?
Solved

simple subnetting question

Posted on 2003-12-04
5
Medium Priority
?
325 Views
Last Modified: 2010-03-19
In the following site http://www.learntosubnet.com/Subnetting_Step2.htm

# Of Hosts per SN-ID

128-2 = 126 (Invalid)
64–2 = 62
32–2 = 30
16-2 = 14
8–2 = 6
4-2 = 2
2–2 = 0 (Invalid)
0 (Invalid)

I have no idea why 126, 0 are invalide number of hosts. I appreciate any help.

Thanks
0
Comment
Question by:aja101498
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
5 Comments
 

Expert Comment

by:cf_root
ID: 9879070
I am not sure why they are listing 126 as invalid. Because technically with that subnet mask you have 126 available address. The 2 unusable addresses are for your broadcast and network. That is why the "2-2" is not valid. One is the network the other is the broadcast address therefore no hosts can reside on this mask. Please let me know if you have questions.
0
 
LVL 18

Expert Comment

by:chicagoan
ID: 9879301
/25 is a valid mask
0
 
LVL 7

Expert Comment

by:MaB
ID: 9880830
They are probably listing 126 as invalid because with a class C net subnetted into two 128 subnets with 126 possible hosts in each subnet that would mean that the first subnets network adress would be X.X.X.0 which is the same as the class C nets network address which is "no good".
Similar reason with the second subnet which will have X.X.X.128 as network adress which is "legal" but X.X.X.255 as broadcast adress which is the class C nets broadcast address thus also "no good".

You will always lose the first and last subnet as "no good" when subnetting.

See more extensive description in http://www.experts-exchange.com/Networking/Q_20816228.html#9874506
0
 
LVL 7

Expert Comment

by:MaB
ID: 9880834
0 is invalid because you wont have need for a subnet that can't have ane hostes attached.
0
 
LVL 18

Accepted Solution

by:
chicagoan earned 200 total points
ID: 9881954
This is a limitation of the windoze ip implementation, not because some other subnet class uses them as a network address or broadcast address. Using that logic a .252 mask would invalidate 124 addresses in a .255 network.
Supernetting always yields 0 and 255 host addresses, and these should be reserved in your allocation table for that reason.
0

Featured Post

Connect further...control easier

With the ATEN CE624, you can now enjoy a high-quality visual experience powered by HDBaseT technology and the convenience of a single Cat6 cable to transmit uncompressed video with zero latency and multi-streaming for dual-view applications where remote access is required.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This article will inform Clients about common and important expectations from the freelancers (Experts) who are looking at your Gig.
This article is in regards to the Cisco QSFP-4SFP10G-CU1M cables, which are designed to uplink/downlink 40GB ports to 10GB SFP ports. I recently experienced this and found very little configuration documentation on how these are supposed to be confi…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
Suggested Courses

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question