[VMware ESX 5.5 ]ESX Jumbo frames truncating 4 byte CRC for packet length between 2049 to 2052

[HAkshay]

Hi ,

I am using ESX 5.5 where at host level I have set MTU of interface 9000. Guest is freebsd. Using e1000 nics. At guest level, I have enabled jumbo setting and set MTU of interface 9000.

I am splitting Jumbo frames at boundary of 2048 when they arrive at guest VM.

So when I send a packet of length 2050.ideally I should get two packet, one of length 2046 and second one of 4 byte (CRC will come at next packet.) .

But at guest level I am getting only one packet of length 2046 with CRC deducted.

But if I send a packet of length 2053, I am getting two packets properly without CRC deduction,(packet one 2049 byte and packet two 4 byte)

This is happening for all packet with length on boundary 2048. For example packet with length 2049 to 2052, 4097 to 4100 etc.

Can someone help me in this issue? Where am I going wrong or is it problem with e1000 nics only?

Thanks

Akshay

[MKguy]

Unfortunately I can't really help you but this seems awfully similar to this issue:

TCP segments truncated by 4 bytes in Inter-vm communication on esxi 5.1

I've been using Jumbo Frames for vMotion and iSCSI vmkernel adapters and never noticed issues until now.

I would recommend upgrading to the latest 5.5 patches and the VM hardware version.

The e1000 vNIC caused lots of issues lately (mainly with PSODs), is there any reason why you can't switch to vmxnet3? Not sure which FreeBSD version you're using or if the vmxnet3 kernel module is already part of the default FreeBSD kernel, but vmxnet3 is supported on FreeBSD 9.x and 10.x:

VMware Compatibility Guide: Guest/Host Search

VMware Compatibility Guide: Guest/Host Search

In the worst case you'll have to install the VMware Tools or manually enable/compile the FreeBSD-provided driver:

http://www.freebsd.org/cgi/man.cgi?query=vmx&sektion=4

Apart from that you could test the e1000E vNIC by editing the .vmx file since it may not show up in the GUI:

Choosing a network adapter for your virtual machine