questions were simple i was not prepared for a DBA questionnaire. 4. Behavioral questions are pretty straight forward and the interviewers would like to know the experience of you in situations like challenging project/task. be prepared to what you have to answer. 5. Dont leave out to revise on the simple points such as common ports, DBA questions etc. 6. What and how the load value is calculated which is displayed when you give the command "uptime"?

stage 1: Basic Networking questions: What is the difference between Bandwidth, Delay and Latency? What is MTU, Window Size, Segment (MSS)? Describe 3-way handshake. A scenario question about prefix-match and route summarization A scenario question about Stateful/Stateless firewall. A scenario question about packet flow in NAT How DNS work How DHCP work What is BGP and describe the states - Idle, Connect, Active, Opensent, Openconfirm, Established. Tell me a time you went out of your way to do something amazing for a client. Do you have any question for me?

Networking -- covered TCP/ IP , TCP handshake, Layer 3 protocols Linux -- How do you troubleshoot a Server? and other following questions based on that. Linux commands Behavioral : Focus solely on Amazon 14 Principles and relate it to your experience

Hypervisor, VmWare, windows troubleshooting (blue screen of death), DNS, DHCP, what happens when we type www.amazon.com, linux commands (basics since I told Im good in windows), what will you do when you type a website and website isn't coming (how do you troubleshoot?), Active directories in Windows Server, how would you handle a customer who complains that all his data has been lost and no when theres no back up?, difference between cloud and traditional services, what would you improve in AWS? how would you design your web application on AWS? He told next would be onsite if I was selected, but sadly I didnt get selected.

Debugging skills on a webpage nor being found. Linux based rounds where they ask you lot on commands Basic networking stuff with http, dns in particular.

Online Assesement covers IP/TCP, Subneting, Troubleshooting, Private/Public IPs, Routing, Linux Commands like iostat,vmstat, crontab, free, proc/meminfo etc.
Phone Interview: Is 1.1.1.1 routable? What are private IPs ( Ranges)? Are the private IPs submask Classless and Classful? How will you troubleshoot slow website? What linux command to check open ports?  

Most of the questions were based on Linux commands to test the network and IP address range.  

Networking -- covered TCP/ IP , TCP handshake, Layer 3 protocols

Linux -- How do you troubleshoot a Server? and other following questions based on that.
                   Linux commands

About my the best and worse experience.  

They started by asking me a technical project that I have been involved and that I liked, where I described my master thesis, and then there was the technical part.

What is nslookup?
What is fstab?  

what is the difference about UDP and TCP, what kind of application base on UDP
what is FTP? what kind of application it used for?
what the different between HTTP and HTTPS? and why HTTPs more secure?
something related with IP address

what is FTP? what kind of application it used for?
what is the difference about UDP and TCP, what kind of application base on UDP  

• When you type a URL into your web browser, what happens when you press enter?  Answer Question
• A client in Germany is trying to access a server in London, but his connection is running slow. You are in Dublin. How do you diagnose his issue?  Answer Question
• What happens when you press the power button on your PC?  Answer Question
• "I have forgotten my password, how will you help me?"  Answer Question
• How do you find out what your IP Address is?  
• . Cloud v Vitualization 4. How to handle problems like CPU is 100% occupied or the computer is slow what are the possible problems?  
• 1. common ports 2. active directory 3. IPsec 4. DHCP 5. DNS  
• Database :
  
  Knowing the SQL Queries
  Knowing about joins,subqueries,constraints etc.
  Basic database troubleshooting (Like Can’t login, Can’t connect to the database)
  Basic RDMS concept (they can refer tutorial point for the same DBMS topic)
  Networking :
  
  · Difference between router, switch.
  
  · What is a Broadcast Domain?
  
  · DHCP DORA process
  
  · DNS – detailed explanation. TCP/UDP and why?
  
  · Subnetting
  
  · MSS/MTU
  
  · Complete flow when you trigger amazon.com
  
  · OSI model with complete details and protocols on each layer.
  
  · TCP and SSL handshake
  
  · Difference between TCP/UDP, examples
  
  · Flow/error control
  
  · What is a firewall, why do you need it?
  
  · OSI Model
  
  OS :
  
           OS boot process (Win/Linux)
  
  - Memory management ;Memory pages; Buffer and Caches, Basic commands
  __________________
  
  The Aws leadership principles are very important. Every time you answer a question, your way of answering is always evaluated against the 'AWS Leadership Princples'.
  
  3) After clearing the above round you are called at their home location(Indian Candidates) i.e Banglore. Flights and all arrangements are taken care by Amazon. One day Process with 4 rounds.
  
  Rounds include Technical and behavioral analysis. In deep toubleshooting against questions related to the above topics.
  Questions like,
  - My net isn't working, how do i troubleshoot?
  - my net speed is slow, i need you to troubleshoot
  - Whats ptr entry in DNS.
  -Explain DNS, DHCP, Memory management to your grand father.
  -Have you dealt with a bad customer?
  -Any decisions that you regret?
  Etc..
  
  These 4 rounds (technical and behavioral) are one-on-one face-to-face rounds each extending upto 45 minutes to 1 hour.
  
  The answers you give in these 4 rounds are all recorded and evaluated later which decide weather you are selected on not.
• What is Active Directory?
  Difference between static and dynamic routing
  A client in Germany is trying to access a server in London, but his connection is running slow. You are in Dublin. How do you diagnose his issue?  
• 
  

How to setup remote desktop connection using command line in windows 

• 
  
• They wrote in email skills required linux, networks, langauage (java, perl etc) but Technical had questions only from database, o/s, networking and very few linux questions. Overall level was easy but Ikept studying linux and little bit networks. If I knew that o/s was also coming then I would have been able to crack. Still waiting for result. My center was BPIT.HTTP codes 404, 403, 200  Answer Question
• Preemptive Multithreading
• what was the biggest problem faced by you wrt networks  
• 1) Counting the number of trailing zeroes in the factorial of a given number. (number of trailing zeroes means - number of zero's at the end from units place in any number).
  2) A program similar to Fibonacci series.
• The below c code will give u the count of trailing zeros in a factorial of a given number.
  int findTrailingZeros(int n)
  {
      // Initialize result
      int count = 0;
  
      // Keep dividing n by powers of 5 and update count
      for (int i=5; n/i&gt;=1; i *= 5)
            count += n/i;
  
      return count;
  }
• OS concepts like Context Switching, Virtual Memory(Its need), etc.
  DSA questions on functioning of Priority Queues(discussed a lot on this)
  JAVA questions on MultiThreading, Inner Classes and Collections API  
• Writing a SQL query for a particular given table and Normalization of the same
  OS questions on Deadlock and measures to avoid the same
  JAVA questions on polymorphism and edge case outputs in method overloading and overriding
  And a coding question to be solved under the given complexity constraints.  
• Windows OS questions followed by a long discussion about Virtual Memory and its requirement (interviewer got impressed by my knowledge on virtual memory considering I’m from EXTC ), File Mgmt. in windows, Data Structures used in Databases(B-Tree and B+ Trees), Paging concepts in depth in Windows(PAE, PD, PDP).
  JAVA basic concepts in depth (access modifiers, JVM, other modifiers in java, multithreading).
• Virtual memory  Answer Question
• How ip address are allocated  Answer Question
• Difference between tcp and udp  Answer Question
• Osi layers  Answer Question
• Code to check whether a string is pallindrome or not  
• ports used by various protocols
  DHCP
  DNS
  boot loading
  ping and tracerouter mechanism
  slow connection troubleshooting 
• Troubleshooting a slow download issue on PC  Answer Question
• Troubleshooting a PC that doesn't boots up.  Answer Question
• Assigning IP address to PCs.  Answer Question
• How www.amazon.com is accessed, in detail. Explain what happens to packet at each OSI layer.  Answer Question
• TCP/UDP. Why TCP.  
• Basic OS, networking questions were asked along with troubleshooting questions like :
  1. PC is not booting up, what may be the possible reasons?
  2. You are browsing two different things on the same browser how it will be defined which packets of data have to be sent where?
• What is virtual memory?
  Difference between process and thread?
  Difference between buffer and cache?
  Ways to swap without using temporary variable  
• I have a planned incoming DDoS attack against a network, what measures would you put in place to mitigate this? Why would you put these measures in place, what is the benefit vs cost?  
• Better to know some debugging and troubleshooting techniques regarding common pc issues. 

Behavioral: Tell me one time you failed in your professional career.  Answer Question
Public/private ip, static/dynamic ip whar are they, differences.
What happens when you type in browser amazon.com?
Which part is the domain name? Subdomain?
Tcp/udp differences? Use areas?
Http codes?
Dhcp?
Tcp handshake? How to disconnect?

What is a virtual memory?

If someone comes to you with a slow computer what do you do? -check task manager, antivirus, disk fragmentation.
Bluescreen, causes etc.
What is on device manager?

Linux commands: list directory, change directory, check permission?  

• 
  
• How DNS work  Answer Question
• How DHCP work  Answer Question
• Network troubleshooting commands  

I plan to answer all of these and will provide a link to those which are answered already.

Q.1) What is a firewall? What is a WA? How is a WAF different from iptables. Why might a WAF be a better solution than iptables? - Answered

Q.2) Difference between application servers and web servers? - Answered

Q.3) High availability of databases - Answered

Q.4) How do you troubleshoot if you are not able to connect to a database - Answered

Q.5) DHCP DORA process? - Answered

Q.6) What is a Broadcast Domain? - Answered

Troubleshooting. You have a webserver on an ec2 instance. Your instance can get to the internet, but nobody on the internet can get to your webserver. Describe how you would troubleshoot.

What is "big data"? What is a typical big data life cycle? What is map reduce? Describe the steps involved with map reduce. What is HPFS and what advantage does it have for processing big data?

What steps would you perform to enable a server in the private subnet of a VPC to download updates from the internet.

General networking questions. What happens at layer 2? Layer 3? Difference between TCP and UDP. What is MFA?

RAID, Docker, DevOpS, basic networking questions, Design an eCommerce application using AWS services.

Database :

Knowing the SQL Queries
Knowing about joins,subqueries,constraints etc.
Basic database troubleshooting (Like Can’t login, Can’t connect to the database)
Basic RDMS concept (they can refer tutorial point for the same DBMS topic)
Networking :

· Difference between router, switch.





· DNS – detailed explanation. TCP/UDP and why?

· Subnetting

· MSS/MTU

· Complete flow when you trigger amazon.com

· OSI model with complete details and protocols on each layer.

· TCP and SSL handshake

· Difference between TCP/UDP, examples

· Flow/error control

· What is a firewall, why do you need it?

· OSI Model

OS :

         OS boot process (Win/Linux)

- Memory management ;Memory pages; Buffer and Caches, Basic commands
__________________

The Aws leadership principles are very important. Every time you answer a question, your way of answering is always evaluated against the 'AWS Leadership Princples'.

3) After clearing the above round you are called at their home location(Indian Candidates) i.e Banglore. Flights and all arrangements are taken care by Amazon. One day Process with 4 rounds.

Rounds include Technical and behavioral analysis. In deep toubleshooting against questions related to the above topics.
Questions like,
- My net isn't working, how do i troubleshoot?
- my net speed is slow, i need you to troubleshoot
- Whats ptr entry in DNS.
-Explain DNS, DHCP, Memory management to your grand father.
-Have you dealt with a bad customer?
-Any decisions that you regret?
Etc..

These 4 rounds (technical and behavioral) are one-on-one face-to-face rounds each extending upto 45 minutes to 1 hour.

The answers you give in these 4 rounds are all recorded and evaluated later which decide weather you are selected on not.Show Less

Interview Questions

• Database :
  
  Knowing the SQL Queries
  Knowing about joins,subqueries,constraints etc.
  Basic database troubleshooting (Like Can’t login, Can’t connect to the database)
  Basic RDMS concept (they can refer tutorial point for the same DBMS topic)
  Networking :
  
  · Difference between router, switch.
  
  · What is a Broadcast Domain?
  
  · DHCP DORA process
  
  · DNS – detailed explanation. TCP/UDP and why?
  
  · Subnetting
  
  · MSS/MTU
  
  · Complete flow when you trigger amazon.com
  
  · OSI model with complete details and protocols on each layer.
  
  · TCP and SSL handshake
  
  · Difference between TCP/UDP, examples
  
  · Flow/error control
  
  · What is a firewall, why do you need it?
  
  · OSI Model
  
  OS :
  
           OS boot process (Win/Linux)
  
  - Memory management ;Memory pages; Buffer and Caches, Basic commands
  ------------------------------
  
  - My net isn't working, how do i troubleshoot?
  - My net speed is slow, i need you to troubleshoot
  - Whats ptr entry in DNS.
  -Explain DNS, DHCP, Memory management to your grand father.
  -Have you dealt with a bad customer?
  -Any decisions that you regret?

What is Active Directory?
Difference between static and dynamic routing
A client in Germany is trying to access a server in London, but his connection is running slow. You are in Dublin. How do you diagnose his issue?  

How to setup remote desktop connection using command line

  in windows

Preemptive Multithreading

what was the biggest problem faced by you wrt networks  

Major Interview Topics – Networking (CCENT level),
                    Operating System (All of it, but very deep in Memory Management),
                    Coding Questions (DSA in depth)
                    DBMS (Basics of MySQl and DBMS concepts)

Total Interview Rounds -- 1 (Online Technical Coding Test) + 4(3 Technical and One HR)

Total No. Of Students Recruited from VJTI -- 4(2 from EXTC, 2 from COMPS, 1 from IT)

In a gist, if you are in a hurry and want a short description and suggestions, cover all the CCENT exam networking topics for the interview, go deep down in the Memory Management of Operating Systems (It is the most interesting topic in OS) and be flawless in DSA. Also get familiar with Cloud Computing(AWS related and Virtualization Concepts) for advantage.
No round was completely segregated i.e. each round was a mixture of the above mentioned topics.Show Less

Interview Questions

• Questions on TCP handshake and TCP end connection(troubleshooting scenario based)
  Explain DNS short and precisely
  Questions on DNS and ARP(troubleshooting scenario based)  Answer Question
• OS concepts like Context Switching, Virtual Memory(Its need), etc.
  DSA questions on functioning of Priority Queues(discussed a lot on this)
  JAVA questions on MultiThreading, Inner Classes and Collections API  Answer Question
• Writing a SQL query for a particular given table and Normalization of the same
  OS questions on Deadlock and measures to avoid the same
  JAVA questions on polymorphism and edge case outputs in method overloading and overriding
  And a coding question to be solved under the given complexity constraints.  Answer Question
• Windows OS questions followed by a long discussion about Virtual Memory and its requirement (interviewer got impressed by my knowledge on virtual memory considering I’m from EXTC ), File Mgmt. in windows, Data Structures used in Databases(B-Tree and B+ Trees), Paging concepts in depth in Windows(PAE, PD, PDP).
  JAVA basic concepts in depth (access modifiers, JVM, other modifiers in java, multithreading).
  Algorithm Discussion on A*(I’m lucky I knew this), Dijksta, Prim, Kruskal. 

About my the best and worse experience.  

Asking questions such as, what are your strengths, what are your weaknesses. I was also asked to give examples of my communication skills and times when i worked in a team. I was then emailed saying I was shortlisted for a telephone interview.

What is nslookup?
What is fstab?  

what the different between HTTP and HTTPS? and why HTTPs more secure?

give me an example about how did you deal with multiple tasks, how did you handle deadline, how did you deal with angry clients....


A client in Germany is trying to access a server in London, but his connection is running slow. You are in Dublin. How do you diagnose his issue?  

What happens when you press the power button on your PC?  

"I have forgotten my password, how will you help me?"  

How do you find out what your IP Address is?  

• HTTP codes 404, 403, 200  Answer Question
• How DNS work  Answer Question
• How DHCP work  Answer Question
• Network troubleshooting commands  

1. Difference between DNS and IP? 2. Private IP vs Public IP? 3. Cloud v Vitualization 4. How to handle problems like CPU is 100% occupied or the computer is slow what are the possible problems?  

Why amazon?

Tell me about a time when you learned something cool, where you practiced the "Learn and Be Curious" leadership principle.  

Online Assesement covers IP/TCP, Subneting, Troubleshooting, Private/Public IPs, Routing, Linux Commands like iostat,vmstat, crontab, free, proc/meminfo etc.
Phone Interview: Is 1.1.1.1 routable? What are private IPs ( Ranges)? Are the private IPs submask Classless and Classful? How will you troubleshoot slow website? What linux command to check open ports?

know the basics of networking like TCP, UDP, routing protocols, and also how to troubleshoot a network

Know how ping and traceroute work etc.

Hadoop 1.0 & 2.0 architectures and comparisons, Linux commands for troubleshooting.  

What are problems you found with AWS?

What and how the load value is calculated which is displayed when you give the command "uptime"?  

How do you troubleshoot a slow connection

• Troubleshooting a slow download issue on PC  Answer Question
• Troubleshooting a PC that doesn't boots up.  Answer Question
• Assigning IP address to PCs.  Answer Question
• How www.amazon.com is accessed, in detail. Explain what happens to packet at each OSI layer.  Answer Question
• What is virtual memory?
  Difference between process and thread?
  Difference between buffer and cache?
  Ways to swap without using temporary variable  

explain the working of DNS

• 
  
• TCP/UDP. Why TCP.  

Basic OS, networking questions were asked along with troubleshooting questions like :
1. PC is not booting up, what may be the possible reasons?
2. You are browsing two different things on the same browser how it will be defined which packets of data have to be sent where?

I have a planned incoming DDoS attack against a network, what measures would you put in place to mitigate this? Why would you put these measures in place, what is the benefit vs cost?  

"Tell me the most innovative thing you've ever done."

"Tell me a time when <insert Amazon leadership principle here>."

Past job experience. Technical questions. You need to be very clear on what you are doing. You should know your company and competitor's products very well.

2) If you anticipate sudden surge in traffic to your database, what are the steps that you would take?

 Difference between TCP and UDP protocols, how would you design what is needed to host a website on the internet (a VPC and the different components you can use in AWS? Nope. Doesn't apply to this AWS job interview), how would you make switches and routers redundant (because there are switches and routers that you can configure and use in AWS, right?), what would you use to store files on a network (I mentioned AWS EFS but hey, no no... No discussion of AWS features on an interview for an AWS job role) how can you make a fault tolerance database (if you're thinking about automatic snapshots, nope. Read replicas in RDS you say? No AWS topics allowed), what are some of the code repositories available on the internet, what is containerization (don't you dare mention ECS, ECR) why use it instead of a virtual machine, what is the OSI Model, a question about continuous development (can't remember the proper term).

 Recruiter called, ask me some question concerning my background, ask me if I was willing to take a online assessment, there are 4 test to choose, I took the network exam.The next step was a phone interview. He ask question concerning the test you choose, and firewall questions. What is mss, TCP handshake, what type in modes in ipsec, how many host in /27, describe DHCP, how DNS works,what happen…
 when you put www.amazon.com in the browser,when and why did you use wireshark, what's mtu, if you had no connection and thr address of 169.254 what does this means and how to solve the issue.difference between odor and bro, bgp attributes, ospf area, LSA types

 Interview consisted 3 rounds telephonic and onsite interview. They had question on ELB , AS. TCP/IP , UDP. What happens when google.com is typed in the URL. Overall the Interview was on a moderate level . Just make sure you go through your basics well and be prepared on AWS related Question since the job role has so much to deal with AWS related Questions.

Interview Questions

Mainly questions targeted AWS and Network related.

Hard link and Soft link

DHCP, DNS, File systems, Servers, Routing Protocols like EIGRP , OSPF, BGP

Tell me about a time when you made a mistake in your current position.

Tell me about a time when you had opposing views with your manager.

 What's the difference between DNS TCP and UDP


 I can not provided detailed information, but I recommend that focusing on Linux and networking basics, like Linux permission, file hierarchy system, TCP and UDP etc, don't waste your time on programming and scripting, just Linux and networking! And preparing some personal stories which are related with their leadership principles.

 For Big-data: How do you troubleshoot a slow running MR job?

 Have you heard about vm.swappiness kernel parameter? How do you set that parameter?
1 Answer
Do you have any kernel performance, tuning experience?
1 Answer
You need write consistency as well as read Which RAID you would recommend to configure on the storage?
2 Answers
You have been asked as a storage admin How do you benchmarking 2 different storage vendor? 4 TB disk, what are the different benchmarking test that you would do before determine which one best suitable for you?
1 Answer
What is significant of Oracle RAC filesystem compared to traditional ext4 VS, xfs?

Not overly difficult, but the recruiter asked about managing WAN links,

You must prepare well in basics even terms like TCP/IP window size and packet header. Must know Linux scripting, Active directory, LDAP, 'grep' command.

The engineer was very pleasant. He asked about FSMO roles in Active Directory, what are the aspects of setting up a VPN connection between two sites, what all happens when www.amazon.com is typed into a browser, and some basic firewall questions.
On-site, I met with a couple engineers, and several managers. These were a mix of technical questions (describe how you'd set up a network with three locations, what is a GPO and how is it applied in AD, etc) and soft questions (Tell me about a time when doing things the normal way didn't work, Tell me about a time you came up against a problem you'd never seen before, etc).
I thought the process was very thorough, but I never felt like I was being grilled. The people were all great.

IPSEC tunnel/transport mode , main/aggressive mode , BGP MED/LP ,BGP OPEN msg, Website design from network prospective, OSPF neighbor states , port security, linux file system, STP basics

VPN, virtualization
Difference between ospf and BGP

PHONE INTERVIEW
-----------------------
What happens when I type Google into browser,
How does http get request know which domain to go to if a web server is hosting multiple sites,
Can 192.168.1.33/24 talk to 10.0.2.34/24 on the same switch,
What is fstab,
What to do if I couldn't open open a file because it only had rw permissions,
What would be the easiest way to automate a process,
What to do if a website was timing out,
How to know if a service is running on your computer
Customer service related questions
On rhel how to install packages

How do you troubleshoot network issues?

Technical support questions regarding networking/switching, and a strong emphasis on Linux server management/CMD Line (Bash) questions, shell scripting as well.

Last project and how you handle the difficult situation in the project

Tell me about a time when a client was not happy, what happened, and how did you handle that?

If a customer didn't do their back-ups as they were advised and now they've lost all their data, what do you do?

Customer can't ssh into their machine, what do you do?
1 Answer
Tell me about a time you've experienced failure and how you learned from that

What are OSPF neighbor states?

technical round- Encryption. hashing, compromised system, Linux commands, event viewer logs.

What is the most challenging technical hurdle you have overcome in your career? Tell me about your biggest professional mistake? Outside the workplace, how do you sharpen your skill set?

What is AD and why use it
Why is time important in windows domain
What is sysprep
Global catalog
Built in tools to troubleshoot network issues
Best security practices for windows servers
User not authorized to rdp error
Why shouldn’t you reboot during windows updates
What does site binding refer to
How can you list network routes in windows
What shared folder exists on domain controllers and is used to store login scripts
When to implement login script
What does ipconfig result 169.254.2.10
Impact on server system resources
What do you do when your website has been hacked


The interview for Cloud Support Engineer at Amazon started with phone interviews. I went through 3 different interviews, all very technical, with just a few simple personality questions. The technical questions were around subjects related to networking: DNS, BGP, IP, HTTP and other. Questions were not tricky, and if you have general good knowledge of the protocols, then it shouldn't be hard. In my case, my knowledge was not that vast, and I didn't answer a few questions, just told an interviewer that I did not know the answer. Nevertheless, I was invited for additional interviews, and they were also of the same format, and questions were around networking too. After all the phone interviews (I think I had 2 or 3 total), I got an invitation for on-site interview in Texas. At that point, I declined the invitation since I got a different offer. Overall, if you have knowledge, I think interviewing (at least phone interviews) for entry-level positions is not difficult.


Source: glassdoor.com