Red Hat Enterprise Linux 5.5 DHCPv6 server may not interoperate with SuSE Linux Enterprise Server 11 (SLES 11) client

Issue

• I have setup one IPv6 DHCP server for Red Hat Enterprise Linux 5.5 but my client cannot get ipv6 ip address from the server.
• I have 4 DHCP clients but only 2 client can obtain IPv6 address. 
  • client 1: Windows7  (pass)
  • client 2: RHEL5.5 64bit (pass)
  • client 3: SLES11 SP1 cannot get ip address
  • client 4: The IP of server management(BMC) cannot get from DHCPv6 server