Weird source MAC address on a virtual Ethernet interface
Weird source MAC address on a virtual Ethernet interface
- Subject: Weird source MAC address on a virtual Ethernet interface
- From: "Joshua Zhao" <email@hidden>
- Date: Mon, 7 Oct 2002 22:57:43 -0700
- Thread-topic: Weird source MAC address on a virtual Ethernet interface
I ran into a puzzling problem with an NKE that presents itself as a
virtual Ethernet device. I wish that some Mac OS kernel guru out there
would be able to shed some light on it.
My NKE code is based on the Mac OS VLAN NKE code from the Darwin web
site and the tunnel KEXT code (based on FreeBSD's tun driver). What the
driver does is to function as an Ethernet device, except that frames
sent through it are actually looped back to an application program where
they are encapsulated before being transmitted through a real Ethernet
interface, much like the ethertap driver does under Linux. I have set
the source MAC address of the virtual Ethernet interface to be the same
as its underlying real Ethernet device, and "ifconfig" seems to indicate
that the MAC address is set properly. However, the problem is that the
frames, such as ARP requests sent through this virtual Ethernet
interface, have the source MAC address being something different from
what it was set to. To be more specific, the source MAC address in the
Ethernet header of the virtual Ethernet interface resembles the MAC
address of the real Ethernet interface, i.e. 2 higher in the last digit.
Changing the unit number of the virtual Ethernet interface doesn't make
any difference at least on my ibook. I'm quite puzzled by this problem,
and I'm hoping someone more familiar with Mac OS kernel internals could
offer some advices on things for me to check.
Any suggestion would be greatly appreciated!
Joshua
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