[Simh] Problem with Ethernet on Vax

[Dan Williams]

I know this is probably a libpcap problem but I though I'd ask here first
I have just compiled simh on my Mac Laptop (Having used it for a
number of years on Linux and Windows).
I can only connect the first ethernet device (en0) to the emulator. If
I try to use any other network devices I get a "File open error". When
I run "tcpdump -D" I get the following :

1.en0
2.fw0
3.en1
4.wlt1
5.en2
6.en3
7.lo0

Does anyone know of any reason why the any of the other devices cannot be used ?

Thanks
Dan