Friday, March 23, 2012

What is a subnet mask?

  • What is a subnet mask?

A subnet mask is used to divide an IP address into two parts. One part identifies the host (computer), the other part identifies the network to which it belongs.
Subnetting an IP network allows a single large network to be broken down into what appear (logically) to be several smaller ones.

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.

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)


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)


http://www.iplocation.net/tools/netmask.php
http://uk.answers.yahoo.com/question/index?qid=20090308095625AALSBe3







  • Subnetting Part 1 IP Basics (Rob Bentz)



-IPV4
-IP address is 32 bits
-IP has 4 octets
-8 bits=1 octet
-IP includes network id and host id information
-network id and host id are specified by subnet mask
-Computers uses boolean AND operation to determine host and network id
-32-bit IP address is converted to 32-bit subnet mask with boolean AND operation
-this conversion with boolean AND operation reveals network id and masks the host id

CIRD tells us how many bits of ip address of subnet mask is on,in other words numerically 1

172.16.1.1/16(CIDR) "/16" means first 16 bits of subnet mask is on
255.255.0.0



  • Subnetting Part 2 The New Mask (Rob Bentz)




  • Subnetting Part 3 Subnets (Rob Bentz)




  • Subnetting Cisco CCNA -Part 1 The Magic Number


How does a router figure out how to route an incoming ip address of a pc with a subnet mask to a network?





  • Subnetting Cisco CCNA -Part 3 The Magic Number




  • Subnetting in 6 easy steps - part 1




  • Subnetting Made Easy Part 2




  • IP Addressing and Subnetting Part 3




  • How to calculate a TCPIP IPv4 subnet mask




  • How to Subnet - HD Tutorial






  • My project needs 6 subnets, but each department has different numbers of host. I have to reserve extra hosts for future growth.

I’m stuck at this part… So what are the IP’s, subnet mask, & network address?
http://webdrift.net/



  • The maximum number of hosts and subnets in a particular subnetwork is designated by a subnet mask.

A subnet mask divides an IP address into the network part and the host part by a number of ones and zeros

So we translate a subnet mask into binary form, or we can use a CIDR mask, and count the number of ones and zeros
(number-of-zeros = 32 - number-of-ones).

The network part of an address is designated by ones in the subnet mask
it means that we can change bits in this part and every time we'll get a different subnet, so the number of combinations in this part is the number of subnets

2 square number-of-ones = number-of-subnets
http://subnet-calculator.samuraj-cz.com/



  • The remaining bits after the subnet are used for addressing hosts within the subnet. In the above example the subnet mask consists of 26 bits, leaving 6 bits for the host identifier. This allows for 64 combinations (26), however the all zeros value and all ones value are reserved for the network ID and broadcast address respectively, leaving 62 addresses.

In general the number of available hosts on a subnet is 2n−2, where n is the number of bits used for the host portion of the address.


  • Rule 1

If the host bits in a given IP address are all set to '0', this is the network or subnet address.
If the host bits in a given IP address are all set to '1', this is the broadcast address (all hosts in the subnet/network are destination).

Rule 2
The formula used to calculate the number of available subnets given the specific length of network mask.

Rule 3
The formula used to calculate the number of available hosts per subnet or network given the specific network mask.

http://ciscoiseasy.blogspot.com/2010/11/lesson-29-ipv4-subnetting-rules.html



  • Subnetting Questions with Detailed Answers:


 1. You work for a large communications corporation named GlobeComm which has been assigned a Class A network address. Currently, the company has 1,000 subnets in offices around the world. You want to add 100 new subnets over the next three years, and you want to allow for the largest possible number of host addresses per subnet.
http://academic.keystone.edu/cisco/documents/subnetting/SubnettingQuestionsAndAnswers.htm
Your router has the following IP address on Ethernet0: 172.16.2.1/23. Which of the following can be valid host IDs on the LAN interface attached to the router?

 172.16.1.100
172.16.1.198
172.16.2.255
172.16.3.0

 http://www.indiabix.com/networking/subnetting/
Solving Subnetting Questions for the Cisco CCNA - 1
What is the subnet? Easy Solution
Subnet a Network in Packet Tracer - Part1
Configure Devices in Packet Tracer - Part2
Configure Static Routes in Packet Tracer - Part3
  • Subnet Calculator is used to divide an IP network into subnetworks by calculating network address, subnet mask, broadcast address and host IP address range 
Subnet Calculator (IPv4 Only)
IP Subnet Calculator
Subnet Calculator
Subnet Calculator
Subnet Calculator
Subnet Calculator
IP Subnet Calculator
Subnet Calculator
IP Subnet Calculator
Subnetting Mastery - What is Subnetting? - Part 1 of 7

  • What are the benefits of subnetting?
Subnetting helps reduce network traffic and the size of the routing tables. It’s also a way to add security to network traffic by isolating it from the rest of the network

http://www.enterprisenetworkingplanet.com/netsysm/10-killer-interview-questions-for-network-professionals.html


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1 comment:

  1. DavidJune 13, 2020 at 1:56 PM

    For the Subnet Calculator, there is another great tool
    Subnet Calculator (IPv4 Only)
    you must check it out as well.

    ReplyDelete