On 2008-10-14 16:31, Kai Schaetzl wrote: > Sean Carolan wrote on Tue, 14 Oct 2008 08:13:34 -0500: > >> My mail logs are showing that customers who specifically disallow ICMP >> traffic have many "Connection Reset" entries in our logs: > > Could somebody explain why ICMP might play a role in mail delivery? Any host may reply to a IP-datagram (tcp included) with e.g. ICMP type 3, code 4 "datagram too large" and indicating the maximum size in the ICMP reply. Disallowing these ICMP packets can result in a TCP handshake that succeeds, but hangs when the next packets with real data are blocked. http://en.wikipedia.org/wiki/PMTUD -- Paul Bijnens, xplanation Technology Services Tel +32 16 397.511 Technologielaan 21 bus 2, B-3001 Leuven, BELGIUM Fax +32 16 397.512 http://www.xplanation.com/ email: Paul.Bijnens at xplanation.com *********************************************************************** * I think I've got the hang of it now: exit, ^D, ^C, ^\, ^Z, ^Q, ^^, * * F6, quit, ZZ, :q, :q!, M-Z, ^X^C, logoff, logout, close, bye, /bye, * * stop, end, F3, ~., ^]c, +++ ATH, disconnect, halt, abort, hangup, * * PF4, F20, ^X^X, :D::D, KJOB, F14-f-e, F8-e, kill -1 $$, shutdown, * * init 0, kill -9 1, Alt-F4, Ctrl-Alt-Del, AltGr-NumLock, Stop-A, ... * * ... "Are you sure?" ... YES ... Phew ... I'm out * ***********************************************************************