2 cents re: MTU

Jamie Erbes (jamie@erbes.com)
Wed, 24 Jun 1998 23:51:53 -0700

MTU - Max transmission unit - default from windows is 1500 which is good for LAN but typically not so good for analog dial-up. The objective is to match the setting of your ISP, which is usually 576. You may need to call your ISP to see what their MTU is for your access type.

MSS - Max Segment Size - Windows adjusts this automatically according to your MTU.

RWIN - Receive window - I've seen Windows default to 8192, which, again, is OK for LAN but not so good for analog dial-up. A good rule of thumb is to set RWIN at 4X your MSS. Then round it to a number divisible by 32 for further optimization.

So if your ISP sets MTU at 576, you should change yours to match. Then subtract 40 for your MSS value of 536 (but don't set it because Windows will take care of it for you). Multiply 536 by 4 for 2144 and round it to 2048 for your RWIN setting.

General guidelines - as someone commonly writes in this list: "Mileage will vary"

Jamie Erbes - jamie@erbes.com
Erbes Development Group, Inc.