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Can 10.50.0.0/16 ping 10.0.0.0/8 each other?

Posted on 2002-03-12
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Last Modified: 2009-12-16

I have two PCs, A and B on a hub.
A is 10.50.x.x and a netmask of 255.255.0.0 while B is 10.x.x.x with a super netmask of 255.0.0.0

Can A ping B and vice-versa without a router?
Please explain in detail.

Thanks!

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Question by:thiamwah
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11 Comments
 

Expert Comment

by:mbroaders
ID: 6856905
I wouldnt think so. The two PCs specified are configured to be on on seperate subnets which will not allow them to ping each other.

By giving A a "class B" subnet mask you have said that it is in network 10.50.x.x where 10.50 is the network and x.x is the host.
By giving B a "class A" subnet mask you have said that it is in network 10.x.x.x where 10 is the network and x.x.x is the host.

For two PCs to communicate without the use of a router they will need to be on the same subnet.

If you wish to enable the two pcs to communicate with each other i would suggest changing B to have an IP address of 10.50.x.x with a subnet of 255.255.0.0

Hope that helps

MB
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Expert Comment

by:ahoffmann
ID: 6857198
depends on the OS. M$ definitely cannot not. Most UNIX can, while Linux is somwhere inbetween, unfortunately.
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Accepted Solution

by:
helmet_js earned 30 total points
ID: 6863465
A given host on a network uses the combination of its own IP address and its netmask to determine if an address is on the same network as itself.  If it is, the device will send out an ARP request which is an ethernet (layer 2) broadcast (FF-FF-FF-FF-FF-FF) to find the hardware address of the other host.  All NIC cards listen for this MAC by default.  The other host will respond directly to the device making the ARP request with its hardware address.  Now, how does this apply to your question?  If host A tries to talk to host B and the address of host B is not between 10.50.0.0 and 10.50.255.255 the device will not ARP for host B but will instead look at its routing table to determine how to get to that destination.  If by chance the address of host B IS in the range 10.50.0.0 to 10.50.255.255 host A WILL arp for host B and host B will respond thus allowing them to communicate.  Of course host B will arp for anything between 10.0.0.0 and 10.255.255.255 but two way communication can only be established if B's address were to be within the 10.50 range.  As a side note, it is best to match all hosts on a network with the same netmask.  Especially if you care about accessing resources outside your local network.
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Expert Comment

by:stevenlewis
ID: 6866792
You should really read your book, and study. We should not do your homework for you
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Author Comment

by:thiamwah
ID: 6879920
ok, let us assume that B is indeed 10.50.x.x with a (super) netmask of 255.0.0.0 while A is 10.50.x.x with a netmask of 255.255.0.0

helmet,
from ur explanation it would seem that it would be able to ping each other... since B is within the 10.50 range..
Please confirm.

BTW, this is not homework!! Just some (weird?) questions I try to understand from time to time... :)
 
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Expert Comment

by:helmet_js
ID: 6880233
Just so you know, 255.0.0.0 is NOT a "super" netmask for a class A address.  If you are talking classful addressing the "native" mask for a class A address is 255.0.0.0 (/8), a class B address is 255.255.0.0 (/16), and a class C is 255.255.255.0 (/24).

And yes, they would be able to ping each other.  The only 2 addresses in 10.50 that would not work on network B are 10.50.0.0 (because it is the subnetwork address for network A (but is a valid host address on network B)) and  10.50.255.255 (which is the subnetwork broadcast address for network A (but is also a valid host address on network B)).  All other addresses, which are all of the valid host addresses on network A, 10.50.0.1 through 10.50.255.254 will work.
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Expert Comment

by:ahoffmann
ID: 6880299
> All other addresses, .. on network A, 10.50.0.1 through 10.50.255.254 will work.

No, not for M$ hosts (not shure about w2k), except someone exchanged the TCP/IP stack there.

In theory, theory and praxis are identical. In praxis they are not :-|
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Expert Comment

by:helmet_js
ID: 6880370
I know you are mistaken.

In regards to this, there is NOTHING special with Microsoft.

Thank you, please drive thru.
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Expert Comment

by:helmet_js
ID: 6880371
I know you are mistaken.

In regards to this, there is NOTHING special with Microsoft.

Thank you, please drive thru.
0
 
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Expert Comment

by:stevenlewis
ID: 6881320
helmet_js  ! Welcome to E-E! Its common courtesy to provide comments unless you know your answer is the only answer and is 300% correct and is what the questioner is looking for and will fix their problem. Please don’t take this personally, (others could let you know before I and not so diplomatically) I made the same mistake when I first arrived and someone was nice enough to point it out to me (It hurt my feelings, but I soon realized its teamwork that’s used here). This accomplishes a couple of things: First: it doesn't lock the question allowing more exposure to other experts allowing a faster fix (many problems require an interactive dialogue to troubleshoot them properly), Secondly: it gives the questioner the option to make an award based on the best comment that helped the most in fixing their problem and it is also is common courtesy to other experts.  Again welcome and look forward to working with you in the future, a lot of teamwork is used at this forum, as you will see! :>)  Quote shamelessly stolen from Dave, Thanks again Dave

Your answer may be correct, and I hope it is, after all the main goal here is to help the questioner, but when you propose an answer it removes the "accept comment as answer" button thereby robbing the questioner of the choice to choose which expert helped the most. If your comment is chosen by the questioner, you will be awarded the points.
Thank you  
Steve  





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Author Comment

by:thiamwah
ID: 6882291
thxs helmet for ur good answer.
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