Subnet mask questions

[pollardhimself]

Some one gave me this address 10.137.254.10 and said it was a class C when I ask for the subnet mask. Isn't that a class A Address? I am weak on sub netting. Is that even enough to figure out the mask don't I need to know the amount of subnets to even get the mask.

😵 I need to take a networking class!

 

[Fallen Kell]

Class C typically means "Class C is defined with the 3 high-order bits set to 1, 1, and 0, and designating the next 21 bits to number the networks, leaving each network with 256 local addresses.", which typically means a netmask of "255.255.255.0" since you are only addressing 256 local addresses.

 

[ViviTheMage]

I would ask for the subnet mask, not what class it is. Class C could be anything... 255.255.255.0, or 255.255.255.128, etc

 

[drebo]

Class C typically means "Class C is defined with the 3 high-order bits set to 1, 1, and 0, and designating the next 21 bits to number the networks, leaving each network with 256 local addresses.", which typically means a netmask of "255.255.255.0" since you are only addressing 256 local addresses.

That's the canonical definition of "class c" which has never actually been used on the Internet.

Unseasoned, naive, or stupid network techs typically (incorrectly) use "Class C" to describe a /24 network (a network with a mask where the first 24 bits are 1, e.g. a mask of 255.255.255.0).

It is, however, neither a Class A nor a Class C address or network. It is, simply, a /24 network.

Pro tip: Classful networking has never been used and should not be referred to in any way. Use CIDR notation to describe networks, because it's the most precise way. It should have been specified as 10.137.254.10/24.

Ignore the fact that there ever was a time before VLSM and CIDR and ignore the fact that IP addresses were ever divided into "classes".

 

[pollardhimself]

That's the canonical definition of "class c" which has never actually been used on the Internet.

Unseasoned, naive, or stupid network techs typically (incorrectly) use "Class C" to describe a /24 network (a network with a mask where the first 24 bits are 1, e.g. a mask of 255.255.255.0).

It is, however, neither a Class A nor a Class C address or network. It is, simply, a /24 network.

Pro tip: Classful networking has never been used and should not be referred to in any way. Use CIDR notation to describe networks, because it's the most precise way. It should have been specified as 10.137.254.10/24.

Ignore the fact that there ever was a time before VLSM and CIDR and ignore the fact that IP addresses were ever divided into "classes".

My sub netting is sub par, but I thought him telling me was class c was stupid when I asked for the subnet mask. "He was being kind of a !@#$" I replied back to him and said, " is 255.255.255.0 correct class c isnt enough to go on I need to know the amount of subnets you have". He eventually called me back and said yes if it wasnt that it wouldnt be class c which didnt sound right to me either but this guy works for northrop grumman IT department so I didn't question him anymore since I wasn't positive I was right.

 

[alkemyst]

Classful networking was indeed used long ago.

However, when one refers to a 'Class C' today it's almost always referring to a /24. 255.255.255.0 subnet mask.

It's the whole magazine vs clip debate, you can be a dick and argue about it; but the fact is these terms are embedded in many professionals vocabularies.

 

[imagoon]

Even the seasoned guys will use "class A / B / C" for /8 /16 and /24 respectively. Anything else we say "slash 'insert bit count here'" here.

We all know that it doesn't mean anything with CIDR [anymore]. Heck if it did what about Class D and E?

 

[ViviTheMage]

Even the seasoned guys will use "class A / B / C" for /8 /16 and /24 respectively. Anything else we say "slash 'insert bit count here'" here.

We all know that it doesn't mean anything with CIDR [anymore]. Heck if it did what about Class D and E?

That is the proper way, IMO.

 

[imagoon]

That is the proper way, IMO.

I think the main issue is they still teach CIDR in school. Old habits die hard. I had an 19 year old cousin talking about it from class. You won't see the nomenclature dropped until the professors that lived through arpanet retire. One of the reasons I picked it up is because "class C" seems to mean more to most people than "slash 24" where I get blank looks. Obviously Pros don't this issue but a lot of the younger people I have worked with understand it still.

 

[MtnMan]

😵 I need to take a networking class!

uuuuuh yep, and it's pretty much all CIDR now.

 

[Railgun]

One of the reasons I picked it up is because "class C" seems to mean more to most people than "slash 24" where I get blank looks. Obviously Pros don't this issue but a lot of the younger people I have worked with understand it still.

Even then, more often than not I need to spell it out for some that aren't on the network side of IT. Especially if anything smaller than a /24.