Packet loss

[Albert Nguyen]

I'm using VBox 4.2.16. Host: Windows 7. Guest: Arch Linux. VM network adapter's attached to NAT. SSH connection from the Internet to my guest is rather slow. I found out on the guest:

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$ ping 23.50.16.170 -f -i 0.2
PING 23.50.16.170 (23.50.16.170) 56(84) bytes of data.
..........^C
--- 23.50.16.170 ping statistics ---
106 packets transmitted, 96 received, 9% packet loss, time 21311ms
rtt min/avg/max/mdev = 42.060/47.428/92.008/9.512 ms, ipg/ewma 202.967/46.545 ms

Packet capture on the host showed that 23.50.16.170 (Cisco) sent ICMP responses but the host did not deliver all of them to the guest (see attachment). The host & the guest were not overloaded, for example the guest:

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%Cpu(s):  0.1 us,  0.0 sy,  0.0 ni, 99.9 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:    248128 total,    71260 used,   176868 free,     7984 buffers

I could reproduce this problem on another machine running VBox 4.1.22, Host: Windows 2003, Guest: Ubuntu, with another ICMP destination.

Please help.

Thanks.

[mpack]

ICMP (ping) is not reliable over NAT.

From the current (v4.2.16) user manual section 6.3.3 :-

6.3.3 NAT limitations
There are four limitations of NAT mode which users should be aware of:
ICMP protocol limitations: Some frequently used network debugging tools (e.g. ping or tracerouting) rely on the ICMP protocol for sending/receiving messages. While ICMP support has been improved with VirtualBox 2.1 (ping should now work), some other tools may not work reliably.

Another thing to note is, if you are using NAT then the guest doesn't have an independant network connection. In effect VirtualBox is just another application using the hosts networking stack. So, the guest shouldn't be relevant to host network performance problems.