> On Tue, Jun 11, 2013 at 09:43:07AM +0100, David Laight wrote: > > Is setting the mss to 536 actually ever sensible? > > RFC 879 might say that it is the default (and the minimum > > that must be supported), but in practise the actual mss > > is very likely to be only slightly shorter than the standard > > ethernet mss. > > Although strict conformance with RFC 879 might require the mss > > be clamped to 536, pragmatically a value much nearer 1400 would > > make sense - systems with very low mtu/mss are probably likely > > to advertise it. > > Read the associated bugzilla - there was at least one real world > example where setting a higher MSS was causing breakage. > > Phil > > https://bugzilla.netfilter.org/show_bug.cgi?id=662 To quote that bug: I stumbled upon this problem in debian bug #541658[1] ("[iceweasel] cannot open research.microsoft.com" - only worth reading for entertainment purposes) and, after that bug was closed, analysed it in my blog[2] until a friend of mine found out why the page loads when clamping mss to pmtu is disabled or restricted to a range (like with "iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1400:1536 -j TCPMSS --clamp-mss-to-pmtu") but doesn't load with "simple" clamping. His really great and detailed analysation of the problem may be seen at [3]. If I read/understand that correctly, clamping to 1400 worked - there was no need to clamp all the way down to 536. David -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
