Nigel Metheringham edited this page Nov 29, 2012 · 2 revisions

Q0068

Question

Exim times out when trying to connect to some hosts, though those hosts are known to be up and running. What's the problem?

Answer

There could be a number of reasons for this (see also `../Q0017`_). The obvious one is that there is a networking problem between the hosts. If you can ping between the hosts or connect in other ways, the problem might be caused by ECN (Explicit Congestion Notification) being enabled in your kernel. ECN uses TCP flags originally assigned to TOS - it's a "new" invention, and some hosts and routers are known to be confused if a client uses it. If you are running Linux, you can turn ECN off by running this command:

/bin/echo "0" > /proc/sys/net/ipv4/tcp_ecn

This has also been reported to cure web connection problems from Mozilla and Netscape browsers in Linux when there were no problems with Windows Netscape browsers.


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