Suspected network performance issue on VirtualBox Ubuntu guest on Win7 host

Question

I have narrowed down a performance problem in my Ubuntu guest on a Win7 VirtualBox host to the network, after comparing and equalising everything else to do with my slow-running Java app with a colleague who runs the same app under Win7.

I set up Ubuntu 12.04 in VirtualBox on the Win7 machine I was allocated on my new project. I am running Java, Eclipse, Tomcat to develop a large data-intensive application and this app literally runs at half the speed of my colleague's identical machine.

Is there a ping test I can do or some other network diagnostic test to flag up any problems? I will accept any answer that will just get me moving forward - I don't expect anyone to come up with a blinding solution for the issue.

To give some background, the network performance is confusing.

Running a network speed test to my colleague's machine with iperf shows speeds of 6 Mb/s from my Ubuntu guest, and 90 Mb/s from the win7 host.

Large downloads, e.g. the Java SDK, come down at about 1.2 MB/s on both the guest and the host.

Pings are sub-1ms on the host, but 1.5ms on the guest.

I also did a broadband speed test, and got 10Mb/s download speed on both, but the host has an upload speed of 10Mb/s but the guest only uploads at 3Mb/s.

I've been trying to diagnose any MTU problems with ping -M do to identify any kind of packet fragmentation problem but it's progressing very slow because I don't have much experience in this area.

From what I read on other people's networking issues with VB and Linux guests on Win7 hosts, I should be able to get the speed on the guest up to the same level as the host.

I installed a fresh VM with Ubuntu again to see if I'd foobar'd it somehow, but I'm getting the same readings with iperf on the virgin installation.

My setup is:

Adapter 1: Intel PRO/1000 MT Desktop (NAT)

Adapter 2: ditto (host-only adapter)

eth0      Link encap:Ethernet  HWaddr 08:00:27:0b:76:bf  
          inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe0b:76bf/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:86236 errors:0 dropped:0 overruns:0 frame:0
          TX packets:49369 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:69163946 (69.1 MB)  TX bytes:3530535 (3.5 MB)

eth2      Link encap:Ethernet  HWaddr 08:00:27:a3:26:b8  
          inet addr:192.168.56.101  Bcast:192.168.56.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fea3:26b8/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:59 errors:0 dropped:0 overruns:0 frame:0
          TX packets:57 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:9148 (9.1 KB)  TX bytes:7648 (7.6 KB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:701 errors:0 dropped:0 overruns:0 frame:0
          TX packets:701 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:66321 (66.3 KB)  TX bytes:66321 (66.3 KB)