Multiplayer bullet damages

Hello !

I'm starting Unity and to begin i would like to create a little shooter.
Everything is working fine except the bullets, when they collide nothing happen.
I did a check on the playerController if oncollisionenter the tag is weapon bam it call a function that reduce the health :

Code (CSharp):

1.  
2.   [Command]
3.     public void CmdReiceveDamages(int amount)
4.     {
5.         currentHealth -= amount;
6.     }
7.  

I dont get what's wrong, when it collide this function tell to the server hey i'm touched !

Code (CSharp):

1.     public void OnCollisionEnter(Collision collision)
2.     {
3.         if (isJump)
4.         {
5.             isJump = false;
6.             audio.PlayOneShot(sounds[3]);
7.         }
8.         if (collision.collider.tag == "bullet")
9.         playerHealth.CmdReiceveDamages(20);   //The function called to reduce health
10.     }

Anyone have any idea ?