Cisco Tunnel File Sharing Problems

Discussion in 'Cisco' started by Robert Jacobs, May 16, 2007.

  1. Hello!

    I have 2 Cisco 2801 series routers (one at our corporate office, and
    one at our branch location). I have setup a site to site vpn over an
    IPSec tunnel. The tunnel works perfectly fine in most ways. I can
    ping any address from either location at the other location. I can
    browse to any share on any computer. I can copy files that are
    approx. 3KB or smaller to PCs at the other location. I CANNOT,
    however, copy files larger than approx. 3KB. I get an error message
    after about 30 seconds that says "Cannot copy (name of file): The
    specified network name is no longer available." I can then take that
    exact file, remove enough information from it to take it below approx.
    3KB, copy the file again, and it finishes in no time flat. I am sure
    this is a result of the MTU fragmentation.

    Oh, the best part: This only happens on some computers. From certain
    computers, it doesn't matter what the size of the file being copied,
    it works perfect, other computers, it is extremely consistant. I have
    found a way to, on a PC by PC basis, resolve this issue (but would
    like a blanket resolution)...here's the resolution to fix one PC at a
    time: open regedit, navigate to HKEY_LOCAL_MACHINE\System
    \CurrentControlSet\Services\Tcpip\Parameters and create a new DWORD
    called EnablePMTUDiscovery and set the value to 0. Restart.

    Is there a way to get this same result by making a change to the
    router. I have tried these two things with no avail:

    Router# config t
    Router(config)# int tunnel0
    Router(config-if)# ip mtu 600

    &

    Router(config-if)# ip tcp adjust-mss 600

    Any Ideas?!?!?!? Thanks guys!
     
    Robert Jacobs, May 16, 2007
    #1
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