What is an MTU and why is it important?

Question on MTU settings in a router?

• hi we have dlink router in our home,to which there were four systems connected..the MTU settings is set to 1500MTU....please clarfiy what exactly is MTU for?.... per my understanding,its the maximum packets of information tranferred over the network...is that right? so, if four systems are connected to the router, does that mean only around 1500/4 = 375 is available for each of the system....because,am trying to use XBOX with one of 4 conncetions, and the xbox fails the MTU test saying,it doesnt have sufficient MTU ...so please help me fix this

• Answer:

  No MTU is the "maximum transmit unit". It's the maximum number of bytes the router will send in a single packet. It is a parameter for the link between your router and your ISP. My bet is your XBox is failing the MTU test because the server it tests against is down and not because anything is wrong with your network. If your Xbox just started failing the MTU test and you didn't change anything, then that's the reason. If your network has had this problem for several days and has never passed the MTU test, then it's possible you have an MTU problem. You should set your router's MTU to your ISP's recommended MTU. This is 1500 for most ISPs. Some use PPPoE though, and recommend a slightly smaller MTU. Try 1364. This is the *lowest* MTU that Xbox live supports. If setting the MTU to 1364 solves the problem, you should check with your ISP to find the largest MTU that will work (since lower MTUs hurt performance). It's typically 1490 or 1492. Essentially, the problem is either that Xbox live is down or that your router is set for a higher MTU than your ISP supports.