what is the meaning of host portion?

Reoroman - Being a cisco engineer and fan for many years, I always find ciscos explanation of subnetting to be fairly straight forward.  Take a look at this link and see if it makes a bit more sense:  

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f33.shtml

I will follow your question and try to add more clarity as you need.

Best regards,
Brian

I think you understand this part: (from the wiki)

 "IP address is logically divided into two fields, a network field and the host field. All hosts on a subnetwork have the same network prefix."

For details, check:  http://en.wikipedia.org/wiki/Subnetwork#IPv6_subnetting

Let us know if you need more.

thank you i will check the link... many thanks for quick reply

I cannot understand it ?? what is it refer to ????... i know how to find subnets and hosts per subnet, find valid subnets, broadcast address for each subnet, valid hosts.
I know exactly what is the purpose of every one. but I do now know the purpose of host portion, its easy to memories it and calculate it, but if someone asks me what is it for ???? what should i answer??

respect

sorry i mean i do not know the purpose of host portion, its easy to memories it and calculate it, but if someone asks me what is it for ???? what should i answer??

The host portion is the portion of ip address that is assigned to the individual device.  For example, if my computer has the ip address of 192.168.1.150 with a subnet mask of 255.255.255.0, the host portion is .150 - it is the portion that determines the unique device.  The rest of the address is the network portion used by routers to route (direct) packets to that network then the host portion identifies the final destination - or device - the packets are destined for.  I hope this makes sense :-)

Best regards,
Brian

That is good Brian.  I'll add that the host portion is a range of numbers and it determines how many hosts can be on that network. (network portion)  So the big companies (ie. networks with tons of hosts) will need to have a larger host range. (ie. smaller network mask: 255.255.128.0) vs a small network that only needs a few IP addresses and can have a smaller host range (ie. larger mask 255.255.255..64).  

Oh, and one more thing.   A company will basically pay more for the IP address if it can have more hosts on it.  (ie the network portion is smaller and the host portion is bigger).  The old way is to use classes (A,B,C) as is shown on the wiki.  

Does that make it any better?

Yesterday I wanted to reply but experts-exchange website was offline for technical updates on the website.
Dears milehijones, you said The host portion is the portion of IP address that is assigned to the individual device. For example, if my computer has the IP address of 192.168.1.150 with a subnet mask of 255.255.255.0, the host portion is .150   OKAY! So why then I have to do the math to find host portion why do I have to bother my self-calculating host portion as it’s mentioned in the website: http://www.subnetmask.info 
Let me check with you two examples:
First example:   192.168.1.150 255.255.255.0
To get the host portion, invert the subnet mask and again perform a binary AND with the ip address:             IP address:                 11000000.10101000.00000001.10010110
Inverted subnet mask: 00000000.00000000.00000000.11111111
                  -----------------------------------AND
        Host portion:        00000000.00000000.00000000.10010110
Which translated back to dotted decimal notation is 0.0.0.150  

Second example: 192.168.1.150 255.255.255.224
To get the host portion, invert the subnet mask and again perform a binary AND with the ip address:
          IP address: 11000000.10101000.00000001.10010110
Inverted subnet mask: 00000000.00000000.00000000.00011111
                  -----------------------------------AND
        Host portion: 00000000.00000000.00000000.00010110
Which translated back to dotted decimal notation is 0.0.0.22

So why host portion here is 0.0.0.22 while in the first example 0.0.0.150???????
If this host portion should be done as you mentioned so in the second example host portion should be 0.0.0.150 not 0.0.0.22!!!!
Can you explain that?
Thanks

Brilliant … you explain it like no one can do. :-)

                   Many thanks.

You welcome.  Glad we got it.  Thanks for the points.  I'm now only 3600 pts from a sage!