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Hello,
Get a load of this, and please tell me what you think.
The MTU was originally set to 1500 on all machines. Most machines worked but
some
would not when posting large amounts of data.
When I set the MTU for all interfaces on the director to 1400 and leave the MTU
for
the tunnel untouched at 1500, all machines would fail.
When I set the MTU for all interfaces on the director to 1400 and set the MTU
for
the tunnel at 1400, all machines would fail.
With the MTU for the tunnel set to 1400. I can set the MTU for the director
to anywhere between 1420 - 1500 before it fails with all machines.
The largest packet I can transmit on the ISP's network without it fragmenting
is
1472 although they claim their MTU is 1500. (ping www.linux.org -l -f 1472
works
but anything bigger does not)
This makes no sense to me. The only way I can think this is correct is if:
Maximum packet size (without a tunnel) between director and real servers is
1500.
If the header for IPIP tunnel is about 20 bytes then the maximum packet size
for
packets within the tunnel is 1480.
Therefore, the MTU for the director must be at least 20 more than the MTU for
the tunnel.
So why does using 1400 everywhere make it all fail, but 1500 everywhere only
fail on
some machines?
What can I set the MTU values to in order to guarantee it working with all
clients? Most of our clients have no technical knowledge and this is becomming
a nightmare!
I would love to upgrade the Kernel (currently 2.4.20) but that is not an option
as a quick fix at the moment. - Live environment and the like.
Thanks in advance.
Chris
Berkeley Alexander
Temple House, 25-26 High Street, Lewes, East Sussex, BN7 2SD
Tel 01273 477784, Fax 01273 478994
www.baonline.co.uk
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