[apologies for top-posting] What is the result of
> sysctl net.enc ? This might be a clue about the packets, which you could be seeing twice. On Sat, Jan 18, 2020 at 3:17 AM Eugene Grosbein <eu...@grosbein.net> wrote: > 18.01.2020 17:55, Victor Sudakov wrote: > > >>>>> Back to the point. I've figured out that both encrypted (in transport > >>>>> mode) and unencrypted TCP segments have the same MSS=1460. Then I'm > >>>>> completely at a loss how the encrypted packets avoid being > fragmented. > >>>>> TCP has no way to know in advance that encryption overhead will be > >>>>> added. > > > > Here: http://admin.sibptus.ru/~vas/ftp-pcap.tar.gz you can find two > > identical FTP sessions, the only difference being ipsec=off during one > > session and ipsec=on during the other one. > > > > As I said, in both the sessions MSS=1460 which is already odd, and I > > can't explain to myself why file transfer still works without MSS > > ajustment. > > > > Moreover, something fishy is happening in the encrypted session: there > > are many TCP retransmissions (I was capturing on the FTP server's side, > > so there are many segments with the same sequence number). How would you > > explain this? There are almost no retransmissions in the unencrypted > session. > > > > All this is happening in a lab environment (one bhyve VM is an FTP > > server and the other downloads a file from the first), both VMs are on > > the same bridge interface. There are almost 19,000 packets in the > > encrypted file vs 12,000 in the plain file, I think because of those > > excessive retransmissions. > > > > Could the retransmissions be some artifact of the enc(4) interface I was > > capturing the encrypted session on? > > I doubt it. And I can't explain this, but maybe it's work of PMTUD > Blackhole detection? > Look at sysctl net.inet.tcp | fgrep blackhole_ > > _______________________________________________ > 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" > -- "Well," Brahmā said, "even after ten thousand explanations, a fool is no wiser, but an intelligent person requires only two thousand five hundred." - The Mahābhārata _______________________________________________ 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"