I've had the GA-970A-D3 board replaced with a GA-990FXA-D3 and everything is working fine. The network adapter specs are still the same.
Either it was a dodgy board or the BIOS just couldn't handle SL6.4

Regards
Bill Maidment
Maidment Enterprises Pty Ltd

N.B. Any email disclaimer in the original message has been carefully ignored as it has no meaning in law.
 
 
-----Original message-----
> From:Konstantin Olchanski <[log in to unmask]>
> Sent: Tuesday 7th May 2013 8:59
> To: Bill Maidment <[log in to unmask]>
> Cc: [log in to unmask]
> Subject: Re: Netrwork dropping transmitted packages on fresh SL 6.4 install
> 
> On Sat, May 04, 2013 at 06:11:21PM +1000, Bill Maidment wrote:
> >
> > GA-970A-D3 motherboard ...
> > SL 6.4 64 bit ...
> > Realtek RTL8168/8111 ethernet ...
> > 
> 
> I have seen problems with Realtek GigE ethernet, too. Under some loads
> it would just stop. (revivable by "ifconfig down"/"ifconfig up").
> 
> Switching to ELREPO realtek drivers fixed this problem. YMMV.
> 
> "Konstantin recommends ASUS motherboards with Intel GigE ethernet"
> 
> -- 
> Konstantin Olchanski
> Data Acquisition Systems: The Bytes Must Flow!
> Email: olchansk-at-triumf-dot-ca
> Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3, Canada
> 
>