TCP and WAN issue

Robert Boyle robert at
Thu Mar 29 04:43:35 UTC 2007

A lot of different theoretical things have been discussed, but 
basically, if you are running Windows XP, 2000, or 2003 over a WAN 
with anything more than 10-20ms of latency, make the following change 
to the registry and you will find a world of difference. Ideally, you 
would make the change to both sides, but as long as one side has 
this, it will auto-negotiate with the other side to adjust the

Start, Run, regedt32

Go to:


Edit, New -> DWORD Value

Then name it "Tcp1323Opts" (without the quotes) and change the value to 3

That will give you far better performance by enabling automatic TCP 
window size scaling as per RFC 1323 over your WAN links (hence the 
key name), but only to other computers which support RFC1323. XP and 
2003 default to allowing scalable windows if the far side intiates 
the negotiation, but that will never happen unless one side has this key set.

Values are:
0 (disable RFC 1323 options) - default before creating the key
1 (window scale enabled only)
2 (timestamps enabled only)
3 (both options enabled)

Try this and let us know what you see.


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