Hi guys.
IP addressing on R10&R8 and R8&R11 is strongly correct, but why am I receiving neighbor not on common subnet error on R8,R10 and R11??
notice that I'm using EIGRP and the AS number for all router is 70.

Without your configs, how do you expect anyone to tell what you problem is???????????? BY MAGIC???

So try this magic.

You have the IP addresses of S0/1 and S0/2 on R8 swapped around.

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RedNectar
http://rednectar.net
@rednectarchris
GNS3 WorkBench-a VMware image of Ubuntu with GNS3 and VPCS installed and a collection of exercises/labs

Stay calm dear friend, I'm gonna to do it. :)
The Configs are as follow:
Notice that, I've not configured any feature except simple EIGRP.
thanks.

From your topology picture: R8 s0/1 is connected to R10 s0/0, and IP addresses configured are: 90.0.0.1/8 on R8 and 90.0.0.2 on R10. It is good, but... on R8 you have message about serial 0/2 (!)

Also, from topology piture: R8 s0/2 is connected to R11 s0/0, and IP addresses configured are: 100.0.0.1/8 on R8 and 100.0.0.2 on R11. It is good, but... on R8 you have message about serial 0/1 (!)

Looks like you connected R10 s0/0 to R8 s0/2 instead to R8 s0/1. And R11 should have been connected to R8 s0/2, whlie you connected that to R8 s0/1.

You can do "sh cdp neighbors" on R8 and check if I'm right. Reconnect R10 and R11 to R8 properly, it should fix your problem. Alternatively, you can change R8 IP addresses on s0/1 and s0/2 (like rednectar said)...

BTW:
instead of making screenshots and attaching to your post, it would be MUCH better to attach ZIP file of your project directory. That case look simple, but with more sophisticated topology it takes MUCH time to us to recreate your topology. You want us to help you, so PLEASE: save OUR time...

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If you can see any inaccuracies or other language-related mistakes in my post(s), please forgive me - English is not my native language

Abort has nailed it. You have to be very careful about what your diagram APPEARS to show and what the connection configuration really is, because the labels S0/0 etc are simply that - LABELS - they don't necessarily move when you move devices around.

SO although your diagram SEEMS to show that R8 S0/1 is connected to R10 S0/0, in actual fact R8 S0/1 is connected to R9 S0/0. You can see this in your topology if you go to the GNS3 Command console and issue a show run command.



Illustration taken from theGNS3 Network Simulation Guide:

Disclaimer: I am the author of theGNS3 Network Simulation Guide

_________________
RedNectar
http://rednectar.net
@rednectarchris
GNS3 WorkBench-a VMware image of Ubuntu with GNS3 and VPCS installed and a collection of exercises/labs

Thanks rednectar :)
I was focused on Labels instead of Topology Summary and that's my fault.
as other guys said, IP addressing was incorrect because of incorrect labels.