Bridge Networking MTU issue

[dinuzabrauteanu]

Hello,

I am using Mac OS X Lion release 10.7.4 using VirtualBox 4.2.0 r80737 with a Windows XP Pro SP 3 guest and the following network configuration

Bridged
en0: Ethernet (not wireless!)

PCnet-Fast III (Am79C973)
OR
the Intel Pro 1000 T Server

the LARGEST MTU usable is 1400. This is likely related to a regression on this existing bug:

Ticket: 3783


Where did the other 1000 bytes of the possible MTU go? The hardware is at 1500 on the Mac, as confirmed by a MacOS "ping -D -s 1472 <ip address" being successful.

I currently have my MTU set at 1372 and things seem fine, but it is very concerning that Bridged mode in VirtualBox on MacOS behaves differently than on Solaris.

Is this a known bug ? If so, is there anything we can do about it ? I can reproduce this bug on any Mac OS X Lion release 10.7.4 with WinXP as VM. This is not a network issue as I have tried from multiple Internet providers, routers, firewalls and with multiple Mac hardware on same software release.

I would like to solve this issue as soon as possible.

Thank you !
Dinu