Question

TCP/IP: 2 subnets, computers configured with IP of subnet 1 and SM and DG of subnet 2. Disadvantages of the configuration.

Asked by: dsterling

We have many computers on our network and 2 different subnets that we are using.

Subnet 1:
Net ID:192.168.2.0
SM: 255.255.255.128
DG:192.168.3.1

Subnet 2:
Net ID:224.168.125.0
SM:255.255.255.192
DG:225.168.125.1

The subnet masks and default gateway on some of the computers have been crossed so that some computers on the 2nd subnet have been given the subnet mask and default gateway of the first subnet., i.e. Computer 1 is configured with TCP/IP with the following: 224.168.125.25 SM:255.255.255.128, DG: 192.168.2.1, this computer is on the 2nd subnet and should have a .192 SM and use the 225.168.125.1 default gateway. The few computers we have configured this way work fine, but I'm wondering what adverse affects this may cause on our network especially with bandwidth, broadcasting, latency etc..

Im looking for a detailed understanding of why these computers need the subnet mask and default  gateway of their own subnet over the other subnet and what disadvantage it would be to have a few computers configured this way.

Server 2003 AD domain, Exchange 2003 and XP Pro environment, static IP assigned IP for all computers, servers and switches and routers.

Thank you,

This Question has been solved and asker verified All Experts Exchange premium technology solutions are available to subscription members.

Subscribe now for full access to Experts Exchange and get

Instant Access to this Solution

  • Plus...
  • 30 Day FREE access, no risk, no obligation
  • Collaborate with the world's top tech experts
  • Unlimited access to our exclusive solution database
  • Never be left without tech help again

Subscribe Now

Asked On
2009-10-31 at 13:24:10ID24861095
Topics

TCP/IP

,

Miscellaneous Networking

,

Network Routers

Participating Experts
4
Points
500
Comments
10

Trusted by hundreds of thousands everyday for fast, accurate and reliable tech support.

  • "The time we save is the biggest benefit of Experts Exchange to Warner Bros. What could take multiple guys 2 hours or more each to find is accessed in around 15 minutes on Experts Exchange." Mike Kapnisakis, Warner Bros.
  • "Our team likes having a resource that is more secure than just using Google and most experts using this service really know their stuff. It's nice to look here first versus using Google." Dayna Sellner, Lockheed Martin
  • "Anytime that I've been stumped with a problem, 9 out of 10 times Experts Exchange has either the accepted solution or an open discussion of the potential solution to the problem." Kenny Red, eBay Inc.

See what Experts Exchange can do for you.

Got a question?

We've got the answer.

Experts Exchange has been collecting answers to technology questions since 1996…3 million and counting! If you have a question, chances are we already have your answer.

Screenshot of Experts Exchange Knowledgebase

Need individual assistance?

Our experts are ready to help.

If you can't find the exact answer you're looking for, ask our exclusive community of 50,000 experts. You’ll get a personalized answer from a trusted professional.

Screenshot of Experts Exchange Knowledgebase

Want to learn from the best?

Read articles from industry experts.

Thousands of free tech tips, tricks, how-to’s and tutorials are available in our peer reviewed articles section. See for yourself how smart our experts are, no login required.

Screenshot of an Article

Working on a long term project?

Store your work and research.

Save solutions to your questions, answers you’ve discovered through searching plus helpful articles in your personal knowledgebase for easy future access.

Screenshot of Experts Exchange Knowledgebase

Access the answers to your technology questions today.

Subscribe Now

30-day free trial. Register in 60 seconds.

What Makes Experts Exchange Unique?

Members of the expert community talk about why the experience at Experts Exchange is different than what you will find anywhere else.

Trusted by the world's most respected brands.

image of each brand's logo

Faithfully serving IT professionals since 1996.

Experts Exchange Logo

Try it out and discover for yourself.

Subscribe Now

30-day free trial. Register in 60 seconds.

Related Solutions

  1. SMS
    Where can I get (free) development resource for SMS or SMS with image ? Andrew
  2. route to different DG
    I have a test network using 192.168.255.0/24 Default GW: 192.168.255.251 I want to setup a clients server using 192.168.1.0/24 DG: 192.168.1.251 The clients machine will work fine on its own network. Is their a way that I can set it up on my test network and temporaraly fo...
  3. SMS ...
    How to send SMS from the Web ?

Free Tech Articles

  1. WARNING: 5 Reasons why you should NEVER fix a computer for free.
    It is in our nature to love the puzzle. We are obsessed. The lot of us. We love puzzles. We love the challenge. We thrive on finding the answer. We hate disarray. It bothers us deep in our soul. W...
  2. SCCM OSD Basic troubleshooting
    SCCM 2007 OSD is a fantastic way to deploy operating systems, however, like most things SCCM issues can sometimes be difficult to resolve due to the sheer volume of logs to sift through and the dispe...
  3. Migrate Small Business Server 2003 to Exchange 2010 and Windows 2008 R2
    This guide is intended to provide step by step instructions on how to migrate from Small Business Server 2003 to Windows 2008 R2 with Exchange 2010. For this migration to work you will need the fo...
  4. Create a Win7 Gadget
    This article shows you how to create a simple "Gadget" -- a sort of mini-application supported by Windows 7 and Vista. Gadgets can be dropped anywhere on the desktop to provide instant information, ...
  5. Outlook continually prompting for username and password
    There have been a lot of questions recently regarding Outlook prompting for a username and password whilst using Exchange 2007. There are a few reasons why this would happen and I will try to cover t...
  6. Backup Exchange 2010 Information Store using Windows Backup
    There seems to be quite a lot of confusion around the ability to backup Exchange 2010 using the built in Windows Backup feature. This stems from the omission of this feature prior to Exchange 2007 s...

Cloud Class Webinars

  1. Avoiding Bugs in Microsoft Access
    Alison Balter takes and in-depth look at avoiding bugs in Access. In this webinar you will learn about using the immediate window to debug your applications, invoking the debugger, using breakpoints to troubleshoot, stepping through code, setting the next statement to execute, ...
  2. Top 10 Best New Features in Visio 2010
    Scott Helmers gives live demonstrations of the top 10 new features in Visio 2010. This webinar will teach you how to create compelling diagrams by adding shapes to the page with a single click, linking the shapes in a diagram to data in Excel (or SQL Server, or SharePoint), ...
  3. IT Consultant Business Secrets Revealed
    Michael Munger, Experts Exchange tech pro and IT consultant, pulls back the curtain on his very successful businesses and answers question on every IT consultant and business owner should know about. He shares secrets on what he did to solve the 5 most common problems in IT, ...
  4. Disaster Recovery and Business Continuity
    Quest CTO, Mike Billon, gives an overview of the steps involved in building a dunamic disaster recovery plan. Through case studies and an examination of software/hardware tooles for monitoring and testing, you'll gain a better understandin of where you are, where you want ...
  5. Organize Your Visio Diagrams with Containers and Lists
    Scott Helmers uses cross functional flowcharts, wireframe diagrams, data graphic legends and seating charts to teach you: how to ustilize all three new structured diagram components in Visio 2010, the best practices for organizeing shapes in previous version of Visio, how to organize ...
  6. How to Us Objects, Properties, Events and Methods in Microsoft Access
    Alison Dalter gives an in-depbth look at objects, properties, events and methods in Microsoft Access. In this webinar you will learn about using the object browser, referring to objects, working with properties and methods, working with object variables, understanding the ...

Join the Community

Give a Little. Get a Lot.

Join the community of experts here and help other tech pros by answering question in your area of expertise. You can earn FREE access to all Experts Exchange's premium features and resources.

Join the Community

Answers

 

by: MikeHolcombPosted on 2009-10-31 at 13:32:12ID: 25711430

It looks like someone got a little over zealous with your subnetting.  While technically these subnet masks could work, they do make troubleshooting network connectivity much more complicated - as you're experiencing.  I would strongly suggest re-addressing the network to conform with the standard subnet masks defined for internal networks according to RFC 1918 (http://en.wikipedia.org/wiki/Private_network).

I would simplify Subnet 1 and use 192.168.1.0 with a standard subnet mask of 255.255.255.0 which allows for 254 hosts on that one subnet.  You could use 192.168.1.1 as your default gateway.

Considering Subnet 2 is not even using a private IP address, I would change it completely to another subnet such as 192.168.2.0 with a subnet mask of 255.255.255.0.

I come across a lot of customers with "strange"  subnet mask address schemes and in the end, they are very happy when they invest the time to re-addressing their systems.

Hope this helps...

Mike

 

by: e_vanheelPosted on 2009-10-31 at 13:44:36ID: 25711465

The Default gateway MUST be on the same subnet as the host.

The computer only knows how to talk to "local" computers.  The purpose of the default gateway is a local computer that knows how to get to other networks.

The local computer compares the address for a packet and determines if it is local - if it is it sends directly to the at host, if it is not local it checks it's routing table if nothing is found it forwards that packet to the default gateway

hope that helps!

 

by: SulimanwPosted on 2009-10-31 at 15:29:48ID: 25711851


computer1:
ip:  224.168.125.25
SM:255.255.255.128
DG: 192.168.2.1

that means: computer1 can communicate only with all computers has ip addresses rang (224.168.125.1 to  224.168.125.1.127) which is in the same subnet, so computer1 will never communicate with default gateway you assigned to it because 192.168.2.1 is out of rang.

you can easily add additional ip address in computer1 from the first subnet ( 192.168.2.0/25), then all this will go fine .

 

by: dsterlingPosted on 2009-11-01 at 01:59:46ID: 25713066

These IP subnets have been assigned to our network and are part of a much larger network, I can't change the subnets, also they are not the actual subnets in the example I gave for security reasons, sorry, I should of explained that.

What happens with data when a computer on the incorrect subnet and default gateway send to a local computer outside of the correct subnet, but inside the incorrect subnet? i.e. computer 224.168.125.25 (with its incorrect .128 subnet and incorrect dg 192.168.2.1 send a message to computer with correct TCP/IP config with IP 224.168.125.115? Since the correct subnet allows for host 224.168.125.1 - 224.168.125.62, the computer receiving the message is outside of the correct subnet, but inside the incorrect subnet (.128 (224.168.125.1 - 224.168.125.126)) Hope this is a better explanation of what I'm getting at.

Thank you,

 

by: Rick_O_ShayPosted on 2009-11-01 at 04:46:24ID: 25713535

If just the mask is wrong then the PC thinks the device is local due to the wider range allowed by its incorrect mask and it will not send the packet to the default gateway. It will just arp for the address that is really off the local subnet and get no reply.

 

by: dsterlingPosted on 2009-11-01 at 05:32:36ID: 25713651

Rick O Shay:
If that is the case, then why do the computers with the incorrect mask and dg work on the network and are able to send local email to other computers and connect to local network shares?

 

by: e_vanheelPosted on 2009-11-01 at 05:42:52ID: 25713672

They can't via TCP/IP.  

Can you post the results from a ping from a computer that has the wrong DG set to a computer on the other subnet?

There are other options that might make this work.
Any chance you have other protocals installed - IPX/SPX, etc?
Do the servers have more than one IP address - another address that is "local" to the second subnet?
a router the forwards all traffic to this network.

 

by: dsterlingPosted on 2009-11-01 at 06:06:48ID: 25713717

Please don't accuse me of lying, it does work! I''ve changed the settings, but i'm wondering why it work with the incorrect setting, I will give points soon.

Thank you everyone for all the comments, I think I have a idea why it works and I believe it's causing more network traffic because of the incorrect settings, the incorrect settings work because both default gateways are on the same router that both sub-nets use, in fact they are on the same interface, with sub interface settings for the second subnet. The incorrect sm causing the computer to look for the local computer and when it can't find it on the local subnet it directs traffic to the default gateway whicn in turn directs it to the computer, so the extra traffic is created, because the incorrect settings don't allow for a direct path to the other computer it trying to send data too. I think this may be more of a Cisco Switch and Router issue when trying to understand what is going on. Any comments are still appreciated, agree or diagree?  

 

by: e_vanheelPosted on 2009-11-01 at 06:14:58ID: 25713736

Please don't take what I said as accusing you of lying.  It obviously works - just not like it should.

What I said (or meant to) was via tcp/ip the configuration will not work if:

1 - The computers are on a different subnets
2 - The default gateway is on a different subnet than the computer

I think you are on to something with your router - like I asked above - it appears that you might have 2 addresses on your router (server).  

You are correct that it is not idea from a data perspective because your switch or router is involved when it does not need to be.

I would recommend cleaning up the IP addresses and simplifying it if you can.

 

by: dsterlingPosted on 2009-11-01 at 06:40:04ID: 31648438

Thanks for all the comments, appreciate all the effort to come to a understanding of this, I do think that I have a satisfactory understanding of this now and all the comments were very helpful.

20120131-EE-VQP-002

3 Ways to Join

30-Day Free Trial

The Experts

98% positive feedback on 31,087 answers since March 2000. angeliii is a Microsoft Most Valuable Professional for his work with MS SQL Server & Develoment.

He has also proven his knowledge of Visual Basic Programming, PHP Scripting and Oracle Databases.

The Experts

97% positive feedback on 10,752 answers since July 2000. lrmoore has more than 18 years experience in the networking industry.

The six-time Mircosoft MVPs specialties include firewalls, virtual private networking, and network management.

Testimonials

"...and excellent source for support... Kind of like having your very own IT dept." Electriciansnet

Testimonials

"I was apprehensive at signing up at first. However... it has already made my life as an IT administrator much easier." JaCrews

Testimonials

"WOW! You guys have great, active, and knowledgeable people on here." moore50

Business Clients

Business Clients

In the Press

"If you’ve got a question... Experts Exchange can supply an answer.”

In the Press

"...an invaluable aid for both IT professionals and those who require tech support."

In the Press

"where IT professionals provide quick answers on just about any topic"

Business Account Plans

Loading Advertisement...