Tech Help: MTU Settings

[SweetMommy]

So Xbox Live is all of a sudden telling me i need to change my MTU to a higher number...............HOW THE HELL DO I DO THAT????? I have COmcast and a Motorola SBV5220 Cable Modem. any other info just ask.

 

[FireDancer]

Do you have a router in addition to the cable modem? If so that is where you would set the MTU.

ETA: It looks from a little research that Comcast sets their MTU size very low. I also can't find a manual for that modem but you should be able to connect to it via the admin page (just point your web browser at it's IP address which is probably 192.168.100.1) and see if there is a setting. If you or Comcast hasn't changed it your default user name and password should be admin and motorola.

Many ISP provided modems and routers are restricted in what you can do to them so if you don't have a separate router you might want to get one. You can get a Linksys for under $40 now.

 

[SweetMommy]

I did not change it but those are not the right username and password settings any other ideas by chance???



Thanks for your help


Edit: I found the username and password defaults


How do i change the MTU???

 

[FireDancer]

I did not change it but those are not the right username and password settings any other ideas by chance???



Thanks for your help


Edit: I found the username and password defaults


How do i change the MTU???

I'm really not sure because I have never used that modem and I can't find a manual online. It is very possible that you can't change the MTU in that modem because Comcast doesn't want you to. All I could suggest is poking around the menus, especially anything labeled LAN administration or an equivalent, and see if you can see a setting.

Comcast does purposely lower the MTU from the ethernet standard, which is more than large enough for the XBox, which leads me to believe that you will be stuck having to purchase another router to use the XBox. Almost any 3rd party router will not have to have the MTU changed as the ethernet standard is find for the XBox, even over wireless.

Sorry I can't help you further but this is pretty standard for Comcast and, in fairness, other service providers, equipment and why I recommend installing your own router behind the ISP's modem.

 

[BunsenH]

I don't have a solution, but am curious about one point.

If the MTU of the modem is restricted, how would putting a router in series between the modem and Xbox improve the situation? Doesn't the MTU of the modem still 'throttle' the throughput?

 

[FireDancer]

I don't have a solution, but am curious about one point.

If the MTU of the modem is restricted, how would putting a router in series between the modem and Xbox improve the situation? Doesn't the MTU of the modem still 'throttle' the throughput?

The MTU size on the LAN (Ethernet) side of almost any router will be higher than the WAN side. The issue in this case isn't the total throughput, which is limited by the speed of the connection, but the size of the individual packets being broadcast. In simple terms the packets coming in from the WAN will be repackaged into larger packages (MTUs) for broadcast over the LAN. All the XBox will see is the MTU size on your side of the router, not the ISP facing side, so it will cease to give you the error. It may not help on a throughput case but it will let you hook it up. While a higher MTU from the ISP would be beneficial in certain areas, like streaming large content like movies, it also makes it harder for them to manage their network. Lets not also forget that Comcast wants you to buy content from them so making their network less hospitable to streaming media, which a lower MTU does do, kind of helps them without being obvious throttling.

You will almost never be able to change the incoming MTU size from the ISP as that is controlled on their end but you should be able to change that size on your own LAN.

 

[BunsenH]

Thanks for the tutorial FD.

Kudos on the 7K posts (that's 7000 not 7168!).