iBurst – Vista and MTU settings
by computerwiz on Feb.23, 2009, under Computer Wiz - Blog
iBurst requires that your MTU be set to a size of 1352 on your operating system namely Windows XP or if using Vista unless you are using an Apple Mac in which case it must also be set.
Do not forget that the MTU must be set on your router and Linux machine if you are using additional equipment on your network.
Before being able to explain MTU it helps if we have a basic understanding of how data is transmitted.
Networks use certain protocols to send and receive data.
TCP or Transmission Control Protocol is one of the core protocols in the Internet suite as it provides a means of reliably sending data between two connections.
How its able to guarantee a reliable connection is through its use of acknowledgements or ACK from the receiving system.
When someone sends you data this is broken up into small packets the host will send a packet of data which then requires an acknowledgement from the receiving system.
Once the sender has received an ACK it will continue to send the next packet of data. If for any reason an ACK is not received the host will wait for a short period of time before trying to retransmit.
This constant chatter of stop and start between the 2 connections ensures that all packets are received in the correct order.
Maximum Transmission Unit or MTU
The MTU is the maximum amount of data (packet size) that can be transmitted in one go before it has to be cut up into smaller chunks. Each network has a maximum limit of data size it can cope with before data is fragmented into smaller packets. This figure may vary from network to network.
If you are using your iBurst Broadband connection to establish VPN connections then you must set the MTU size to 1324.
Vista needs to have the MTU set to 1352 when using iBurst and the following commands could be used in combination with a batch file that could be enabled or run after the iBurst connection has been made.
The following command could be used to disable the automatic MTU function within Vista.
Click start
Find command prompt
Right-click command prompt and click Run As Administrator
Type: netsh int tcp set global autotuninglevel=disabled
Press enter
Now run your batch file and observe your MTU settings.
The commands displayed below must be used in your batch file.
netsh interface ipv4 set subinterface “iburst” mtu=1352 store=persistent
netsh interface ipv4 show subinterfaces
The above has been tried and tested with great success on a Vista machine.
Webpages load correctly and are fully displayed.
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