Ip address/subnet

mister_417

I start learining ccent i have problem with topic ip/subnet can you help me?
[FONT=&quot]Which subnet does host 172.45.188.29 255.255.255.0 belong to? First i write number with binary and second step problem[/FONT]
[FONT=&quot]What is the last valid host on the subnetwork 172.40.36.0 255.255.254.0?[/FONT]

rob42

You need to get your head around what the 'mask' means.

With your first example, 255.255.255.0 means that the first three octets [255.255.255] identify the Network, while the last octet [0] identifies the Nodes. So, with your IP Address, 172.45.188. is the Network ID and .29 is the Host ID.

With that Network, the IP Address range is 172.45.188.0 to 172.45.188.255

The first address is always the Network Address and the last address is always the Broadcast Address, leaving 172.45.188.1 to 172.45.188.254 for Host IP Addresses.

Looking at the mask, 24 bits have been assigned to the Network (that is 3 Octets, 8 bits per Octet: 8*3 = 24), leaving 8 bits for the Nodes.

The mask binary will look like this 11111111|11111111|11111111|00000000

2^8 = 256. 256-2 = 254 Hosts; remember, we need '0' for the Network ID and '255' for the Broadcast Address.

The math is relative in order to understand your second example...

With your second example, the mask is 255.255.254.0. This increases the number of hosts, while at the same time decreasing the number of Subnets (Network IDs), because we now have an extra 'bit' from the 3rd Octet.

The mask binary will now look like this 11111111|11111111|11111110|00000000

Notice, 9 zeros, not 8.

2^9 = 512. 512-2 (just as before) = 510 Hosts.

So, Network 172.40.36.0 can have up to 510 Hosts, but we can't have an IP of 172.40.36.510, so when we get to 172.40.36.255, we have to carry over to the next significant Octet (the one to the left) resulting in 172.40.37.0

We can do this all the way up to 172.40.37.255; the Broadcast Address, the last valid Host being one less than the Broadcast: 172.40.37.254.

Try searching this forum for this type of question. You'll find it's quite a common question and has been explained umpteen times, in many different ways.

mister_417

Thank you!

rob42

You are very welcome.

I've just seen your next post URL]http://www.techexams.net/forums/ccna-ccent/123259-vlsm-summariration.html#post1058627[/URL. That's a BIG LEAP!!, from not understanding basic Subnetting to VLSM. Wow!!!

mister_417

I understading ip address/subnet because i have one problem when i write to binary second step will problem.I read your answer and problem will compled.