Hi Alaa
do u wanna set static mac or static arp ?
if you wanna set static mac you should deploy your firewall as transparent mode.
you can refer to this KB
http://kb.juniper.net/index?page=content&id=KB6120&actp=search&searchid=1251048406434
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The 'set MAC' command sets a static MAC address per interface to the MAC learning table of the Juniper Firewall NetScreen device. This command is only available on NetScreen devices in transparent mode. If the NetScreen is in NAT or Route mode, the 'set MAC' command will not take any effect. There is no way to change the MAC address of the physical interface itself.
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but if you wanna set static arp, this command like below
set arp <IP address> <Mac> <interface>
Thanks
EL