Mailing List Archived Message #54

From: "Lewis G Rosenthal" <> Full Headers
Undecoded message
Subject: Re: [Virtualized eCS] TAP driver killing TCP/IP bandwidth
Date: Wed, 09 Dec 2009 18:28:29 -0500
To: Virtualized eCS Users Mailing List <>

Hi, Doug...

On 12/09/09 05:35 pm, Doug Bissett thus wrote :
On 2009-12-09, at 14:01:33, Lewis G Rosenthal wrote:
I'll have to fashion myself a CAT-6 crossover to eliminate the switch from the equation.)

Most modern switches, and NICs, will automatically reverse the wiring,
if they think you might be using the wrong cable. Just try a normal

Indeed, I thought of the auto-sensing circuitry, but don't know if the T43 or the new Intel chip (still trying to get GenMAC to work with it) - an 82567LF-2 - do auto-sense. The switch surely does, which is why I no longer stock crossover cables. :-)
Has anyone else seen this type of performance hit cuased by the TAP driver?

No, but my switch, and router, only run at 100 Mbs, so I may not have
noticed a speed reduction. I will see if I can hook it direct from my
desktop to my T43, and see what happens (may be tomorrow, before I get
a chance).
Thanks. I'm going to test on a couple other networks and systems available to me, as well. I, too, am normally sitting behind a 100Mbps secondary switch on this segment of the LAN or going wireless. However, the native B57 NDIS2 driver dropped off to under 500bps (that's bits, not Bytes!) vs GenMAC running the NDIS5 driver (without IJFW and IPX on the wire).

While this thread doesn't necessarily deal with virtualization per se, it is surely of impact to those of us using VBox as host, as it is a major pain to have to reboot just to get networking going in the guest session...


Lewis G Rosenthal, CNA, CLP, CLE
Rosenthal & Rosenthal, LLC      
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