On Sun, Oct 27, 2013 at 08:14:19PM +0100, Jozsef Kadlecsik wrote: > On Sun, 27 Oct 2013, Patrick McHardy wrote: > > > On Sun, Oct 27, 2013 at 06:01:30PM +0000, Patrick McHardy wrote: > > > On Sun, Oct 27, 2013 at 08:34:09AM -0700, Phil Oester wrote: > > > > On Sun, Oct 27, 2013 at 12:14:48AM +0400, WGH wrote: > > > > > It seems that, when masquerading, conntrack silently drops idle > > > > > connection after nf_conntrack_tcp_timeout_established seconds. This's > > > > > pretty terrible, as application inside the network, if it never sends > > > > > anything, will never know that connection was dropped. > > > > > > > > If this is a problem for you, then increase nf_conntrack_tcp_timeout_established > > > > to an insanely high value. You do realize, of course, that the conntrack > > > > table has a finite number of entries. > > > > > > > > > RFC 5382 gives us a solution to this: > > > > > > A NAT can check if an endpoint for a session has crashed by sending a > > > > > > TCP keep-alive packet and receiving a TCP RST packet in response. > > > > > > > > > > However, it I couldn't find such feature in netfilter. It would be > > > > > pretty nice to have. > > > > > > > > Keepalives should be done in the application, not in the firewall. > > > > > > Actually I think its a pretty nice idea to reduce breakage introduced > > > by NATs. There a millions of embedded devices that use very small timeout > > > values to reduce memory usage, at the cost of frequently breaking idle > > > connections. > > > > The downside seems to be that we'd need to keep track of timestamp values > > to send valid keepalives, which also costs extra memory. I don't think that > > cost is justifiable for NAT keepalives alone. > > I think a single flag could be sufficient: if the timer in conntrack goes > off and the entry is in the ESTABLISHED state and this flag is not set, > then send a TCP keepalive packet and start the timer with a short timeout. > If we receive the reply packet, then the long ESTABLISHED timeout value > can be restored and the flag cleared. Sure, I think we wouldn't even need that flag, we can just send the keepalive and set a short timeout. If a RST is received, the connection is killed anyway, otherwise it will be refreshed with the ESTABLISHED timeout. But we do need a timestamp value to pass PAWS. -- 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
