Wireless Adapter Seems Capped at 1300 MTU

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Carey

"Jim Yohn" <jyohn@mindspring.com> wrote in message
news:cq6vd.1765$2J2.564@newsread2.news.atl.earthlink.net...
> I'm running a Windows XP Pro desktop and I have a circumstance where the
> wireless connection is getting capped at 1300 MTU. Assuming wireless
> adapters are not supposed to be capped at 1300 MTU, I'd like to increase
> it to 1500 and improve transmissions.
>
> The other (wired) PC in my home network can get 1500 MTU, so I don't
> believe the local router is limiting it. I verified the wireless adapter's
> max MTU is 1300 by pinging the router/AP and external IP addresses with
> this command:
>
> ping <dest> -f -l 1272. where <dest> is any of the addresses I've tried.
>
> Any packet size higher than 1272 gets a response "Packet needs to be
> fragmented but DF set." With the 28 bits Windows tcp/ip adds for error
> checking, etc., 1272 + 28 = 1300 MTU.
>
> I have no MTU values set in the registry for the interface (or anywhere).
> I've tweaked tcp/ip settings with cablenut to optimize the
> transmit/receive window sizes (only after identifying the 1300 MTU cap).
> The wireless link to the router/AP is where the MTU limit appears to be in
> effect (the 1st hop).
>
> It is a US Robotic 5410 adapter connecting to a DSL modem via a USR 8054
> Router/AP. Any ideas for a way to increase the MTU using this adapter?
>
> Thanks,
> Jim
>
>