Bandwith from Host to Guest limited by the real ethernet mounted on host.

[Giovanni Toraldo (gionn)]

virtualbox-ose 3.0.6-dfsg-1~bpo50+1 (debian lenny-backports)

I caught a behavior that I wasn't expecting

I have a Debian Lenny amd64 host with a gigabit network card but, unfortunately, attached to a 10/100 switch: 02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)

I setup a Debian Lenny i386 guest with a gigabit network card: 00:11.0 Ethernet controller: Intel Corporation 82545EM Gigabit Ethernet Controller (Copper) (rev 02)

I was hoping that between host and guest, i will get full gigabit speed, but instead, I've host outgoing bandwidth limited by *real* speed.

Here the output of two iperf sessions:

Host -> Guest [ 4] local 192.168.1.2 port 5001 connected with 192.168.1.10 port 54853 [ ID] Interval Transfer Bandwidth [ 4] 0.0-10.1 sec 114 MBytes 94.1 Mbits/sec [ 5] local 192.168.1.2 port 5001 connected with 192.168.1.10 port 54854 [ 5] 0.0-10.2 sec 114 MBytes 94.1 Mbits/sec [ 4] local 192.168.1.2 port 5001 connected with 192.168.1.10 port 54856 [ 4] 0.0-10.2 sec 114 MBytes 94.1 Mbits/sec

Guest -> Host [ 4] local 192.168.1.10 port 5001 connected with 192.168.1.2 port 46946 [ ID] Interval Transfer Bandwidth [ 4] 0.0-10.0 sec 412 MBytes 345 Mbits/sec [ 5] local 192.168.1.10 port 5001 connected with 192.168.1.2 port 46947 [ 5] 0.0-10.0 sec 402 MBytes 337 Mbits/sec [ 4] local 192.168.1.10 port 5001 connected with 192.168.1.2 port 46948 [ 4] 0.0-10.0 sec 382 MBytes 320 Mbits/sec

So, it's the outgoing data from host to guest passed to the wire before getting into the guest? Is this an expected behaviour? Should I use a host-only network for having full transfer speeds?