IP subnetting exceptions

Hi all

if u know some thing about ip subnetting u must be aware of the fact that if we devide a perticular network address into subnet and assign two ipaddresses from diffrent subnets ,then those two host must not be able to communicate
for example

take a n/w address 192.168.10.0
subnet mask 255.255.255.0


lets devide this in to subnets ,each with block of 32 ddresses ,thus we get the following

255.255.224.0----subnetted subnet mask

192.168.10.0 first network

192.168.10.32 second network

192.168.10.64 third network
.
.
.
.
.
and so on .....
all those with subnet mask 255.255.255.224

ilets take two pcs and assign them following address

pc1--
ip -> 192.168.10.1
subnet mask 255.255.255.224


pc2
ip -> 192.168.10.33
subnetmask 255.255.255.224



NOW....
if we try to make communucation between these two .....what will happen?
obviously both will not going to communicate

b coz network address are different for both the pcs.
and as they on diffrent network they cant communicate


BBBBUUUTTTT

there are some exceptions

take an n/w addres 191.168.10.0/29


and perform subnetting
we can communicate between two pcs inspite of assigning ip addresses from two different network .


i cant understand why in some examples it is violating the concept.



can any one help me?????

 

im not really sure if this is what youre asking, but you need a router to communicate between subnets.

and something i learned about in my routing/switching class is that when youre subnetting youre not supposed to use the first and last subnetted ip ranges because it will have some kind of effect on how the computer sees that its subnetted. like the network address of 192.168.1.0. the .0 is the network address whether its useing the default 255.255.255.0 mask or your subnetted 255.255.255.224 mask. so i think it wont even see that its subnetted and wont be able to communicate between the subnets.
i was told to drop the first and last ranges for that reason. so with the mask of .224 youd want to start with .32 as the first network address, .33 as the first host address in that subnet and so on.

 

Steve King is correct,
EXCEPT
When using Cisco Routers. Cisco allows you to use IP SUBNET ZERO. Which means that you gain both the first and last network.
Yeah for Cisco!

 

well heres an edit to my last post. what would happen if you used the first and last ip ranges is that when you had for example a mask of 255.255.255.192 and you used 192.168.1.255 for the broadcast of your last subnet, the computer wouldnt recognize that as the broadcast for just the last subnet, and broadcast the entire network, not just the individual subnet. and the same thing with the network address .0 on the first subnet i guess. but apparently Cisco found a way around that? im not familiar with it.

 

Yes Cisco has found out a way and quite some time ago. Prior to IOS 12.0 the IP SUBNET ZERO command line could be used *IF* the network engineer saw it safe to do. Now, all Cisco IOS versions 12.0 and above come with IP SUBNET ZERO automatically enabled. You can turn it off by adding the line NO IP SUBNET ZERO.

Here is a Cisco link that will give you a little more info if you so desire.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml

 

hi friends thanks alot,

I really appreciate the reply and the efforts you all put to find out the solution ,but .........

I may not able to explain the exact scenario and the problem last time ....but any ways...

here is the atual problem.....


well you all says that a cisco router is required to connect two subnets ......AGREEE

but what if the two pcs that i took for the R&D is connected to a simple active HUB.Does hub is capable of communicating beetween two diffrent sunbnets?

Certainly NOT....!

and second thing you all said is .....took .32 as a first netwirk address and .33 as a first ip address ,

but still i able to ping successfully two diffrent subnets connected with hub


and did i forget something....?

NO i crosscheck the ip and subnetmask of both the pcs...

and both the pcs on diffrent subnet

main problem is not all but a few ip address range is pinging on diffrent network

As being a trainer ,I have a sound knowledge of subnetting
but one of student told me and bring my attention to this

is it possible that ip address design itself having problems?...who knows.....

but it subnetting is has its exceptions....

help me...

 

what? so youre saying you can ping each subnet when youre connected to a hub? that shouldnt be happening...at all. the most you should get, which it seems like you know, is a destination host unreachable. but i have class tomorrow so ill bring it up with my intructor to see if we can work out something. sounds like fun to see whats goin on.

if you could put down exactly what mask and ips youre using for the different computer and what kind of hub youre using, ill simulate it exactly tomorrow or whenever you get the time to reply to this. hopefully well come up with something, because now im curious.

 

thank you steveking

i am also a professional instructor one of my colleague's student give him the scenario and they successfully ping 2 pcs via hub.but the problem is the student already completed the course and we dont have his contact number .but im no more joking .

there are examples in which we could ping with diferent subnets.
and we cross checked every thing.the mask ,the ip address of both the pcs

and we are using simple hub of local manufactures

i will do my best to find out him and get the range that pings but now the matter is too curious for me.


if u have an answe in beetween just reply and reply fast

Thanking u alot


digital mafia

 

sorry man. i didnt realize you were the instructor i guess. theres probably nothing i could do that would get you an answer that you havent done or thought of already as im still a student. i know how to subnet but when it comes to troubleshooting stuff like that im clueless. im very interested though as to how thats working out, so if you do find an answer id like to know.