On Fri, 08 May 2015 21:24:13 +0200 David du Colombier <0in...@gmail.com> wrote: > On the loopback medium, I suppose this is the opposite issue. > Since the TCP stack didn't fix the MSS in the incoming > connection, the programs sent multiple small 1500 bytes > IP packets instead of large 16384 IP packets, but I don't > know why it leads to such a slowdown.
Looking at the first few bytes in each dir of the initial TCP handshake (with tcpdump) I see: 0x0000: 4500 0030 24da 0000 <= from plan9 to freebsd 0x0000: 4500 0030 d249 4000 <= from freebsd to plan9 Looks like FreeBSD always sets the DF (don't fragment) bit (0x40 in byte 6), while plan9 doesn't (byte 6 is 0x00). May be plan9 should set the DF (don't fragment) bit in the IP header and try to do path MTU discovery? Either by default or under some ctl option.