Creating span port using netgraph

Frank frank at
Sat Jan 28 11:52:12 PST 2006


I'm trying to setup a "span" Interface for using with snort. Basically, 
the span interface should receive a copy of all IP packets seen on my 
real network interfaces, with the purpose that snort can snoop this 

After reading the manuals, and searching the Internet I came up with the 
following script:


# load ng_ether to get ethernet interfaces
if ! kldstat -v | grep ng_ether > /dev/null 2>&1; then
         kldload ng_ether

# create ngeth0 and bind xl0, xl1, xl2 and xl3 to it
ngctl mkpeer . eiface hook ether
ngctl mkpeer ngeth0: one2many lower one
ngctl connect xl0: ngeth0:lower lower many0
ngctl connect xl1: ngeth0:lower lower many1
ngctl connect xl2: ngeth0:lower lower many2
ngctl connect xl3: ngeth0:lower lower many3

# bring up ngeth0 for sniffing duties
ifconfig ngeth0 monitor up

After I run this script, all network connections freeze and I lost all 
IP connectvity. If I tcpdup on any inteface (xl? or ngeth0) no traffic 
is visible.

Maybe I'm overlooking the obvious, but I do not understand why it does 
not work....

Any help is appreciated! I'm using FreeBSD 6-STABLE.



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