Bad UDP checksums from host

[RichN]

Hello,

I'm running VirtualBox 4.1.6 on an iMac (Snow Leopard). My guest OS is NetBSD 5.1/amd64 and it is using ethernet in a bridged configuration.

Both systems communicate with other systems using a UDP protocol. We recently noticed a problem where it appeared the communications was failing. tcpdump showed the packet arrived at the destination, but it contained a bad checksum and was being dropped. We varied the size of the packet and found there was a range of sizes in which the OSX system would consistently generate a bad checksum. If we completely shut down and quit VirtualBox, the Mac is able to communicate successfully. We find the checksum errors happen anytime VirtualBox is running -- even before NetBSD (the guest OS) has started to boot. We've tried every VirtualBox network interface; we're currently using the Intel interface. None fix the problem.

This is a packet that always generates a bad checksum (the packet starts at offset 0x001c):

0x0000:  4500 00c6 7ebd 0000 4011 fe12 **** ****  E...~...@...****
0x0010:  **** **** 1a91 1a91 00b2 fe1a 0002 0000  ****............
0x0020:  490e 0e0d 4d67 4818 005b 4c73 00aa 4453  I...MgH..[Ls..DS
0x0030:  0244 0351 e314 21e3 1232 c641 0251 2e12  .D.Q..!..2.A.Q..
0x0040:  5154 410e 4708 423a 5943 4c43 4145 5608  QTA.G.B:YCLCAEV.
0x0050:  4f3a 4550 4d52 4144 4906 423a 4145 414d  O:EPMRADI.B:AEAM
0x0060:  5206 423a 4145 414d 5607 4d3a 4d49 444f  R.B:AEAMV.M:MIDO
0x0070:  0741 3a56 5252 4f4d 4144 4708 533a 5443  .A:VRROMADG.S:TC
0x0080:  4d49 4145 4d08 4f3a 5455 4d54 4150 4c07  MIAEM.O:TUMTAPL.
0x0090:  493a 4f54 3152 0741 3a4c 3744 4f54 4152  I:OT1R.A:L7DOTAR
0x00a0:  4206 433a 4748 4132 4508 543a 524f 3031  B.C:GHA2E.T:RO01
0x00b0:  4131 4508 543a 5447 5750 4152 4508 4d3a  A1E.T:TGWPARE.M:
0x00c0:  5242 5441 0045                           RBTA.E

The interesting thing is that the guest OS always seems to generate a correct checksum (we haven't found any packets which fail.) Only the host is affected and only when VirtualBox is running.

If anyone has anything else we could try, or any solutions, we'd appreciate to hear from you! Thanks!

[Technologov]

It could be hardware TCP/UDP checksum offload engine. Some drivers do this.

[RichN]

It could be hardware TCP/UDP checksum offload engine. Some drivers do this.

But it seems to be VirtualBox-related since the problem occurs only when VirtualBox is running. Maybe the VirtualBox drivers are setting up the hardware to do the checksumming, but it's impacting the Host system, so it's seems to be a bug.