On Tue, October 14, 2008 12:31, Kai Schaetzl wrote: > Ralph Angenendt wrote on Tue, 14 Oct 2008 17:24:08 +0200: > >> If you don't know the smallest MTU on the path to the mail server, you >> might not be able to send packets over that path, especially if DF is >> set. > > But if it's not set? Shouldn't most devices have it not set? Yes, most devices should fragment if necessary (DF not set). Most devices should also pass/accept ICMP messages relating to their connections. Deliberately configuring them not to is asking for trouble; those messages are part of the protocol for a reason. (Fragmentation introduces more work and effectively many more lost packets in most setups, so the flow will be jumpy and less efficient even if it mostly works.) -- David Dyer-Bennet, dd-b at dd-b.net; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info