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Bigun
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PostPosted: Wed Aug 21, 2013 8:06 pm    Post subject: IPV4 Class Confusion Reply with quote

So, in a perfect world (excluding the reserved addresses), the rules would be.

Code:
Class C:
First Octet between 192 and 223, CIDR notation /24

Class B:
First Octet between 128 and 191, CIDR notation /16

Class A:
First Octet between 0 and 126, CIDR notation /8


So, here's where I start to come undone. Isn't the CIDR notation subjective? For instance, what is stopping me from setting up a 192.168.0.0/16 network? Or even a 192.168.10.0/26?

Which brings me to the next question: What's the point of classes if the CIDR notation is subjective?
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szczerb
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PostPosted: Wed Aug 21, 2013 8:18 pm    Post subject: Reply with quote

AFAIR I've seen some LANs with weird masks and no DHCP. Security through obscurity, I guess.
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pjp
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PostPosted: Wed Aug 21, 2013 10:31 pm    Post subject: Re: IPV4 Class Confusion Reply with quote

Bigun wrote:
So, here's where I start to come undone. Isn't the CIDR notation subjective? For instance, what is stopping me from setting up a 192.168.0.0/16 network? Or even a 192.168.10.0/26?

Which brings me to the next question: What's the point of classes if the CIDR notation is subjective?
I'm not sure I'm understanding what you are trying to understand. /xy notation is just a different form of specifying the network.

For 192.168.0.0/16:

Netmask: 255.255.0.0
Address range: 192.168.0.0 - 192.168.255.255

For 192.168.10.0/26:

Netmask: 255.255.255.192
Address range: 192.168.10.0 - 192.168.10.63


From wikipedia:

"It appends to the address a slash character and the decimal number of leading bits of the routing prefix"

and

"Before CIDR notation, IPv4 networks were represented using dot-decimal notation for both the address and the subnet mask. Thus, 192.168.100.0/24 would be written as 192.168.100.0/255.255.255.0."
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wswartzendruber
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PostPosted: Thu Aug 22, 2013 2:39 am    Post subject: Re: IPV4 Class Confusion Reply with quote

Bigun wrote:
Isn't the CIDR notation subjective? For instance, what is stopping me from setting up a 192.168.0.0/16 network? Or even a 192.168.10.0/26?

Nothing. Go for it. You can use any subnet that lies within the private address ranges. At home, I use 172.24.0.0/24, as that lies within 172.16.0.0/12.

Bigun wrote:
Which brings me to the next question: What's the point of classes if the CIDR notation is subjective?

Classes don't serve a purpose anymore. They were eliminated to make more efficient use of the limited IPv4 address space. CIDR stands for Classless InterDomain Routing.
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Bigun
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PostPosted: Thu Aug 22, 2013 8:47 am    Post subject: Re: IPV4 Class Confusion Reply with quote

wswartzendruber wrote:
Bigun wrote:
Isn't the CIDR notation subjective? For instance, what is stopping me from setting up a 192.168.0.0/16 network? Or even a 192.168.10.0/26?

Nothing. Go for it. You can use any subnet that lies within the private address ranges. At home, I use 172.24.0.0/24, as that lies within 172.16.0.0/12.

Bigun wrote:
Which brings me to the next question: What's the point of classes if the CIDR notation is subjective?

Classes don't serve a purpose anymore. They were eliminated to make more efficient use of the limited IPv4 address space. CIDR stands for Classless InterDomain Routing.


Woah, woah, woah....... that last statement, is there an article or some kind of documentation somewhere to back that up? That would be wonderful!
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wswartzendruber
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PostPosted: Thu Aug 22, 2013 1:30 pm    Post subject: Reply with quote

http://compnetworking.about.com/od/workingwithipaddresses/a/cidr_notation.htm

EDIT: There is also no concept of a class in IPv6 networking. Have you covered anything about IPv6 yet?
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Bigun
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PostPosted: Thu Aug 22, 2013 11:43 pm    Post subject: Reply with quote

Not yet.

Now it makes sense why it was taught, but they really should have prefaced the lesson with, "Hey guys, this is the way things used to work, it's now considered legacy. But you still need to know it, so here we go".
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Bones McCracker
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PostPosted: Fri Aug 23, 2013 12:09 am    Post subject: Reply with quote

wswartzendruber wrote:
http://compnetworking.about.com/od/workingwithipaddresses/a/cidr_notation.htm

EDIT: There is also no concept of a class in IPv6 networking. Have you covered anything about IPv6 yet?

This has nothing to do with ipv6, but you want to talk about it anyway.
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wswartzendruber
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PostPosted: Fri Aug 23, 2013 1:35 am    Post subject: Reply with quote

BoneKracker wrote:
wswartzendruber wrote:
http://compnetworking.about.com/od/workingwithipaddresses/a/cidr_notation.htm

EDIT: There is also no concept of a class in IPv6 networking. Have you covered anything about IPv6 yet?

This has nothing to do with ipv6, but you want to talk about it anyway.

Well you tell me why I want to talk about it. This guy's in networking class and he's learning dinosaur shit like classful addressing when that time should be spent on IPv6 instead.
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Bones McCracker
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PostPosted: Fri Aug 23, 2013 2:56 am    Post subject: Reply with quote

wswartzendruber wrote:
BoneKracker wrote:
wswartzendruber wrote:
http://compnetworking.about.com/od/workingwithipaddresses/a/cidr_notation.htm

EDIT: There is also no concept of a class in IPv6 networking. Have you covered anything about IPv6 yet?

This has nothing to do with ipv6, but you want to talk about it anyway.

Well you tell me why I want to talk about it. This guy's in networking class and he's learning dinosaur shit like classful addressing when that time should be spent on IPv6 instead.

I once wrote a letter to my former university telling them what they should be teaching now. They never did reply. :lol:

School is about passing the tests so you can move on with your life. It's a jobs program for academics. If you actually learn anything useful in the process, consider it a bonus.
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Ahenobarbi
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PostPosted: Fri Aug 23, 2013 8:04 am    Post subject: Reply with quote

wswartzendruber wrote:
BoneKracker wrote:
wswartzendruber wrote:
http://compnetworking.about.com/od/workingwithipaddresses/a/cidr_notation.htm

EDIT: There is also no concept of a class in IPv6 networking. Have you covered anything about IPv6 yet?

This has nothing to do with ipv6, but you want to talk about it anyway.

Well you tell me why I want to talk about it. This guy's in networking class and he's learning dinosaur shit like classful addressing when that time should be spent on IPv6 instead.


Not that bad. I had a class where acknowledging existence of gigabit ethernet lost you points, answering that UDP can be used lost you points, ...

By how test looked the guy who made it didn't hear about anything what happened in computing after Windows 95 came out. I don't really know what he taught, stopped going after he spent first class talking about B.C. computing.
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Ant P.
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PostPosted: Sat Aug 24, 2013 9:58 pm    Post subject: Reply with quote

Ahenobarbi wrote:
Not that bad. I had a class where acknowledging existence of gigabit ethernet lost you points, answering that UDP can be used lost you points, ...

By how test looked the guy who made it didn't hear about anything what happened in computing after Windows 95 came out. I don't really know what he taught, stopped going after he spent first class talking about B.C. computing.

Brings back bad memories of a "computing" course I did.

They had this one multiple choice web-based exam containing questions like "which of these is a valid XML tag", which were apparently too hard for the people writing it because nearly half of them had 2 or 0 correct choices. I pointed that out, never got a reply but I did get a shitty test result along with everyone else.

There was a room full of budget-dick-waving new, overpowered machines running windows XP 64. Nothing worked on those except the crap that comes on the install CD. That was where the "web" "development" classes were held.

I'm pretty sure we were working on real, actual Windows 95 machines at one point too. Ugh.
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wswartzendruber
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PostPosted: Sun Aug 25, 2013 12:28 am    Post subject: Reply with quote

When you say Windows XP 64-bit, are you talking about the Itanium release?
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Bones McCracker
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PostPosted: Sun Aug 25, 2013 2:22 am    Post subject: Reply with quote

wswartzendruber wrote:
When you say Windows XP 64-bit, are you talking about the Itanium release?

Probably not. He's probably talking about Windows XP Professional x64.
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wswartzendruber
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PostPosted: Sun Aug 25, 2013 2:30 am    Post subject: Reply with quote

XP x64 was a damn good OS. The best thing from Microsoft I've ever used.
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Muso
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PostPosted: Sun Aug 25, 2013 2:35 am    Post subject: Reply with quote

wswartzendruber wrote:
XP x64 was a damn good OS. The best thing from Microsoft I've ever used.


Really? Better than Windows 7 64?
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wswartzendruber
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PostPosted: Sun Aug 25, 2013 2:39 am    Post subject: Reply with quote

Muso wrote:
wswartzendruber wrote:
XP x64 was a damn good OS. The best thing from Microsoft I've ever used.


Really? Better than Windows 7 64?

I think so.
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Bones McCracker
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PostPosted: Sun Aug 25, 2013 4:40 am    Post subject: Reply with quote

I don't. It sucked for lack of drivers and for shoddily-built ones.
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