I was running dd-wrt 14144 on dir-615 c2 and it worked good but i found an instability problem with wireless connections... so i came back to d-link's 3.12NA firmware...
Well if you had no problems with D-Links official firmware in the first place then you probably had no need to go to DD-WRT. Like the saying always goes "If it's not broke don't fix it".
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I personally changed to DD-WRT due to some routing problems with multipul systems in my house. DD-WRT fixed it all for me. Also i've had no wireless problems on DD-WRT at all up to now. Everything i have wireless connects and stays connected. 99% perfect for me. Great speeds, more features etc etc. The only little niggle i had was the side light (I believe it's a reset button of some sort) is red on bootup of the router. A command in the Administration/command page fixed this for me.
Maybe in you case it was something to do with the hardware version being different but i have read reports of the D1 and D2 working fine. Your C2 hardware version may be the issue. I don't know for sure but maybe look around on DD-WRT's forums.
Good luck in whatever you go with
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