Process to remove subscription from your RedHAt linux end configure yum manually

What command will remove subscription from your RedHAt linux server? 

#  yum remove subscription-manager yum-rhn-plugin 

Hit yes :- ) 

What do you understand by ARP and RARP ?

Difference between ARP and RARP:- 

ARP : Address Resolution Protocol is utilized for mapping IP network address to the hardware address that uses data link protocol.

So,IP address of destination to physical address conversion is done by ARP, by broadcasting in LAN.

RARP : Reverse Address Resolution Protocol is a protocol using which a physical machine in a LAN could request to find its IP address from ARP table or cache from a gateway server.

And , Physical address of source to IP address conversion is done by RARP. 

ARP associates 32 bit IP address with 48 bit physical address.Allowing a host to discover its internet address after knowing only its physical address is done by RARP.

Explicit proxy mode

Explicit proxy mode 

Use this information to better understand explicit proxy mode on your Gateway appliances.In explicit proxy mode, some network devices must be set up explicitly to send traffic to the device.The device then works as a proxy or relay, processing traffic on behalf of the devices.

Explicit proxy mode is best suited to networks where client devices connect to the device through a single upstream and downstream device.

Here , In this figure firewall and Gateway appliance are connect to a switch.

OSI Models

1. Physical Layer: 

Basically in this layer information gets from your computer is converted to digital signal ; information taken from strings and convert it to binary and transfer it into the lan. Basically you are transmitting 1 bit or multiple bit at a time. that is what physical layer is responsible for .

2.  Data Link Layer : 

• This is where NIC card just switch to NIC card(Just end to end)
• Frame error checking 
• Responsible for Information you are trying to send is going into correct order. 
• Frame acknowledgement 
• Here , CSMA/CD - Carrier Sense Multiple Access / Collision Detection means if it detects collision they basically listen to the line for certain amount of time and when they are free they start transmission again .  

3. Network Layer : - 

• Logical to physical 
• Traffic control 

4.Transport Layer : -

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
- Layer 4 Transport examples include SPX, TCP, UDP.

5. Session Layer :- 

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

- Layer 5 Session examples include NFS, NetBios names, RPC, SQL.

6. Presentation Layer :- 

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

- Layer 6 Presentation examples include encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI.

7. Application Layer :- 

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

- Layer 7 Application examples include WWW browsers, NFS, SNMP, Telnet, HTTP, FTP

Fig:OSI Models 

Networking Basics: The Difference Between Hubs, Switches and Routers

The Difference Between Hubs, Switches and Routers : -

Hubs : 

• Legacy , rarely seen , useful for comparison 
• Single broadcast domain 
• Single collision domain 

A hub is typically the least expensive, least intelligent, and least complicated of the three. Its job is very simple – anything that comes in one port is sent out to the others.

Switches : - 

• It also Single broadcast domain but has collision domains but still can see the broadcast domain 
• Layer 2 device 

In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs

Routers/Layer 3 Switches :- 

• Interchangeable term 
• Many broadcast domains 
• Many collision domains (collision are limited to one particular host) 
• Layer 3 device (router), Layer 2/3 (L3 switches) because many Cisco Switches are Layer 3 capable  

Router forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP.s network. Routers are located at gateways, the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

Log in failed to RHEL Server using PUTTY : shows "Access denied"

If you want want to log into RHEL using PUTTY and it shows "Access denied" , How to fix this ?


Follow Simple Troubleshooting Steps : -

1. # First ping x.x.x.x from the machine. 

2. Then log in to RHEL using root user.
then use following command
3. # vim /etc/ssh/sshd_config


sshd_config -- OpenSSH SSH daemon configuration file

find (/GSSAPIAuthentication) press i to edit and then 

then >> set GSSAPIAuthentication No
if GSSAPIAuthentication yes then it will not allow you to login to your RHEL server. 

then finally restart sshd. 

4.
# /etc/init.d/sshd restart or 
# service sshd restart


if  you are still facing problem ... then check allow users and root are permits .
Also check .. 

PermitRootLogin yes

AllowUsers admin admin2 user2 user1

What is Data deduplication ?

What is Data deduplication ?

Data deduplication is a technique for reducing the amount of storage space an organization needs to save its data.

In its simplest form, deduplication takes place on the file level; that is, it eliminates duplicate copies of the same file.

This kind of deduplication is sometimes called file-level deduplication or single instance storage (SIS). Deduplication can also take place on the block level, eliminating duplicated blocks of data that occur in non-identical files. Block-level deduplication frees up more space than SIS, and a particular type known as variable block or variable length deduplication has become very popular.

Often the phrase "data deduplication" is used as a synonym for block-level or variable length deduplication.

Why Gartner

Why Gartner

Gartner is the world's leading information technology research and advisory company. We deliver the technology-related insight necessary for our clients to make the right decisions, every day.

• Unparalleled expertise across our wide range of solutions.
• More than 960 expert analysts cover 1,200 topics across the IT landscape
• Gartner analysts are based in 26 countries and speak 47 languages
• Gartner analysts have an average of 12 years experience in their specific field

• Gartner insights are drawn from a critical fact
  base not available anywhere else.
• Each year Gartner manages:
• Interactions with clients in 14,000 distinct organizations world-wide
• 200,000 one-on-one client interactions
• Our rigorous research process and proven methodologies provide the foundation for unbiased, pragmatic and actionable insight.
• Gartner can be the difference between success and failure in the outcome of your critical IT initiatives
• Gartner can help you save thousands or millions of dollars on purchase decisions and operating budgets
• Gartner is the key to your success in IT
• 18,500 vendor briefings 

POP3 vs. IMAP

POP3: All emails are to be downloaded again if used by another desktop PC for checking the email.May leads to confusion if used for checking email in office and at home pc.Attachments will be down loaded into desktop while the ‘check new email’ process is in progress.Mailboxes can be created only on desktop and one mail box exists on the server.



IMAP: There is no need for downloading all email while using another desktop PC for checking email.Unread mail identification is easier. Message downloading is possible only when opened for display from its contents. Multiple mailboxes creation is possible on the desktop PC and also on the server.

VPN

VPN is a service that offers secure, reliable connectivity over a shared public network infrastructure such as the Internet. VPNs maintain the same security and management policies as a private network. They are the most cost effective method of establishing a virtual point-to-point connection between remote users and an enterprise customer's network.

Consumers use a private VPN service, also known as a VPN tunnel, to protect their online activity and identity. By using an anonymous VPN service, a user's Internet traffic and data remain encrypted, which prevents eavesdroppers from sniffing Internet activity. A VPN service is especially useful when accessing public Wi-Fi hotspots because the public wireless services might not be secure. In addition to public Wi-Fi security, a private VPN service also provides consumers with uncensored Internet access and can help prevent data theft and unblock websites.

It is a network that used the public telecommunication infrastructure. This means that it used public wires to connect the nodes. E.g. Internet. VPN supports remote access to computers and allow data to be transmitted over this public network. Even though the data is transmitted over a public network, encryption and decrypting data to ensure security.