No such problems here. Disabled second lan port in BIOS, only using the first now. I don't play D3 tho. Have no idea what could be wrong at your side.
I haven't tried turning off to be honest the second port in bios will try it cause tbh in my case is useless as well.For now I re-installed the latest driver but this time using Run as Admin and will test it for 2-3 days to see if it was simply a bad case of driver installation.Also changed the Link Speed from Configuration from auto-detect to manual speed of my lan to see if it helps.If doesn't i will also try disabling the second lan and i will report back.
Seems it was a bad install of driver 4 days now non stop rock solid network connection.If anyone has a similar problem Install latest Driver again with Run As Admin and and then change Link Speed from configuration of the network from auto detect to the manual speed of the lan that did the trick for me.
The problem reappeared on the today again.Disable/enable again fixedit instantly then i entered then bios and i did what you mentioned in the bios disabled the secondary lan. I need to confirm if your primary lan is the same as mine Intel 82579V?
Just wanted to mention I had this problem too, are you saying that I cannot be connected to two different networks at the same time? Because if this is true it's ridiculous, the other Ethernet port is not there purely for it's visual aesthetics.
For 2 weeks i had my mobo on the Secondary LAN Intel 82574 (since this was my Local Area Connection 1 automatically after format didn't know which one was primary and i assumed this one was) and i had this problem putting Manual Speed and reinstalling driver as admin made it to disconnect rarely but still disconnecting(from 1-2 days to 3-5 - but again fixing it was 5sec work but still annoying hiccup).Yesterday once i disconnected once again i did what dislikeyou did and disabled secondary LAN and reconnected to Intel(R) 82579V and so far seems OK i will for sure report back if everything worked OK for a bit longer but this smells like driver or bios problem rather than hardware.
PS.Anyone from the intel staff if they can acknowledge this as known issue of driver/bios would be good (we have long patience 
as long as we hear some confirmation of an issue/bug or even they are looking into it cause the mobo is rock solid and performs excellent its bad to have and little but annoying problem).
cpu:i7- 3770k,mobo=DZ77GA-70K,Bios:045,Lan Driver:17.1,Router:Thomson 585v7.
Same issues here. However I can´t fix it just by disabling that NIC and enabling it again. After trying that several times the Systems freezese completely. Only a restart fixes it but just for a couple of hours in the best case.
For now a made an ALB-Group of both NICs to ensure that I don´t get kicked out of RDP-Session and other Online-Activities.
i5-3570k, DZ77GA, BIOS: 049, LAN-Driver: 17.1 x64 on Win7 x64
exactly same issue, bios 0049 already installed is there any fix?
same issue, but i fixed it by disable the second lan port in BIOS.
