file shares not accessible via vpn because of MTU size

Discussion in 'Windows Networking' started by sumGirl, Mar 2, 2007.

  1. sumGirl

    sumGirl Guest

    Hi all! I had a weird problem this week where I could connect to one
    of my office's VPN concentrators and work just fine no problems, but
    if I connected to another concentrator in a different office then I
    could not browse file shares. We noticed lots of kerberos messages in
    a trace via the bad connection, but we could ping all the servers we
    could browse or map to (with both IP and resolved names). It wasnt
    WINS related either, we ruled that out quick.

    We actually founf that if we changed the MTU on the client side then
    the problem went away. Can someone just help me understand how that
    might work? I am guessing that the connection to the "good vpn
    concentrator" somehow allowed for a larger MTU awhile the patch to the
    "bad concentrator" did not?

    Please educate!
    sumGirl, Mar 2, 2007
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  2. You get into "fragmentation" issues with MTU sizes and devices that can't handle
    whatever the size might be set to. MTU is a "size" setting and if something is
    too big to transfer by the device trying to transfer it, then it has to be
    broken into smaller parts (fragmented). I believe it is usually the VPN
    Servers/Routers (concentrators) that are the failure points. The MTU should be
    set to whatever the hardware "likes" (whatever that may be) and the
    devices/clients should probably "agree" on what that setting should be.

    That is the only way I know to view it anyway. I have not had it happen to be
    so I don't have any practical experience with that issue.

    Phillip Windell [MCP, MVP, CCNA]

    The views expressed (as annoying as they are, and as stupid as they sound), are
    my own and not those of my employer, or Microsoft, or anyone else associated
    with me, including my cats.
    Phillip Windell, Mar 2, 2007
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