Can't understand sub-net masking in IP, NE1 make it REAL EZ?

Question

Seems like a needless redundancy of the IP address, but the documentation stresses its importance. Since I am not a math whiz, can anyone explain the purpose of subnet, please without the binary stuff. I got like a 63 in math about fifty years ago.

Answer 1

The subnet mask tells the computer that the IP address pool is comprised of a certain number of "networks" and a certain number of "hosts" (computers). If there were no subnet masks, then there would only be a limited number of combinations out of which to assign IP addresses. Everything would be in one big network. I think Andy T's explanation is great. If you thought of the school building as the network, and each class as a sub-net (network), then the gateway would be the door to each classroom. If a packet wasn't in your classroom, it would be sent out into the hallway to go see it's DNS in the office in order to locate what classroom it was supposed to go to.

Answer 2

the answer is in binary... not really math.

all ipv4 addresses are 4 bytes long, a byte is 0-256

usually you break it into 3 parts, the net , the subnet, and the host.
there are 3 major ways to break it down
class a: 1 byte for the net
class b: 2 bytes for the net
and
class c: 3 bytes for the net

the left over is for the host

the subnet is carved out of the net, if it is used, it's really for the routers only.

of course you can change the lengths, but don't!

certain addresses are expected to be a particular class
a 1-63
b 65-126
c 128-256 (actually less , because there is a little reserved for class d and e)

by modifying the normal rules you can change these rules, and that is often called subnetting.

Hope it helps!

Answer 3

The practical reason is that it tells the computer whether a particular IP address (that an application on the computer may want to talk to) is on the local Ethernet or not. If it is, the computer tries to find the Ethernet address of that other computer (which it can do only if the other computer is actually on the local Ethernet) and then it sends the data directly to that Ethernet address. If not, it sends the data to a router and lets the router figure out how to send the data onward. The computer knows the IP address of the router because that is the "gateway address" that you either enter by hand or get from a DHCP server. Notice that the router's IP address MUST be on the local Ethernet (or you'd need another router to reach the router).

Answer 4

It is very important, without it everyone would be in one large unsegmented network. Since you brought up school classes let's use that as analogy: if the school didn't assign and segment the large pool of students then 1 grade year would constitute one large class and it'll be hell for the teacher to manage that one huge class, so schools took the time and procedure to segment pupils into classes of around 20-30 (or any manageable size); in the same way subnet mask is that procedure.

Because the necessity of it in larger networks, this subnet mask became part of the standard even for networks of very small size.

Because of using subnet masks even in situations like a small network, you can easily slave in networks as one machine entity to a larger network, hence the word "Internet"

Answer 5

OK, subnet masking is used to group ip addresses together. The larger the subnet mask, the smaller the group of addresses. So 255.255.255.255 is the largest possible subnet mask, so it is used to define a single ip address. 255.255.255.254 would designate a group of 2 ip addresses. 255.255.255.252 would designate a group of 4 addresses. .248 a group of 8 addresses, 240 a group of 16 addresses etc etc.

Answer 6

While I understand that they are real people in this forum. It must be realized this is just a forum...it shouldn't make or break anyone. Anonymity seems to give people (atheist, Christians, everyone) the idea that they can say any flippant thing they want to (sort of like driving a car makes some people very aggressive). To me, I know this, so it doesn't even come close to bothering me. I take the occasional valuable insight, and I ignore all the rest.