On Fri, Nov 03, 2006 at 09:17:47AM -0800, Tim Wilde wrote: > Chris Perry wrote: > > Thanks for elaborating. I suspect the MTU is not the issue at this > > time. I did have problems with the MTU when I started with DLS, and got > > that sorted, with assistance from the ISP. Today I was able to send a > > large email to the affected exim server without issue. The problem > > seems to centre on some relationship between the sending (UBS) and > > receiving servers. > > It could still be an MTU issue at their end, or a Path MTU Discovery > issue somewhere on the route between you and them. The symptoms you've > described definitely sound like MTU issues. Can you disable Path MTU > Discovery in your TCP stack? On FreeBSD you would do this by setting > the net.inet.tcp.path_mtu_discovery sysctl variable to 0. I've found > that this is a good way to find out if PMTUD is the problem or not - if > the problem messages come through successfully with PMTUD disabled, you > can further troubleshoot. It seems, though, that the problem may > actually be at the sending end of things, so you may need to try to get > them to disable PMTUD on their sending server and see if it works > better, which may be difficult to arrange.
another obvious thing to try is pings with different sized packets -- that won't give you a 100% reliable answer re TCP, but it might tell you something useful. You could also try a similar trick with tcptraceroute. -- ``As for Nitel, the state telephone monopoly, the less said the better, which might well be the company's motto.'' (The Economist, on Nigeria) -- ## List details at http://www.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://www.exim.org/eximwiki/
