Why when i installed TMG i became disconnect and connect from internal network to TMG and external

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http://serverfault.com – when i install tmg server 2010 on windows server 2008 R2,after some minute i have request time out in ping of internet and ping of ip addreess of tmg server and i became disconnect from tmg and after some minute i connected at it.. this is things i do for installing tmg 1.set ip address on 2 NIC thet LAN NIC dont have getway and have DC ip address as a DNS and WAN NIC have ip address and getway and DNS= 2.i have ping of internet and internal network all of the time on tmg server 3.install prerequirment of tmg server 4.add access role for connectivity of LAN and Local host by this action (HowTos)