New IT professionals may think that adding a second network card will improve throughput. While this can be true, IT personnel need to be aware of several rules behind configuring multiple network cards.
Assuming the server will be in the same subnet, once the network cards are installed, several decisions have to be made. Will the cards be independent and have separate IP addresses or will the cards be bridged and have the same IP address?
Two IP addresses
If you plan on installing two nic cards in your server and you want to use two ip addresses-
- Make sure that licensing of software is not based on the MAC address of one of the NIC cards
- Do NOT enable NetBIOS over TCP/IP – This can cause the name of the server to appear on the network more than once and an error will occur (multiple NetBT Event ID 4319 Errors stating “A duplicate name has been detected on the TCP network)
- Use an internal DNS server – Client computers will use a DNS round-robin and routing tables will be built
One IP Address, multiple NIC cards
If you plan on using aggregation or the bridging of your network cards-
- USE HP, Intel, Broadcom or other NICs that support teaming (drivers) – this is important so that the cards will be used together
Note- (Our recommendations)
- Connect each NIC to a separate switch to ensure switchport flooding does not occur.” Use switches that support IEEE 802.3ad
- USE RSS and modify the registry appropriately to use multiple CPUs
In Windows Server 2008, administrators can set the maximum number of RSS CPUs with the MaxNumRssCpus registry keyword in HKEY_LOCAL_MACHINE\\SYSTEM\CurrentControlSet\Services\Ndis\Parameters. TheMaxNumRssCpus value is a DWORD type and, if it is not present, NDIS uses the default value of 4.
More information: http://msdn.microsoft.com/en-us/library/windows/hardware/ff570795(v=vs.85).aspx
- To enable RSS:
- Open a command prompt as an administrator
- Type the following command, and then press ENTER:
netsh int tcp set global rss=enabled
- You may want to also enable TCP Chimney if your NIC card supports it. http://support.microsoft.com/kb/951037
Is TCP Chimney working? Type netstat -t if you see Offloaded during a connection, this feature is working
An excellent article on the use of multiple NIC cards http://blogs.technet.com/b/josebda/archive/2010/09/03/using-the-multiple-nics-of-your-file-server-running-windows-server-2008-and-2008-r2.aspx