Help with subnetting
I am currently working from two networking+ books and they differ slightly on subnetting and I was looking for some clarification on the matter.
1) One book states there is 256 hosts available on a class C subnet and the other book states there is 254 hosts, Is this because the the first number is the network identity and the last 255 is a broadcast address which would leave me with 254 hosts?
2)One book states after calculating the network ID to find out the number of hosts available minus the last octet of the subnet mask from the number of hosts available on that class of network ie: A subnet mask of 255. 255. 255. 240 for a class C network I would minus the 240 from 254 leaving us with 14 hosts.
The other book states that after working out the network ID you have 256 hosts for a class C licence.
3)If I was to divide a class C licence into four equal subnets I would be left with four network numbers, four first numbers (router addresses) and four broadcast addresses. Does this mean there is four routers for each of these subnets or does one router do it all and if so how?
Any other help with subnetting would be much appreciated!!!
Thanks
1) One book states there is 256 hosts available on a class C subnet and the other book states there is 254 hosts, Is this because the the first number is the network identity and the last 255 is a broadcast address which would leave me with 254 hosts?
2)One book states after calculating the network ID to find out the number of hosts available minus the last octet of the subnet mask from the number of hosts available on that class of network ie: A subnet mask of 255. 255. 255. 240 for a class C network I would minus the 240 from 254 leaving us with 14 hosts.
The other book states that after working out the network ID you have 256 hosts for a class C licence.
3)If I was to divide a class C licence into four equal subnets I would be left with four network numbers, four first numbers (router addresses) and four broadcast addresses. Does this mean there is four routers for each of these subnets or does one router do it all and if so how?
Any other help with subnetting would be much appreciated!!!
Thanks
Comments
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Webmaster
Admin Posts: 10,292 Admin
1. Yes, that is the reason why there's 254 available for hosts in a C class.
2. Subnetting, as in calculating subnets, is not a simple matter of subtracting. The 240 in 255.255.255.240 means that 4 bits have been taken from the host portion of the IP network address to be used for the network portion of the address (4 bits=128+64+32+16=240), which leaves 4 bits for the host portion, which in turn allows for (2^4)-2 host addresses per subnet, which equals 16-2=14. www.learntosubnet.com is the best place to start if you want to learn more about this.
However, you do not need to know how to calculate subnets for the Network+ exam. You need to know of the classful addresses, and need to know the purpose of subnetting (as mentioned in the exam objectives).
3. Those four networks can be connected to a single router (i.e. to different interfaces) or to multiple routers.
www.techexams.net/technotes/networkplus/networkcomponents.shtml -
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Member Posts: 36 ■■□□□□□□□□
thanks very much I know I don't need to know this for the N+ but I'm hoping to expand past the N+ and thought I'd understand the basics now.
Great site by the way -
Webmaster
Admin Posts: 10,292 Admin
Thanks
Certainly nothing wrong with going beyond the basics, and if you plan to go for any Cisco certs it the subnetting knowledge will certainly be useful.