Slow upload with 1 gig NIC, 100mbs NIC is fine

[peppy]

When i connect my PC directly to my fiber modem i get 75 mbps upload.

Then when i connect to same PC via my router the upload drops to 33 mbps !!

After struggling with this for 2 days i found out that forcing my PC nic to 100mbps the upload goes back to 75 mbps.

Are there any settings i can tweak so i can keep 1 gig lan and still get good upload speeds ?

Fixing lan at 100mbps hurts my download.

PS i got 100/100 mpbs fiber, modem :genexis core advanced with a 100mb wan port on a ASUS RT-N66U router.

 

[RMerlin]

I would replace the network cable you are using between the PC and the router. Chances are it's not rated for gigabit speed, so whenever data gets transferred, there are many packet retransmits due to errors.

Make sure the cable has "Cat 5e" or "Cat 6" written along its length. Older Cat 5 cables are not gigabit-capable.

Also disable Jumbo Frames if you had it enabled.