Author Archives: Jugal Shah

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About Jugal Shah

Jugal Shah has 19 plus years of experience in leading and managing the data and analytics practices. He has done the significant work in databases, analytics and generative AI projects. You can check his profile on http://sqldbpool.com/certificationawards/ URL.

Networking Questions

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What is DNS?

Domain name system/server is used to translate the IP address into the hostname and hostname into the IP address. DNS is mostly used on the internet and the networks.

What is DHCP?

Dynamic host configuration protocol is used to dynamically assign the IP address to the networked computers and devices. DHCP is a network protocol that automatically assigns static and dynamic IP addresses from its own range.

What is a Router?

Router is the most important network device that is used to connect two logically and physically different networks. Router defines the short possible route for the data to reach its destination. A router works with built-in intelligent software known as routing table, which helps to determine the route between the two networks.

What is Gateway?

A gateway is software or a hardware that is used to connect the local area network with the internet. A gateway is a network entrance point and a router usually works as a gateway.

What is WLAN?

WLAN or Wireless local area network is simply a type of network that doesn’t use wired Ethernet connections for networking. WLAN uses wireless network devices such as wireless routers etc.

What is Subnet Mask?

A subnet mask is used to determine the number of networks and the number of host computers. Every class of the IP address uses the different range of the subnet mask. Subnet masks allow the IP based networks to be divided into the sub networks for performance and security purposes.

What is a MAC Address?

MAC address or Media Access control is a unique identifier of a computer device. The MAC address is provided by the manufacturer of the device. MAC addresses are 12 digital hexadecimal numbers.

What is an IP Address?

An IP address is a unique identifier of a computer or network device on the local area network, WAN or on internet. Every host computer on the internet must have a unique IP address. IP addresses on the internet are usually assigned by the local ISPs to which users are connected.

What is Wifi?

Wi Fi or wireless fidelity is a base band network technology that is used for the wireless data communication.

What is WiMax?

Wi Fi is a next form of the Wi fi. Wi max is a very high speed broadband network technology that is designed for the corporate offices, roaming and home users.

Name the Seven Layers of OSI Model

The seven layers of the OSI are Application, Presentation, Sessions, Transport, Network, Data Link and Physical layer.

What is LDAP?

Lightweight Directory Access Protocol is used to access the directory services from the Active directory in Windows operation systems.

What are the standard port numbers for SMTP, POP3, IMAP4, RPC, LDAP, and FTP?

SMTP – 25, POP3 – 110, IMAP4 – 143, RPC – 135, LDAP, FTP-21, HTTP-80

What is IPv6?

IP V6 is a next generation protocol that is used as an expansion of DNS.

What is UDP?

UDP or user datagram protocol is a connectionless protocol that is used to transfer the data without any error handling.

What is Firewall?

A firewall is usually a software program that is installed on the network server or gateway. The purpose of the firewall is to protect the network resources from the intruders and unauthorized persons.

What is Virtual Private Network (VPN) and how does it work?

VPN or virtual private network is used to connect two networks by means internet. VPN uses PPTP (point to point tunneling protocol) and other security procedures to make a secure tunnel on internet.

Define VOIP

VOIP or voice over internet protocol is a technology that uses IP based networks such as internet or private networks to transmit the voice communication.

Define Bluetooth Technology

Bluetooth is a short range wireless technology that uses radio waves for communication. Many mobile phones, laptops, MP3 players have built in features of the Bluetooth.

What is a RAS server?

RAS or remote access server allows you to remote dial in through the desktop computers, laptops and GSM mobile phones.

What’s a Frame Relay?

Frame relay is high speed data communication technology that operates at the physical and data link layers of the OSI model. Frame relay uses frames for data transmission in a network.

Networking Interview Questions

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What is IPv6?

Internet Protocol version 6 (IPv6) is a network layer IP standard used by electronic devices to exchange data across a packet-switched internetwork. It follows IPv4 as the second version of the Internet Protocol to be formally adopted for general use.  ipv6 it is a 128 bit size address. This is total 8 octants each octant size is 16 bits separated with “:”, it is in hexa decimal format. These 3 types:

  1. unicast address
  2. multicast address
  3. anycast address

loopback address of ip v6 is ::1

What is subnet?

A subnet allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance.

What is Subnet Mask?

A mask used to determine what subnet an IP address belongs to. An IP address has two components, the network address and the host address. For example, consider the IP address 150.215.017.009. Assuming this is part of a Class B network, the first two numbers (150.215) represent the Class B network address, and the second two numbers (017.009) identify a particular host on this network.

Subnetting enables the network administrator to further divide the host part of the address into two or more subnets. In this case, a part of the host address is reserved to identify the particular subnet. This is easier to see if we show the IP address in binary format.

What is Default Gateway?

a gateway is a device on a network that acts as an entrance to another network. In more technical terms, a gateway is a routing device that knows how to pass traffic between different subnets and networks. A computer will know some routes (a route is the address of each node a packet must go through on the Internet to reach a specific destination), but not the routes to every address on the Internet. It won’t even know all the routes on the nearest subnets. A gateway will not have this information either, but will at least know the addresses of other gateways it can hand the traffic off to. Your default gateway is on the same subnet as your computer, and is the gateway your computer relies on when it doesn’t know how to route traffic.

The default gateway is typically very similar to your IP address, in that many of the numbers may be the same. However, the default gateway is not your IP address.

Describe how the DHCP lease is obtained.
It’s a four-step process consisting of (a) IP request, (b) IP offer, © IP selection and (d) acknowledgement.

What’s the difference between forward lookup and reverse lookup in DNS?
Forward lookup is name-to-address, the reverse lookup is address-to-name.

How can you recover a file encrypted using EFS? Use the domain recovery agent.

What is LMHOSTS file?
It’s a file stored on a host machine that is used to resolve NetBIOS to specific IP addresses.

How can you force the client to give up the dhcp lease if you have access to the client PC?
ipconfig /release

Open Systems Interconnection Model

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OSI 7 Layers Reference Model For Network Communication

Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary architectural model for inter-computing and internetworking communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, which divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.

The OSI 7 layers model has clear characteristics. Layers 7 through 4 deals with end to end communications between data source and destinations. Layers 3 to 1 deal with communications between network devices.

The specific description for each layer is as follows:

Layer 7:Application Layer

Defines interface to user processes for communication and data transfer in network

Provides standardized services such as virtual terminal, file and job transfer and operations

Layer 6:Presentation Layer

Masks the differences of data formats between dissimilar systems

Specifies architecture-independent data transfer format

Encodes and decodes data; Encrypts and decrypts data; Compresses and decompresses data

Layer 5:Session Layer

Manages user sessions and dialogues

Controls establishment and termination of logic links between users

Reports upper layer errors

Layer 4:Transport Layer

Manages end-to-end message delivery in network

Provides reliable and sequential packet delivery through error recovery and flow control mechanisms

Provides connectionless oriented packet delivery

Layer 3:Network Layer

Determines how data are transferred between network devices

Routes packets according to unique network device addresses

Provides flow and congestion control to prevent network resource depletion

Layer 2:Data Link Layer

Defines procedures for operating the communication links

Frames packets

Detects and corrects packets transmit errors

Layer 1:Physical Layer

Defines physical means of sending data over network devices

Interfaces between network medium and devices

Defines optical, electrical and mechanical characteristics

What is the Global.asax file?

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What is the Global.asax file?

The Global.asax file (also known as the ASP.NET application file) is an optional file that is located in the application’s root directory and is the ASP.NET counterpart of the Global.asa of ASP. This file exposes the application and session level events in ASP.NET and provides a gateway to all the application and the session level events in ASP.NET. This file can be used to implement the important application and session level events such as Application_Start, Application_End, Session_Start, Session_End, etc. This article provides an overview of the Global.asax file, the events stored in this file and how we can perform application wide tasks with the help of this file.

According to MSDN, “The Global.asax file, also known as the ASP.NET application file, is an optional file that contains code for responding to application-level events raised by ASP.NET.” The Global.asax file is parsed and dynamically compiled by ASP.NET into a .NET Framework class the first time any resource or URL within its application namespace is activated or requested. Whenever the application is requested for the first time, the Global.asax file is parsed and compiled to a class that extends the HttpApplication class. When the Global.asax file changes, the framework reboots the application and the Application_OnStart event is fired once again when the next request comes in. Note that the Global.asax file does not need recompilation if no changes have been made to it. There can be only one Global.asax file per application and it should be located in the application’s root directory only.

The following are some of the important events in the Global.asax file.

· Application_Init

· Application_Start

· Session_Start

· Application_BeginRequest

· Application_EndRequest

· Application_AuthenticateRequest

· Application_Error

· Session_End

· Application_End

The purpose of these event handlers is discussed in this section below.

Application_Init

The Application_Init event is fired when an application initializes the first time.

Application_Start

The Application_Start event is fired the first time when an application starts.

Session_Start

The Session_Start event is fired the first time when a user’s session is started. This typically contains for session initialization logic code.

Application_BeginRequest

The Application_BeginRequest event is fired each time a new request comes in.

Application_EndRequest

The Application_EndRequest event is fired when the application terminates.

Application_AuthenticateRequest

The Application_AuthenticateRequest event indicates that a request is ready to be authenticated. If you are using Forms Authentication, this event can be used to check for the user’s roles and rights.

Application_Error

The Application_Error event is fired when an unhandled error occurs within the application.

Session_End

The Session_End Event is fired whenever a single user Session ends or times out.

Application_End

The Application_End event is last event of its kind that is fired when the application ends or times out. It typically contains application cleanup logic.

“Cannot Generate SSPI Context” error message, more comments for SQL Server

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The Cannot generate SSPI context issue is described by http://support.microsoft.com/?id=811889 in general. In this article we will discuss one daunting case of “Cannot generate SSPI context” error message when failing to connect to SQL server.

In most related cases, customers report this issue as “They are not able to connect to their local SQL Server, but once they connect to my network, they can’t connection to my local SQL Server”.

Such issue is reported against MSDE and SQLExpress versions. But actually, it can happen with any version/edition of SQL Server, including SQL Server 2000 and SQL Server 2005 that support NT integrated authentication.

The error message for the failed connection is
[SNAC] “[SQL Native Client]SQL Network Interfaces: The Local Security Authority cannot be contacted.[SQL Native Client]Cannot generate SSPI context”

[MDAC] “Cannot generate SSPI context”;

Failed System.Data.SqlClient.SqlException: Cannot generate SSPI context

It can happen when all of followings are true:
(1) The hosting machine of SQL Server is connected to a network, including home network or dialup connection, but it is disconnected from its domain.
(2) The OS of the hosting machine is Windows XP or 2000. Not windows 2003.
(3) The connection is to a local SQL Server.
(4) Connection configuration causes network library to choose TCP/IP provider.

A scenario that meets all of (1) (2) and (3) looks like an extreme corner case. But the reality is that it is quite often if the hosting machine is a laptop computer.

To avoid condition (1) by connecting to your corporate domain through VPN or disconnecting from network completely.

From user’s perspective, however, in many cases, either connecting over VPN or disconnecting from network might prevent you from accessing some valuable resources, so I want to discuss solutions that do not depend on (1) first.

In most cases, users do not explicitly require TCP/IP as the connection provider. For example connection strings in form of “.\”, “(local)\”, “\” are among them. We might wonder why network library chooses TCP/IP provider instead of Shared Memory provider, if the connection string is not prefixed with “tcp” and the server is local.

Answer is that it can happen if the TCP/IP provider is in front of other providers in the client protocol order list, or/and the local server is not listening on Share Memory and Name Pipe.

As described above, only TCP/IP provider has the issue; hence, configuring network library not to choose TCP/IP is a solution. To do that, first, on the server side, make sure your server is listening on Shared Memory or/and Named Pipe connection requests; then, on the client side, change the protocol order list such that Shared Memory and/or Named Pipe are in front of TCP/IP, or prefixing your connection strings with “lpc” or “np” to force Shared Memory or Named Pipe, or using alias that prefix Named Pipe in connection strings, whichever you feel most comfortable with. Note that certain SKUs of SQL Server have named pipe connection turned off by default.

If You really want the TCP/IP connection, the option is to use TCP/IP loop-back address, i.e. “127.0.0.1”, as your . You can also add an entry into the /etc/host file as well.

For example, if your connection string has form of “\” and is not prefixed with “tcp”, without modifying the connection string, you can configure an alias with alias name as \, protocol as TCP/IP, server as “127.0.0.1\” or “127.0.0.1,”.

Remember that the “Cannot Generate SSPI context” problem described in this post only happens when connecting to a local server; thus, the “127.0.0.1” is applicable.

Be aware that only TCP/IP provider can provides the benefits of Kerberos authentication as discussed in http://blogs.msdn.com/sql_protocols/archive/2005/10/12/479871.aspx

From the error message reported by SNAC ODBC/OLEDB, you can differentiated the issue described by this post from another case of “Cannot generate SSPI context”, in which the root cause is because, in Active Directory, the Service Principle Name (SPN) of SQL Server is registered for a domain account different from the SQL Server is actually running under.

Make sure service account has enough permission in AD to register the SPN. You can check the below parameters for SPN as well.

SET SPN-L Service Account. You can get more information for the SPN from this post.
http://sqldbpool.com/2009/11/26/service-principle-name/

Check that SPN is registered, if registered there shouldn’t be duplicate entry, should be match with the service account, Service account should have enough permission, PORT number is correct.

For the connection failure…
You can also check Resolving Connection failure article.