Liked the simplification of MSS bytes = MTU bytes + IP header bytes. With TSO turned on in hardware (find out by ethtool -k eth0) then latency skyrocketed.
On 12/18/10, Guus Sliepen <[email protected]> wrote: > On Fri, Dec 17, 2010 at 01:17:22AM -0600, Rob Townley wrote: > >> An OpenVPN user on the vyatta.org forums had the problems with >> excessively slow connections. >> >> He found that either lowering the MTU to about one-third helped: >> router:~# ifconfig vtun0 mtu 516 > > Ugh. I cannot recommend setting the MTU so low. > >> But also found turning OFF TCP Segmentation Offload (TSO) on the >> server speeded things up just as well. As i understand it, the word >> segment in this context refers to Maximum Segment Size which is broken >> down to ethernet MTU frame size (usually 1500bytes). > > Almost correct. MSS is the same as MTU, minus the IP header. TSO means that > if > you send lots of data through a TCP connection at once, the hardware will > take > care of splitting the data up in MSS sized chuncks, and will generate a > header > for all of them. > > The problem with these hardware features is that the NIC hardware is often > slower than your CPU. > >> So if you have TSO enabled on your NICs but the tun device doesn't support >> TSO, couldn't that create a problem? > > That should not be a problem. Segmentation is only done once, on the first > outgoing interface. If the OpenVPN connection was faster with TSO turned > off, > then OpenVPN was tunneling over TCP. That is slow in itself. > > -- > Met vriendelijke groet / with kind regards, > Guus Sliepen <[email protected]> > _______________________________________________ tinc mailing list [email protected] http://www.tinc-vpn.org/cgi-bin/mailman/listinfo/tinc
