ng_wlan FreeBSD kernel module

(c) 2006-2011 the Boeing Company
author: Jeff Ahrenholz <jeffrey.m.ahrenholz@boeing.com>


  The ng_wlan modules implements a netgraph node that models wireless 
LAN connectivity. ng_wlan extends the ng_hub node, only instead of sending 
packets to each connected peer, maintains a hash table of node connectivity,
and sends packets between two nodes only when they are linked. By default all
nodes are unlinked. Nodes can be linked and unlinked using "link" and
"unlink" messages:
    ngctl msg e0_n2: link { node1=0x23 node2=0x0c }
    
The node IDs of the two nodes are the parameters, as depicted above.

  Link effects between can also be specified for each node pair. If two nodes
are linked and parameters are specified, an mbuf tag will be added to each data
packet mbuf that specifies the effects. For FreeBSD 4.11, the metadata parameter
is used instead of mbuf tags. Delay (microseconds), bandwidth 
(bits per second), PER (% packet errors), duplicates (%), jitter 
(microseconds), and burst (% burst errors) are supported. This tag is then
removed by the ng_pipe node and the appropriate effects are applied. Link
effects are specified with "set" and "unset" messages:
    ngctl msg e0_n2: set { node1=0x23 node2=0x0c delay=50000 bandwidth=54000000 per=0 duplicate=0 jitter=5000 burst=30 }
    ngctl msg e0_n2: unset { node1=0x23 node2=0x0c }

Note that a special ng_pipe module is needed (the default one does not support
the mbuf tags and some effects.)

A separate error rate and burst rate affecting all multicast packets may be
defined. Use the "mer" message:
    ngctl msg e0_n2: mer { mer=20 mburst=35 }
The above example sets the multicast error rate to drop 20% of all multicast
packets, with 35% burst errors.

When MULTICAST_LOOKUPS is defined, a second lookup table is defined for each
WLAN where multicast group, source, and node pair tuples can be linked or 
unlinked. This causes different forwarding behavior for multicast packets,
where non-local groups are only forwarded if the node pair has been linked
together for that group (and the normal node pair has been linked).
Usage:
    ngctl msg e0_n2: mcastset { node1=0x23 node2=0x0c group=0xEF020364 source=0x0a000002 }
    ngctl msg e0_n2: mcastset { node1=0x23 node2=0x0c group=0xEF020364 source=0}
    ngctl msg e0_n2: mcastunset { node1=0x23 node2=0x0c group=0xEF020364 source=0 }
Once the first mcastset/mcastunset message is received, that ng_wlan will drop
all non-local multicast packets that do not have a matching source, group,
node pair entry. The source address of zero matches any IP source.