Very common problem here in Pattaya is the inability for users to view certain sites, in particular Live (Hotmail), Yahoo and Ebay. Quite often this is the result of an MTU problem.

What is MTU? MTU is a Maximum Transmission Unit, which is the greatest amount of data that can be transferred in one physical frame on the network. In plain English, when your PC requests data from these sites, they use something called Path MTU Discovery to check what size packets to send back to your PC. If the site is unable to check what size packet to send it uses the default MTU of 1500. This is a largest packet size, but in a reality in Pattaya or Phuket, there are certain gateways and routers on the Internet which use a smaller MTU, therefore the packets are too large to be transmitted and are rejected or dropped.

It is the job of Path MTU Discovery to find and report the smallest MTU setting between your PC and the remote site, so that the remote server sends out the correct sized packets. Large packet sizes will have to be fragmented.

What can I do to correct this?

You need to lower your MTU settings in your ADSL router and make sure that packets could be sent without fragmenting.

How to tweak your router?

Many routers have a setting in which you can change MTU size. You can change this, but you must make sure that the MTU setting on your router is the same as on your PC. It does not matter too much if the MTU on your router is higher than that on your PC, but the setting in your router must not be less than the MTU on your PC.

To determine your ISP MTU size, you need to ping it with different sets of MTU packets. A series of ping tests using the command, ping www.totisp.net -f -l xxxx, where xxxx is the packet size, can be used to determine the optimal MTU for your connection.

On Windows PC, go to Start and select Run.

Type in "cmd", hit the enter key or click OK. The DOS prompt should open.
At the DOS prompt, type in ping www.totisp.net -f -l 1492 and hit the Enter key

Note the results above indicate that the packet needs to be fragmented. Lower the size the packet in increments of +/-10 (e.g. 1472, 1462, 1440, 1400) until you have a packet size that does not fragment.You will need to set up highest unfragmented MTU size in your router and PC.