How to relese/renew ip

Hi All,

I want to know how i can release ip address provided by one dhcp server .The dhcp client and dhcp server both  
running on redhat linux.
  And how I can renew the ip address  from dhcp client assigend by dhcp server (the client and server both running on redhat linux).

Please help me.
Thanks and regards,
Somenath




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