Dear All, Within our company we have some inhouse developed applications which communicate over the loopback adapter when resided on the same box. This raised the question if methods like Nagle and TCP delayed acks also apply to such adapters, as it is still tcp communication. I found in the MSDN Library that Nagle is not applied to loopback adapters. Is this also the case for TCP delayed acks? The relevant article in the MSDN Library does not mentions anything about how loopback adapters are treated. So far I only found some articles on the Internet which discuss TCP delayed acks and loopback adapters for unix and linux systems. Here the articles from MSDN NAGLE http://msdn.microsoft.com/en-us/library/ms817942.aspx TCP Delayed ACKS http://msdn.microsoft.com/en-us/library/aa505957.aspx I hope somebody can provide a answer to this. Thank you. With Regards, Wim

How does DelayedACKs matter with loopback adapter in picture? In any case, here is the registry key to control the delayed Ack on a per interface basis. http://support.microsoft.com/kb/328890 Sumesh P - Microsoft Online Community Support

Hi Sumesh, Thank you for your input. Well as explained we have processes communicating using TCP sockest over the loopback interface. And this is still TCP communication where also methods like nagle and delayed acks can apply. My search on the internet already gave me info that disabling delayed acks or nagle on the loopback interface will speed up inter process communicating, when applicable. This depends on your os and version. For example OpenBsd has disabled delayed acks on loopback in their releases after version 4.8 for example. (disabling delayed acks also effectively disables nagle) http://openbsd.das.ufsc.br/plus.html For Windows OS I can only find that nagle is disabled on loopback adapters in the MSDN library. But delayed acks may still apply then as the MSDN library does not give this information for delayed acks. About the link, I am already familiar with the registry change. Unfortunatley the default loopback adapter does not turn up as an network adapter in your registry. Only manually installed loopbacks will turn up in the registry. (Under 2008 they even made a clear distinction between the 2, software loopback interface vs Microsoft Loopback adapter) The Microsoft Loopback adapter can be found back under [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkCards] and its respective GUID under [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip\Parameters\Interfaces] So these are configurable but noot the default software loopback interface. Thanks.

Hi Sumesh, Thank you for providing the answer.