freebsd stable - Aug 2005 - 5.4-STABLE freezing without hints in verbose mode

Using:
5.4-STABLE FreeBSD 5.4-STABLE #1: Tue Aug 16 16:45:31 CST 2005
with this kernel config:
include SMP
ident   IDS
options NETGRAPH

having 3 network interfaces:
One with ip address(fxp0), the other two (xl0 and xl1) are just to sniff traffic
on different
networks, at the begining unplugged, sending traffic to one virtual
NIC using netgraph like this:

# ngctl mkpeer . eiface lower ether     [ngeth0]
# ngctl mkpeer . ether lower            [xl0 xl1 fxp0 ether0]
# ngctl mkpeer ngeth0: hub ether link0  [hub0]
# ifconfig [xl0,xl1,ngeth0] up
# ngctl connect xl0: hub0: lower link1
# ngctl connect xl1: hub0: lower link2
# ifconfig [xl0,xl1] promisc

ngctl list shows:
There are 7 total nodes:
  Name: ngctl688        Type: socket          ID: 00000045   Num hooks: 0
  Name: hub0            Type: hub             ID: 0000001e   Num hooks: 3
  Name: ether0          Type: ether           ID: 0000000f   Num hooks: 0
  Name: fxp0            Type: ether           ID: 0000000e   Num hooks: 0
  Name: xl1             Type: ether           ID: 0000000d   Num hooks: 1
  Name: xl0             Type: ether           ID: 0000000c   Num hooks: 1
  Name: ngeth0          Type: eiface          ID: 00000006   Num hooks: 1


By now everything is working fine, but if I plug xl0 and xl1 the server will 
freeze after some time, not even the BloqNum key will respond, and I can't
take anything out of /var/log,
I didn't include dmesg because it seems like a kernel loop, it is running in
verbose mode(option 5 while booting),
but it is not helping.

Is there anything that I can do to see what is going on ?