Server 2003 SP2: problema de rendimiento desde Vista en versión de 64 bits del servidor

Hay un fallo en la versión de 64 bits del SP2 de Server 2003 que hace que
una vez instalado y reiniciado el servidor, el acceso a los recursos del
mismo desde clientes con Windows Vista pasa a ser lentísimo. Esto sólo
afecta a clientes Vista (los XP y anteriores siguen funcionando
perfectamente), y sólo con las versiones de 64 bits de server 2003 SP2.

Mientras Microsoft saca una actualización que lo corrija, existe una
alternativa que consiste en deshabilitar dos funciones de red del nuevo
service pack (realmente ya existían en un complemento para SP1, pero no
era común encontrarlo instalado).
La "solución" temporal pasa por modificar dos valores del registro en el
servidor y reiniciarlo. Tras ello (lo he hecho con tres servidores 2003 de
64 bits y me ha funcionado perfectamente) el acceso de los clientes
Windows Vista vuelve a funcionar a la velocidad normal.

Las dos entradas a modificar en el registro del servidor, una vez
instalado en el mismo el SP2, son las siguientes:

Clave:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

DWORD EnableRSS = 0
DWORD DisableTaskOffload = 1

y reiniciar el servidor

A continuación pego el artículo completo tal como lo encontré en un foro
en inglés:

After installing Windows 2003 Service Pack 2 on SBS 2003 with ISA 2004
installed, you may experience the following problems:
-You can no longer successfully connect inbound using VPN (Clients get
"Error 800: Unable to establish connection").

-You cannot reliably connect to the Internet using SecureNat.

-Some Outlook clients will fail to connect to the Exchange server (even
with ISA 2004 SP2 and KB930414 installed).

(We are still discussing and testing other symptoms that could be related,
but if you are having networking issues after the service pack, consider
the solution provided on this post. We will update this list as we find
more factual information.)

There are several potential causes for these problems, but on this case,
we will focus on a feature called Receive Side Scaling that is enabled by
Windows Server 2003 SP2 (also enabled in the Microsoft Windows Server 2003
Scalable Networking Pack). Note that not all Network Cards will provide
this feature, also keep in mind that this might affect SBS machines using
RRAS for their NAT solution.

You cannot host Transmission Control Protocol (TCP) connections when
Receive Side Scaling is enabled, you have Microsoft Windows Server 2003
with Service Pack 2 (SP2) and you use Network Address Translation (NAT) on
the server. The TCP connections will be reset.

Update: The following KB explaining the behavior is now public:

KB 927695 "You cannot host TCP connections when Receive Side Scaling is
enabled in Windows Server 2003 with Service Pack 2"

You can disable this feature from the advanced properties of the network
card under the network interface properties or you can perform the
registry changes provided below.

You can disable the RSS support from the TCP/IP stack by doing the
following:
Warning Serious problems might occur if you modify the registry
incorrectly by using Registry Editor or by using another method. These
problems might require that you reinstall the operating system. Microsoft
cannot guarantee that these problems can be solved. Modify the registry at
your own risk.
To work around this problem, disable Receive Side Scaling when the
computer is configured as an Internet Connection Sharing gateway. To do
this, follow these steps:

1. Click Start, click Run, type regedit , and then click OK.

2. Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

3. On the Edit menu, point to New, click DWORD Value, and then type
EnableRSS .

4. Double-click EnableRSS, type 0 , and then click OK.

5. Exit Registry Editor.

If you are still experiencing problems (like slow file copying), you
should also disable Offloading support:
1. Click Start, click Run, type regedit, and then click OK.

2. Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

3. In the right pane, make sure that the DisableTaskOffload registry entry
exists. If this entry does not exist, follow these steps to add the entry:

a. On the Edit menu, point to New, and then click DWORD Value, and then
type DisableTaskOffload .

4. Double-Click DisableTaskOffload, type 1, and then click OK.

5. Exit Registry Editor.

(Reboot to make both changes effective)

Update 2:

We have seen several situations where even after completing the steps
above, VPN would still not work. On those cases, updating the NIC drivers
to the latest version resolved the problem. So, make sure you have the
latest version for your Network Card drivers. Most manufacturers have
released updated drivers very recently.

Saludos

José Antonio Quílez