More then 32 bfp devices on Freebsd 5.4-RELEASE-p7

Peter Wood peter at
Mon Oct 17 06:11:23 PDT 2005

Good Afternoon,

I'm now working at a large UK university in their network support 
department, as such one of my duties is to monitor the residences 
network. To this end I have a cloned nic for every vlan that we have on 
resnet. It roughly comes to over 50 vlans, and FreeBSD its self copes 
very nicely.

However I've run into a small problem when using nmap (and a tiny one in 
Ethereal). Unless you specify the source address and source interface 
for scans nmap will open every network device with bpf. The problem 
comes when it hits the 33rd interface to open, nmap exits.

[eclair:~]# nmap -P0 -p 1-65535 -sS
Starting nmap 3.93 ( ) at 2005-10-17 14:03 BST
getinterfaces: Failed to open ethernet interface (resnet737)

If I truss I get the following:

open("/dev/bpf29",0x1,01002230274)               ERR#16 'Device busy'
open("/dev/bpf30",0x1,01002230274)               ERR#16 'Device busy'
open("/dev/bpf31",0x1,01002230274)               ERR#16 'Device busy'
write(2,0xbfbfab40,60)                               = 60 (0x3c)
getinterfaces: Failed to open ethernet interface (resnet737)

So the question is, how can I allow more then 32 bpf devices, in the old 
4.X series I'd have just tagged a number on the end of the kernel line.

Any suggestions apreciated,


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