11.12.2017 2:54, Michael Grimm wrote: > I did already lower MTU: If I do configure vtnet0 to a MTU of 1490 at boot > time I do not not notice a performance loss compared to the default 1500 > setting. > >>> *BUT* if I do a "ifconfig vtnet0 mtu 1450 up ; ifconfig vtnet0 mtu 1500 up" >>> I do observe: >>> >>> #) scp NEW to OLD via IPsec tunnel: 17.1 MB/s ! >>> #) scp OLD to NEW via IPsec tunnel: 16.9 MB/s > > > *BUT* if I do boot with the default 1500 setting, > changing the MTU to e.g. 1450 and *immediately* back to 1500 manually, > I do not encounter any performance loss at all. Why? > Even when booting 1490 and immediately setting the MTU manually to 1500 I do > not see any performance loss. Strange.
Interface MTU is used to assing 'mtu' attribute to corresponding route in the system routing table. Lowering interface MTU lowers route mtu, but raising interface MTU does *not* raises route mtu, use "route -n get" command to check it out. So, you still use low mtu really. >> To verify if it's your case, you should run two tcpdump commands, >> one at sending side and another at receiving size >> and compare outputs to see if *every* outgoing packet reaches its >> destination or not. > > Hmm, how would one check that? The output is to fast for me ;-) Seriously, > how should one check this? With your eyes :-) Use tcpdump -c flag to limit number of lines, redirect output to a file and carefully compare some packets using their ID that tcpshow shows. _______________________________________________ freebsd-net@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
