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Does Internet Explorer have a way to configure the MaxConnectionsPerServer settings when connecting through a proxy server (default appears to be 2)?

In Firefox there is a setting network.http.max-persistent-connections-per- proxy (which is currently defaulted to 4).

IE has various ways to configure connections but they do not seem to override the PROXY configuration

  • MaxConnectionsPerServer (HTTP 1.0)
  • MaxConnectionsPerServer (HTTP 1.1 - "per host")

Using some testing sites we can see these numbers changing with different browers on/off proxy (see browserscope.org and their network test):

IE11 (default settings) off proxy

  • Connections per Hostname = 13

IE11 through a proxy

  • Connections per Hostname = 2

There is rationale for these defaults but they seem to be increasing over the years (except for the Proxy side) ... see "Effect of Proxies"

Note that if you’re behind a proxy (at work, etc.) your download characteristics change. If web clients behind a proxy issued too many simulataneous requests an intelligent web server might interpret that as a DoS attack and block that IP address. Browser developers are aware of this issue and throttle back the number of open connections.

In Firefox the network.http.max-persistent-connections-per-proxy setting has a default value of 4. If you try the Max Connections test page while behind a proxy it loads painfully slowly opening no more than 4 connections at a time to download 180 images. IE8 drops back to 2 connections per server when it’s behind a proxy, so loading the Max Connections test page shows an upperbound of 60 open connections. Keep this in mind if you’re comparing notes with others – if you’re at home and they’re at work you might be seeing different behavior because of a proxy in the middle.

In particular I am investigating this due to IEs handling of connections when WebSockets are closed... frequent open/close events appear to queue up much faster in IE and the proxy max connections in the IE configuration appears to be to blame compared to other browsers.

felickz
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1 Answers1

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After many hours of testing and searching finally found a relatively hidden and undocumented blog post highlighting this configuration from the underlying WinINet API used by IE for HTTP communication: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings - MaxConnectionsPerProxy !

From 2009 (circa IE8):

While you could always change the number of connections WinInet (and Internet Explorer) used by default, in the past, you could not also control the number of Proxy Connections separately (also covered in RFC 2616). There is now a setting that will allow you to set the proxy connection limit independent from the number of persistent connections to a server.

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings

Value name: MaxConnectionsPerProxy

Value data: 2

Base: Decimal

We have seen IE with different behavior on a test site once changing this value!

See Also: WinInetOptionFlags for deeper details

felickz
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