On Thursday, 2002-10-10 at 00:55 ZE2, Iljitsch van Beijnum <iljitsch@muada.com> wrote:
You can also get around this by making the first hop the one with the lowest MTU. This is no fun for ethernet-connected stuff, but for dial-up this is easy. Then this box will announce a smaller TCP MSS when the connection is established and there aren't any problems.
Traffic consists of more than tcp; setting your mtu low might get your tcp traffic delivered but won't help inbound traffic using other protocols. Mtu discrepancies must be dealt with in at least one of the following ways if you don't want it to lead to fatally dropped packets: 1. Fragmentation must work. This applies to systems that don't use PMTUD or use blackhole detection. (Some folks think it a good "security" practice to drop fragments! Some nat boxes don't know what to do with fragments when they arrive out of order - especially a non-initial fragment before the first.) 2. PMTUD must work. 3. PMTUD blackhole detection must be used with operable fragmentation. (If you have to fallback to this you're likely to suffer significant performance hits.) Tony Rall