Openvpn disruption when active VM with bridged network

[Giovanni Toraldo (gionn)]

I have a Mac OSX 10.6.2 as host, and I use a Debian Lenny as guest for development purposes with ethernet bridging.

I often use vpn connections on Mac host, with tunnelblick (​http://code.google.com/p/tunnelblick/). For the first time today, I noticed some strange behavior with a new vpn configuration, resulting in very poor nfs performances, going stall completely after few minutes.

Another (nice) problem I get, is with ssh through the same vpn:

scorp@antani-mac:~$ ssh -l libersoft 192.168.1.1
Last login: Wed Feb 24 18:02:36 2010 from vpn.libersoft.bncf.lan
libersoft@nfs-server:~$ exit
scorp@antani-mac:~$ ssh -l 123456789 192.168.1.1
123456789@192.168.1.1's password:

scorp@antani-mac:~$ ssh -l root 192.168.1.1
Read from socket failed: Operation timed out
scorp@antani-mac:~$ ssh -l 1234567 192.168.1.1
Read from socket failed: Operation timed out

With an username > 8 chars, ssh connects almost instantly, with an username <= 8 chars, the session seems to start, but some answer from remote server get lost or my packages never get transmitted (note the retransmissions on the tcpdump for login <= 8 chars).

My dmesg shows (a lot of):

in_delayed_cksum_offset: ip_len 49408 (193) doesn't match actual length 207
in_delayed_cksum_offset: ip_len 49408 (193) doesn't match actual length 207
in_delayed_cksum_offset: ip_len 49408 (193) doesn't match actual length 207

If I shutdown (or even pause) every guest VM using bridged networking, the problem disappears.

The only reason I can find in this particular vpn config, is that it use udp packets (In the past I always used tcp-based ones).

[Giovanni Toraldo (gionn)]

VBox log

[Giovanni Toraldo (gionn)]

Tcpdump of the ssh session that works (username > 8)

[Giovanni Toraldo (gionn)]

Tcpdump of the ssh session that *doesn't* works (username <= 8)