Change the MTU under Vista or Windows 7

First of all you are going to need to find the optimum mtu for your situation to do so follow these instructions.

ping www.google.com -f -l 1500 (lower case F and L not a 1)

you will receive something similar to this.

Pinging www.l.google.com [66.102.9.105] with 1500 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 66.102.9.105:
Packets:Sent = 4,Received = 0,Lost = 4 (100% loss),

Now you need to drop the packet size down by 10 bytes until you find one that doesn’t fragment in this case it was dead on 1430 but you can increase the byte size by small factors eg 1431,1432 etc until you find that largest possible packet for your situation.

Pinging www.l.google.com [66.102.9.103] with 1430 bytes of data:
Reply from 66.102.9.103:bytes=64 (sent 1430) time=100ms TTL=54
Reply from 66.102.9.103:bytes=64 (sent 1430) time=70ms TTL=54
Reply from 66.102.9.103:bytes=64 (sent 1430) time=64ms TTL=54
Reply from 66.102.9.103:bytes=64 (sent 1430) time=64ms TTL=54

Ping statistics for 66.102.9.103:
Packets:Sent = 4,Received = 4,Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 64ms,Maximum = 100ms,Average = 74ms

Now you need to add 28 to the maximum size for the overhead the IP headser and the ICMP Echo Request, so I end up with 1430+28=1458 then you need to change the MTU to do so.

1. start an elevated cmd prompt
2. type netsh interface ipv4 show subinterfaces (this will show you the existing mtu and network adptor name)
3. type netsh interface ipv4 set subinterface “Local Area Connection” mtu=1458 store=persistent

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