Wireless Adapter Seems Capped at 1300 MTU

Discussion in 'Wireless Networking' started by Jim Yohn, Dec 13, 2004.

  1. Jim Yohn

    Jim Yohn Guest

    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
     
    Jim Yohn, Dec 13, 2004
    #1
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    Carey

    "Jim Yohn" <> wrote in message
    news:cq6vd.1765$...
    > 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
    >
    >
     
    Carey Holzman, Dec 13, 2004
    #2
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