TCP/IP and Subnetting

[Tarrant64]

I'm trying to understand a couple things about subnetting at the moment. I'm taking a network comm. class and we have 1 week dedicated to TCP/IP. It's crucial I get most(if not all) understanding of it, as once I'm done with this class I have one whole class dedicated to TCP/IP. Anyways, to the problem.

I've been given an IP address, 202.16.105.27 with a subnet mask of 255.255.255.248. I'm asked questions as to what I know about the class, default subnet, etc. about it.

This is what I have so far. Class C, default subnet of 255.255.255.0(for class C).
Now, what has thrown me off is 202.16.105.27 /29.

I ran across it in my reading but only for a paragraph or so. I wanted to say that it supports 30 sub networks, and supports 2,046 hosts.

I was thinking the network address and broadcast address would be easy too, just 202.16.105.0 and the broadcast address is 202.16.105.255

Can someone help me out?

 

[spyordie007]

The /29 is shorthand for 255.255.255.248 (29 consecutive bits flipped on)

The network is 202.16.105.24, broadcast is 202.16.105.31 and there are only 6 addresses for hosts.

Sounds like you need to learn more about subnetting in binary before you move forward, if you do this will make a lot more sense.

Erik

 

[spyordie007]

A quick Google search got me this, has some good info on binary math and subnetting:
http://www.learntosubnet.com/

 

[Tarrant64]

Thanks a lot for the link. When I did go back through and concentrated on the binary aspect of subnetting it made more sense. "/29" wasn't covered in the reading, but it was online in a few places but it was never really explained to be 'shorthand'. After going through the binary, it was a "duh" moment.

11111111 11111111 11111111 11111000 - >29 bits, or 255.255.255.248, right?

The subnet is 3 bits long, so 2^N gives me 8. Subtract 2 and we get 6, the number of hosts.

Using AND I got 24, which is as you say the network ID, and 31 is as you say the broadcast address. Makes a lot more sense now. The website linked had a few practice examples which helps too. It was mainly the AND that wasn't covered in my book and a couple of websites didn't have it either, but that one did the trick!

Thanks.

 

[jlazzaro]

yup...and instead of using powers, just subtract the last subnet octet from 256 to get the total number of hosts.

256 - 252 = 4
256 - 248 = 8
256 - 240 - 16
256 - 224 = 32
256 - 192 = 64
256 - 128 = 128

 

[compman25]

Originally posted by: jlazzaro
yup...and instead of using powers, just subtract the last subnet octet from 256 to get the total number of hosts.

256 - 252 = 3
256 - 248 = 8
256 - 240 - 16
256 - 224 = 32
256 - 192 = 64
256 - 128 = 128

😕

 

[jlazzaro]

lol typo, leave it alone ;x

 

[Ninjazx]

Originally posted by: jlazzaro

256 - 252 = 3

must be that 'new math' i'm having a hard time with. 😉