Here is a little guide for subnetting just added by me a few moments ago

thedramathedrama Posts: 291Member
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Ido not have any idea if this short thing will assist you but, i'lltry. Subnetting was my nightmare at the very beginning of my first[/FONT][FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]CCNA[/FONT] [FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]course.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Iwas having hard times by myself but a friend of mine drew myattention to the critical spot/point. After that, it became theeasiest thing for me. [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Now,before subnetting you should know default values of IP subnetclasses. Class A, B and C at first. Why? Because, the 32-bit IPv4address is represented differently on each. [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Imean [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]forclass A, the default illustration if IP address is considered x.x.x.x, is network.host.host.host[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]forclass B , network.network.host.host[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]forclass C, network.network.network.host[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]forexample by default, 10.0.0.0 is one of the IP addresses belongs toclass A. (As you can see above, the first octet is the networkportion)[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]bydefault, 172.16.0.0 is for the class B(As you can see above, 172.16is the network portion)[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]bydefault, 192.168.1.0 is for the class C(As you can see above,192.168.1. is the network portion)[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Whydid i explain this? Because subnetting requires from you to knowthis. [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]I'llgo on soon.[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Howsubnetting is done? By taking host bits from the IP address andreserving them for to describe the subnet address.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Whysubnetting is done? In order to prevent IP addressconsumption.Creating many subnets from a major network. (Once IPv6was not developed)[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Forexample lets assume we have 172.16.0.0/24[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Asyou know, by default, 172.16.0.0 is the class B IP address. So it has255.255.0.0 subnet mask in default. [/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Buthere the CIDR notation is 24, i mean its a distinct value thandefault. What we need to do is substracting first.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]24-16(defaultnotation of class B) = 8. What happened then?[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Ifyou remember the default subnet mask for the class B is 255.255.0.0and it is represented in binary form like[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]below; 11111111.11111111.00000000.00000000[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]then[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]whatwas the illustration for class B ? network.network.host.host[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Weborrowed 8 bits from the third octet(because for the class B, firstand the second octet is reserved for the network) by making allzeroes, 1. So, the result is 255.255.255.0(the previous was255.255.0.0) for the subnet mask[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]inour example 172.16.0.0/24 [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]weneed to do another substraction. 256-255 = 1 (substracted the valuewe obtained from the result from whole) [/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Whatis that "1"? it is the block size which defines that eachsubnet increases by which number. i mean[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]ifthe first subnet is 172.16.0.0, the second will be "here"172.16.1.0 and the other 172.16.2.0 incremented by 1, up to[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]256.. 255 is included. Valid subnets in this example are those.[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Here,the subnet value is calculated as 2^8= 256 valid subnets. Why?Because, we borrowed 8 bits.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Howabout how many hosts are there? to learn this, lets get back toillustration for class B. It was network.network.host.host [/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]but,the result : network.network.network.host(because we had borrowed 8bits from the host portion). Now,[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]howmany host bits remained? 2^8 = 256 bits (bits left other than networkportion after subnetting process) - 2 = 254(i can't remember thereason of this substraction)[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Here,while the first subnet is 172.16.0.0, the first host will be172.16.0.1. The next subnet will be 172.16.1.0 [/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]butthe value before this will be the broadcast address. Thats why, forthe first subnet, the valid hosts[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]usable(can be assigned to the interfaces) are 172.16.0.1 through172.16.0.254(included).[/FONT]


[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Now,VLSM.[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]VLSMis a step further than subnetting to preserve IP addresses. VLSMrefers to variable length subnet mask.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Whatdoes this mean? By default, class A notation is x.0.0.0.0/8 class Bnotation is x.x.0.0/16[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]classC notation is x.x.x.0/24[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]inVLSM you can assign different numbers other than default. Such asx.0.0.0.0/23[/FONT]
Monster PC specs(Packard Bell VR46) : Intel Celeron Dual-Core 1.2 GHz CPU , 4096 MB DDR3 RAM, Intel Media Graphics (R) 4 Family with IntelGMA 4500 M HD graphics. :lol:

5 year-old laptop PC specs(Toshiba Satellite A210) : AMD Athlon 64 x2 1.9 GHz CPU, ATI Radeon X1200 128 MB Video Memory graphics card, 3072 MB 667 Mhz DDR2 RAM. (1 stick 2 gigabytes and 1 stick 1 gigabytes)


Sign In or Register to comment.