VirtualBox

Opened 11 years ago

Closed 9 years ago

#11871 closed defect (fixed)

NAT drops packets bigger than 388 byte towards guest

Reported by: Lukas Tribus Owned by:
Component: network/NAT Version: VirtualBox 4.2.12
Keywords: mtu Cc:
Guest type: all Host type: all

Description

NAT mode does not work for me, because all packets bigger than 388 byte (IP packet length; 368 byte IP payload or 360 byte ICMP payload) are dropped.

The test is as simple as:

ping google.com -s 360
ping google.com -s 361

or on Windows guests:

ping google.com -l 360
ping google.com -l 361

The former (360 byte ICMP payload) works, while the latter (361 byte ICMP payload) doesn't.

I can reliably reproduce this with both Linux and Windows guests (32 and 64bit), on different hardware. The host always runs Windows Vista or Windows 7, both 64 bit. I did not test different host OS'.

This is with VirtualBox-4.2.12, but I can also reproduce this with the old VirtualBox-3.2.16.

The traffic of the testcase has been captured:

nictrace.cap
via the nictrace feature; it is clear that the answer packets do not reach the guests
host-dump.cap
via Wireshark on the host; all answer packets are seen (frame >= 25)

I have no clue why others don't see this behavior; on all my VirtualBox installations I see exactly this issue, and they are different installations on different hardware with different software.

Bridging mode works perfectly fine on those installations.

Attachments (4)

VBox.log (72.1 KB ) - added by Lukas Tribus 11 years ago.
nictrace.cap (14.4 KB ) - added by Lukas Tribus 11 years ago.
host-dump.cap (19.0 KB ) - added by Lukas Tribus 11 years ago.
vbox-doc-win-nat-icmp-clarification.diff (841 bytes ) - added by Lukas Tribus 11 years ago.
doc clarification patch

Download all attachments as: .zip

Change History (12)

by Lukas Tribus, 11 years ago

Attachment: VBox.log added

by Lukas Tribus, 11 years ago

Attachment: nictrace.cap added

by Lukas Tribus, 11 years ago

Attachment: host-dump.cap added

comment:1 by vasily Levchenko, 11 years ago

What was initial problem (before you had gone down to ping diagnostic)? (please note: for Windows host ICMP isn't implemented in socket API, instead ICMP API used, which has own bottlenecks and couldn't be used as diagnostic tool).

comment:2 by Lukas Tribus, 11 years ago

The initial problem was that my DNS servers are within the default NAT range 10.0.2.0/24, so the guest could never contact them. I erroneously concluded that DNS wasn't working because of MTU problems and I fixed it only now, by changing the NAT range in VirtualBox to something which doesn't conflict with my upstream DNS servers.

So if I understand this correctly, this is a known limitation impacting ICMP traffic only; when the host is Windows and NAT is used? Perhaps this should be made more clear in the manual?

Chapter 6, NAT limitations:

While ICMP support has been improved with VirtualBox 2.1 (ping should now work), some other tools may not work reliably.


I suppose we should add your statement from above:

Please note: for Windows hosts ICMP isn't implemented in socket API, instead ICMP API used, which has own bottlenecks and couldn't be used as diagnostic tool. This affects all guests.

Last edited 11 years ago by Lukas Tribus (previous) (diff)

by Lukas Tribus, 11 years ago

doc clarification patch

comment:3 by Lukas Tribus, 11 years ago

Kindly requesting review of the attached doc patch. Thank you.

comment:4 by Frank Mehnert, 9 years ago

Actually we changed the implementation. Could you check if this build fixes the problem for you?

in reply to:  4 comment:5 by Lukas Tribus, 9 years ago

I only check it now (no notifications possible here?) and the link doesn't work.

Should I wait for the next Virtualbox 4.3 release?

Version 0, edited 9 years ago by Lukas Tribus (next)

comment:6 by Frank Mehnert, 9 years ago

Re notifications: Check your email address in the preferences. Here is a new build.

comment:7 by Lukas Tribus, 9 years ago

I can confirm that this issue is no longer occurring in the newer testbuilds, Thank you!

comment:8 by Frank Mehnert, 9 years ago

Resolution: fixed
Status: newclosed

Fix is part of VBox 4.3.22.

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