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Read a lot discussions 'bout the topic and still I can't manage to achieve higher speeds. PassMark Advanced network test shows around 270Mbit max via TCP, in both ways, UDP is around 520Mbit, but my focus is on TCP

---- 1box: Win7 sp1, GA-MA78GM-S2H, card: onboard Realtek PCIe GBE, jumbo frames set at@9k(max), newest lan driver(2011) and reg.TcpWindowSize tweak (@131400)


---- switch TP-Link SG10008D (with jumbo frames support @16k)


---- 2box:WinXP sp3, Atom d410pt, card:TP-Link TG-3269, jumbo frames set at@7k(max), newest lan driver (2011) and reg.TcpWindowSize tweak (@131400)

switch and 2box tp-link card are Automatic MDI/MDIX (don't sure 'bout 1box onboard Realtek but it's suppose to be) and all cables are cat5e, auto-negotiation shows connection 1Gb/s estabilished also hard drives are benchmarking@85MB/s so...

NICs options:

  • QoS disabled
  • LargeSend Offload: enable
  • FlowControl: disabled
  • GreenEthernet: enabled

there's no effect even messing around with those above (!QoS)

but when I

ping -f -l 5122 next_box_IPaddr (in fact any value >1492) i've got "Packet needs to be fragmented but DF set." so is that in fact shows no Jumbo Frames not working properly in OS?

have anyone got any ideas os this is a result of my misunderstanding.

Appreciate your help.

share|improve this question
If you don't mess around with jumbo frames at all what speed are you getting? Even cheap gig nics should be able to do that. Did you check the CPU/memory usage on your test boxes? Not sure about passmark, but I have seen some network tests max out the CPU on older hardware. –  Zoredache Oct 19 '11 at 21:24
@Zoredache that's odd because I had Jumbo frames disabled by default on 1box & 2box NICs configurations by default and enabling them didn't increased speed a lot, simultanously I made some tweaks via TCP Optimizer, which also left me with no gigantic improvement. Also disabling OS firewalls : no changes. Am I suppose to manually change MTU (via TCPoptimizer) to around 8192? (as I've seen some advice on that, but-a...)... I thnik all of this shouldn't be that way all. –  xymox Oct 20 '11 at 6:47
Also CPU is about 7% on 1box and 60% on box2 usage during speed test . –  xymox Oct 20 '11 at 6:59
Jumbo frames does not dramatically change the speed at all, it really won't change it at all. It mostly just cuts down on the CPU overhead, and the overhead of the protocol headers. –  Zoredache Oct 20 '11 at 7:48

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