subnet masking

[doffins]

Do the octets in a subnet mask have to be 255? Can it be, for example, 252? I thought they were always 255.

"If you have cable, open your PC's command prompt, type ipconfig, and check out your subnet mask. It's probably a /20 or /21 Class B address—yikes! You already know that translates to either 4,094 or 2,046 hosts per cable network connection. Definitely not good."
Lammle, Todd (2012-01-09). CompTIA Network+ Study Guide: Exam N10-005 (p. 502). John Wiley and Sons. Kindle Edition.
Concerning the above statement, how would you know how many hosts there are?

 

[kmote]

Do the octets in a subnet mask have to be 255? Can it be, for example, 252? I thought they were always 255.

I think they can be any number < 256 but certain numbers make a lot more sense than others.

"If you have cable, open your PC's command prompt, type ipconfig, and check out your subnet mask. It's probably a /20 or /21 Class B address—yikes! You already know that translates to either 4,094 or 2,046 hosts per cable network connection. Definitely not good."
Lammle, Todd (2012-01-09). CompTIA Network+ Study Guide: Exam N10-005 (p. 502). John Wiley and Sons. Kindle Edition.
Concerning the above statement, how would you know how many hosts there are?

Is this homework? We can't do your homework for you but if you think about the length of the prefix and the length of the whole address and then what is left when you subtract one from the other, you will be well on the way.

 

[DistraughtSysop]

Subnet mask octets can only be one of the following values: 0, 128, 192, 224, 240, 248, 252, 254, 255. You'll need to understand binary in order for that to make sense - you're basically taking 8 bits and changing each bit from 0 to 1 going from left to right.

To know how many hosts are available in a subnet, you just do simple math. However, you'll really need to know how to read and make sense of a subnet mask before you can figure that out.

If you're reading the Net+ study guide, it'll explain it all. You might need through the chapter on subnetting a few times to really get it. There are loads of free online resources, too.

 

[Reckless]

Do the octets in a subnet mask have to be 255? Can it be, for example, 252? I thought they were always 255.

Your subnet mask will differ based on what Class of IP address you are using.
The subnet mask can range from 255.0.0.0 to 255.255.255.252.

"If you have cable, open your PC's command prompt, type ipconfig, and check out your subnet mask. It's probably a /20 or /21 Cass B address—yikes! You already know that translates to either 4,094 or 2,046 hosts per cable network connection. Definitely not good."

This will certainly depend on where you are and what private network you are connected to.

If you are at a university or work you will most likely be using a Class A or Class B such as 10.0.0.0 or 172.16.0.0 which YES, you can have 4094 available hosts to connect to that network.

Concerning the above statement, how would you know how many hosts there are?

There is not directly a 100% way to know how many hosts are actually connected to the network unless you setup all the computers on the network or checked the DHCP server.
You can look at the subnet mask and it will tell you the number of hosts that can connect to the network.

 

[doffins]

Sounds like I need to start all over again. ughhh!

 

[Reckless]

Subnetting is only found during the Comptia Network + or Cisco

 

[DistraughtSysop]

Sounds like I need to start all over again. ughhh!

Take your time with it. Nobody gets it right away. Are you studying for an exam?

 

[ld762]

Do the octets in a subnet mask have to be 255? Can it be, for example, 252? I thought they were always 255.

"If you have cable, open your PC's command prompt, type ipconfig, and check out your subnet mask. It's probably a /20 or /21 Class B address—yikes! You already know that translates to either 4,094 or 2,046 hosts per cable network connection. Definitely not good."
Lammle, Todd (2012-01-09). CompTIA Network+ Study Guide: Exam N10-005 (p. 502). John Wiley and Sons. Kindle Edition.
Concerning the above statement, how would you know how many hosts there are?

No, each octet in the subnet mask don't have to be 255. They can be any number between 0 to 255. But nornally you would see 0, 128, 192, 224, 240, 248, 252, 254 and 255. These are called contiguous subnet mask. All the others fall into the category of non-contiguous subnet mask which you probably won't run into.

http://www.ipinfonow.com/ipcacl.aspx has explanation about all the bits and subnet mask and how they are calculated.