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I have a Linksys router (WAN = cable modem) connected to a Linksys gigabit switch in addition to a Linksys Wireless G router.

My XBOX 360 is connected via CAT6 to either the router or the switch - I forget which one and my cables are so crazy underneath my desk it's too much of a mess to trace it to figure it out.

My network has always worked just fine. However, when I have the router's MTU set to Auto, my Xbox can't connect to the Internet. It's only when I set my router's MTU to Manual (1500 bytes) that suddenly my Xbox can get Internet access.

There's no problem in doing this. I'm just wondering why this is. I'm assuming (and I am probably wrong) that the Xbox is trying to transfer packets that are larger than whatever the router's default MTU size is? Wouldn't they just get divided into smaller packets en route? And isn't 1500 bytes standard, anyways, so shouldn't that be what the router's default setting is? I'm confused.

I'm having the EXACT same problem with my Motorola WR850G cable Router. Network runs great but occasional MTU failures on the Xbox. Appears that I don't have a 'manual' mode to switch the MTU which is how I discovered your post - searching for a solution to this MTU nuisance. Hopefully I'll be hearing from Motorola on how to switch the MTU when the router's in 'cable' mode soon.

I have a Linksys router (WAN = cable modem) connected to a Linksys gigabit switch in addition to a Linksys Wireless G router.

My XBOX 360 is connected via CAT6 to either the router or the switch - I forget which one and my cables are so crazy underneath my desk it's too much of a mess to trace it to figure it out.

My network has always worked just fine. However, when I have the router's MTU set to Auto, my Xbox can't connect to the Internet. It's only when I set my router's MTU to Manual (1500 bytes) that suddenly my Xbox can get Internet access.

There's no problem in doing this. I'm just wondering why this is. I'm assuming (and I am probably wrong) that the Xbox is trying to transfer packets that are larger than whatever the router's default MTU size is? Wouldn't they just get divided into smaller packets en route? And isn't 1500 bytes standard, anyways, so shouldn't that be what the router's default setting is? I'm confused.

I suspect that your linksys 'switch' is sending 1500 packets by default, and many newer routers, both cable and ADSL2+ use PPoE or PPoA, which has a packet size of 1492 by default, so your assumption is most likely correct!

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