Newb question. What does the /24 specify?

[Haleon]

In this example:

192.168.1.1/24

Is that the subnet or something? What's it called?

 

[jimbopalmer]

/24 indicates the subnet mask is 255.255.255.0

in binary, it has 24 1s and 8 0s

11111111111111111111111100000000

so a /16 would be 255.255.0.0


11111111111111110000000000000000

I tried to remain child-like, all I acheived was childish.

 

[KiscoKid]

a.b.c.d/24 is called CIDR notation. It's Google-able.

 

[cyberspace]

Also, FYI:

/24 - Default Class C subnet mask (255.255.255.0)
/16 - Default Class B subnet mask (255.255.0.0)
/8 - Default Class A subnet mask (255.0.0.0)

'When all else fails.......read the manual'

 

[wasisnt]

Its just a shortcut way to tell you what the subnet mask is.

Free Computer Help and Tips:

http://www.onlinecomputertips.com/

 

[chieftan]

CIDR = Classless Inter Domain Routing

Or you could call it VLSM

Variable length Subnet Masks

Either way, it means you can subnet your network more effectively.

 

[Haleon]

Thanks for all the replies, guys!

I spent a couple of hours going over subnetting in detail, so I feel comfortable with the general premise of creating custom subnet masks and then referring to the subnets by their subnet IDs, but I still am confused about a couple of things.

Is it possible to take a class C address and apply a subnet mask that is less than 24 bits to it? Or can you only ADD bits to a subnet mask?

Also, I've seen a network with a private class A address (10.0.0.0) subnetted with a class C default subnet mask. I was under the impression that you could only customize the subnet mask to the next octet in the mask. Can you go even further than that?

I appreciate the help guys!

 

[leedsit]

Hi, yup, you could take a Class C address and reduce the mask if you wish, known as Supernetting. and also you can summarize ( CIDR ) address ranges on routers to cover routes for ranges of Class C.

I.E

192.168.0.0 /24 ( Class C ) = around 254 nodes
192.168.1.0 /24 ( Class C ) = around 254 nodes

Supernet to
192.168.0.0 /23 = around 512 nodes
Range
192.168.0.0 to
192.168.1.254

OR

192.168.0.0 /22 = around 1024 nodes
Range
192.168.0.0 to
192.168.3.254

On a router, If you have 4 class C address routes

192.168.0.0 /24
192.168.1.0 /24
192.168.2.0 /24
192.168.3.0 /24

Instead of having 4 separate routes in the routing table you could use CIDR and have one entry representing the whole range

192.168.0.0 /22

Of couse the same applies with class B`s, A`s etc...





LEEroy
MCNE6,CCNA2,CWNA, Project+

 

[jimbopalmer]

1) Yes, I have seen clients who, when they ran out of 192.168.1.x addreses, just widened their mask to allow 192.168.0.x to 192.168.7.x addresses

2) Yes, a great many 'large' organizations are 10.x.x.x worldwide, although each remote site may use a 255.255.255.0 mask. The local router can send all other 10.x.x.x addresses to Corporate Headquarters and all other addresses to the Internet.

So a real estate agenty may be 10.199.237.x and all local devices are in the subnet, but an address like 10.0.100.50 may be a mail server at the world headquarters. By using a 255.255.255.0 mask it knows that the mail server is not local. The local router can have a default route of the internet and a 10.0.0.0/8 route to the main router at corporate.

In this scenario, one usually has a VPN back to Corporate (and a firewall to the internet)


I tried to remain child-like, all I acheived was childish.