Monday, October 15, 2012
How To Fix Error 1068
An error occurred while Internet Connection Sharing was being enabled. The dependency service or group failed to start."
Thursday, September 6, 2012
Subnet Mask Information
What is Subnet Mask?
By Scott Seong
By Scott Seong
An IP address has two components, the network address and the host address. A subnet mask separates the IP address into the network and host addresses (<network><host>). Subnetting further divides the host part of an IP address into a subnet and host address (<network><subnet><host>). It is called a subnet mask because it is used to identify network address of an IP address by perfoming bitwise AND operation on the netmask.
A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. Within a given network, two host addresses are reserved for special purpose. The "0" address is assigned a network address and "255" is assigned to a broadcast address, and they cannot be assigned to a host.
Examples of commonly used netmasks for classed networks are 8-bits (Class A), 16-bits (Class B) and 24-bits (Class C), and classless networks are as follows:
| Class | Address | # of Hosts | Netmask (Binary) | Netmask (Decimal) |
| CIDR | /4 | 240,435,456 | 11110000 00000000 00000000 00000000 | 240.0.0.0 |
| CIDR | /5 | 134,217,728 | 11111000 00000000 00000000 00000000 | 248.0.0.0 |
| CIDR | /6 | 67,108,864 | 11111100 00000000 00000000 00000000 | 252.0.0.0 |
| CIDR | /7 | 33,554,432 | 11111110 00000000 00000000 00000000 | 254.0.0.0 |
| A | /8 | 16,777,216 | 11111111 00000000 00000000 00000000 | 255.0.0.0 |
| CIDR | /9 | 8,388,608 | 11111111 10000000 00000000 00000000 | 255.128.0.0 |
| CIDR | /10 | 4,194,304 | 11111111 11000000 00000000 00000000 | 255.192.0.0 |
| CIDR | /11 | 2,097,152 | 11111111 11100000 00000000 00000000 | 255.224.0.0 |
| CIDR | /12 | 1,048,576 | 11111111 11110000 00000000 00000000 | 255.240.0.0 |
| CIDR | /13 | 524,288 | 11111111 11111000 00000000 00000000 | 255.248.0.0 |
| CIDR | /14 | 262,144 | 11111111 11111100 00000000 00000000 | 255.252.0.0 |
| CIDR | /15 | 131,072 | 11111111 11111110 00000000 00000000 | 255.254.0.0 |
| B | /16 | 65,534 | 11111111 11111111 00000000 00000000 | 255.255.0.0 |
| CIDR | /17 | 32,768 | 11111111 11111111 10000000 00000000 | 255.255.128.0 |
| CIDR | /18 | 16,384 | 11111111 11111111 11000000 00000000 | 255.255.192.0 |
| CIDR | /19 | 8,192 | 11111111 11111111 11100000 00000000 | 255.255.224.0 |
| CIDR | /20 | 4,096 | 11111111 11111111 11110000 00000000 | 255.255.240.0 |
| CIDR | /21 | 2,048 | 11111111 11111111 11111000 00000000 | 255.255.248.0 |
| CIDR | /22 | 1,024 | 11111111 11111111 11111100 00000000 | 255.255.252.0 |
| CIDR | /23 | 512 | 11111111 11111111 11111110 00000000 | 255.255.254.0 |
| C | /24 | 256 | 11111111 11111111 11111111 00000000 | 255.255.255.0 |
| CIDR | /25 | 128 | 11111111 11111111 11111111 10000000 | 255.255.255.128 |
| CIDR | /26 | 64 | 11111111 11111111 11111111 11000000 | 255.255.255.192 |
| CIDR | /27 | 32 | 11111111 11111111 11111111 11100000 | 255.255.255.224 |
| CIDR | /28 | 16 | 11111111 11111111 11111111 11110000 | 255.255.255.240 |
| CIDR | /29 | 8 | 11111111 11111111 11111111 11111000 | 255.255.255.248 |
| CIDR | /30 | 4 | 11111111 11111111 11111111 11111100 | 255.255.255.252 |
Subnetting an IP network is to separate a big network into smaller multiple networks for reorganization and security purposes. All nodes (hosts) in a subnetwork see all packets transmitted by any node in a network. Performance of a network is adversely affected under heavy traffic load due to collisions and retransmissions.
Applying a subnet mask to an IP address separates network address from host address. The network bits are represented by the 1's in the mask, and the host bits are represented by 0's. Performing a bitwise logical AND operation on the IP address with the subnet mask produces the network address. For example, applying the Class C subnet mask to our IP address 216.3.128.12 produces the following network address:
IP: 1101 1000 . 0000 0011 . 1000 0000 . 0000 1100 (216.003.128.012)
Mask: 1111 1111 . 1111 1111 . 1111 1111 . 0000 0000 (255.255.255.000)
---------------------------------------------
1101 1000 . 0000 0011 . 1000 0000 . 0000 0000 (216.003.128.000)
Subnetting Network
Here is another scenario where subnetting is needed. Pretend that a web host with a Class C network needs to divide the network so that parts of the network can be leased to its customers. Let's assume that a host has a network address of 216.3.128.0 (as shown in the example above). Let's say that we're going to divide the network into 2 and dedicate the first half to itself, and the other half to its customers.
216 . 3 . 128 . (0000 0000) (1st half assigned to the web host)
216 . 3 . 128 . (1000 0000) (2nd half assigned to the customers)
The web host will have the subnet mask of 216.3.128.128 (/25). Now, we'll further divide the 2nd half into eight block of 16 IP addresses.
216 . 3 . 128 . (1000 0000) Customer 1 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1001 0000) Customer 2 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1010 0000) Customer 3 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1011 0000) Customer 4 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1100 0000) Customer 5 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1101 0000) Customer 6 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1110 0000) Customer 7 -- Gets 16 IPs (14 usable)
216 . 3 . 128 . (1111 0000) Customer 8 -- Gets 16 IPs (14 usable)
-----------------------------
255 . 255 . 255 . (1111 0000) (Subnet mask of 255.255.255.240)
CIDR - Classless Inter Domain Routing
Classless InterDomain Routing (CIDR) was invented to keep the Internet from running out of IP Addresses. The IPv4, a 32-bit, addresses have a limit of 4,294,967,296 (232) unique IP addresses. The classful address scheme (Class A, B and C) of allocating IP addresses in 8-bit increments can be very wasteful. With classful addressing scheme, a minimum number of IP addresses allocated to an organization is 256 (Class C). Giving 256 IP addresses to an organization only requiring 15 IP addresses is wasteful. Also, an organization requiring more than 256 IP addresses (let's say 1,000 IP addresses) is assigned a Class B, which allocates 65,536 IP addresses. Similarly, an organization requiring more than 65,636 (65,634 usable IPs) is assigned a Class A network, which allocates 16,777,216 (16.7 Million) IP addresses. This type of address allocation is very wasteful.
With CIDR, a network of IP addresses is allocated in 1-bit increments as opposed to 8-bits in classful network. The use of a CIDR notated address can easily represent classful addresses (Class A = /8, Class B = /16, and Class C = /24). The number next to the slash (i.e. /8) represents the number of bits assigned to the network address. The example shown above can be illustrated with CIDR as follows:
216.3.128.12, with subnet mask of 255.255.255.128 is written as
216.3.128.12/25
Similarly, the 8 customers with the block of 16 IP addresses can be
written as:
216.3.128.129/28, 216.3.128.130/28, and etc.
With an introduction of CIDR addressing scheme, IP addresses are more efficiently allocated to ISPs and customers; and hence there is less risk of IP addresses running out anytime soon. For detailed specification on CIDR, please review RFC 1519. With introduction of additional gaming, medical, applicance and telecom devices requiring static IP addresses in addition to more than 6.5 billion (July 2006 est.) world population, the IPv4 addresses with CIDR addressing scheme will eventually run out. To solve shortage of IPv4 addresses, the IPv6 (128-bit) address scheme was introduced in 1993.
Wednesday, August 22, 2012
Network engineer Interview Questions & Answere
Questions : 1 What are the two types of transmission technology available?
Answers : (i) Broadcast and (ii) point-to-point
Questions : 2 What is subnet?
Answers : A generic term for section of a large networks usually separated by a bridge or router.
Questions : 3 Difference between the communication and transmission.
Answers : Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc. Communication means the meaning full exchange of information between two communication media.
Questions : 4 What are the possible ways of data exchange?
Answers : (i) Simplex (ii) Half-duplex (iii) Full-duplex. .
Questions : 5 What is SAP?
Answers : Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
Questions : 6 What do you meant by "triple X" in Networks?
Answers : The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
Questions : 7 What is frame relay, in which layer it comes?
Answers : Frame relay is a packet switching technology. It will operate in the data link layer.
Questions : 8 What is terminal emulation, in which layer it comes?
Answers : Telnet is also called as terminal emulation. It belongs to application layer.
Questions : 9 What is Beaconing?
Answers : The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
Questions : 10 What is redirector?
Answers : Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
Questions : 11 What is NETBIOS and NETBEUI?
Answers : NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications. NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
Questions : 12 What is RAID?
Answers : A method for providing fault tolerance by using multiple hard disk drives.
Questions : 13 What is passive topology?
Answers : When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
Questions : 14 What is Brouter?
Answers : Hybrid devices that combine the features of both bridges and routers.
No. minimum spanning tree of a graph give the shortest distance between any 2 specified node Minimal spanning tree assures that the total weight of the tree is kept at its minimum. But it doesn’t mean that the distance between any two nodes involved in the minimum-spanning tree is minimum.
Questions : 15 What is cladding?
Answers : A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
Questions : 16 What is point-to-point protocol ?
Answers : A communications protocol used to connect computers to remote networking services including Internet service providers.
Questions : 17 How Gateway is different from Routers?
Answers : A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
Questions : 18 What is attenuation?
Answers : The degeneration of a signal over distance on a network cable is called attenuation.
Questions : 19 What is MAC address?
Answers : The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
Questions : 20 Difference between bit rate and baud rate.
Answers : Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits. baud rate = bit rate / N where N is no-of-bits represented by each signal shift.
Questions : 21 What are the types of Transmission media?
Answers : Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
a) Guided Media: These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
Thursday, July 26, 2012
General HR Questions
These general questions can be the toughest ones to get through. They might sound easy, but they require a lot of thought and preparation. I would suggest writing down your answers first, then reading them over a few times so that you’re comfortable in answering them.
Some of these questions are very tricky and can get you in trouble.
1. Tell us a little bit about yourself.
2. What are your greatest strengths?
3. What are your greatest weaknesses?
4. What do you like about your current job or what did you like about your last job?
5. Give us an example of when you handled a stressful situation.
6. Give us an example of one of the toughest problems you had to face, and how did you deal with it?
7. Why do you think you should get this position?
8. Do you think you are the best person for this job? If so, why?
9. Why did you apply for this position?
10. Why did you apply for a position with our company and what do you know about us?
11. Why should we hire you?
12. Tell us about your short and long term goals?
13. Where do you see yourself five years from now?
14. Please explain, what does customer service mean to you?
15. What does being a team player mean to you?
16. Give us an example of how you handled a conflict with another employee?
17. What are your salary expectations?
18. What would you consider your most important accomplishment?
19. How would you define success?
20. At your last review, what improvements did your manager suggest you make?
21. What would your coworkers say about you?
System Administration Position
Few more questions that are a little bit more difficult. System Admins should know all these answers by heart in addition to the Network Administrator questions.
1. What is the difference between layer 2 and layer 3 devices?
2. What is the subnet for a class C network?
3. Have you configured a NIS server/client before? If so, describe what you did.
4. Have your configured a NFS server?
5. What are RAID 1 and RAID 5?
6. What are the required components of Windows Server 2003 for installing Exchange 2003?
7. What must be done to an AD forest before Exchange can be deployed?
8. What Exchange process is responsible for communication with AD?
9. What connector type would you use to connect to the Internet, and what are the two methods of sending mail over that connector?
10. How would you optimize Exchange 2003 memory usage on Windows Server 2003 with more than 1Gb of memory?
11. What are the standard port numbers for SMTP, POP3, IMAP4, RPC, LDAP and Global Catalog?
12. Name the process names for the following: System Attendant, Information Store, SMTP/POP/IMAP/OWA.
13. What is the maximum amount of databases that can be hosted on Exchange 2003 Enterprise?
14. What are the disadvantages of circular logging?
15. >What is Active Directory schema?
16. What are the domain functional levels in Windows Server 2003?
17. What is the default domain functional level in Windows Server 2003?
18. What are the forest functional levels in Windows Server 2003?
19. What is a global catalog server?
20. How can we raise domain functional and forest functional levels in Windows Server 2003?
21. What is the default protocol used in directory services?
22. What is IPv6?
23. What are the physical & logical components of ADS?
24. In which domain functional level, we can rename a domain name?
25. What is multimaster replication?
26. What is a site?
27. Which is the command used to remove active directory from a domain controller?
28. What is the file that’s responsible for keeping all Active Directory databases?
Network Administrator Positions
Some of these questions may also be included in the entry level category for Help Desk Technician positions. In either case, they’re worth preparing for.
1. What is the difference between layer 2 and layer 3 in the OSI model?
2. What is the difference between a hub, switch, and router?
3. What is a VLAN?
4. What is the difference between TCP and UDP?
5. How do you distinguish a DNS problem from a network problem?
6. What are a runt, Giant, and collision?
7. What is a broadcast storm?
8. What is the purpose of VRRP?
9. What is a VPN?
10. What is a default route?
11. How do you set a default route on an IOS Cisco router?
12. What is a metric?
13. What is a MAC address?
14. What is ARP/RARP?
15. Describe a TCP connection sequence.
16. What is MTU?
17. What other TCP setting can you modify besides MTU to shorten packets?
Entry level and Help Desk Positions
These question are mostly for help desk positions but i wouldn't be surprised if an entry-level candidate was asked any one of these questions if you don't know the answer, find it, memorize it and then practice explaining it in your own words.
1. What is the difference between a hub and switch?
2. What is a network?
3. What is Active Directory?
4. What is TCP/IP and what does it stand for?
5. What is a default gateway?
6. what does DHCP stand for?
7. What is an IP address?
8. What is the significance of the IP address 255.255.255.255?
9. What are the 3 Major classes of an IP network?
10. What is a class D IP address?
11. What is OSPF?
Subscribe to:
Comments (Atom)