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NG_BRIDGE(4)	       FreeBSD Kernel Interfaces Manual		  NG_BRIDGE(4)

NAME
     ng_bridge -- Ethernet bridging netgraph node type

SYNOPSIS
     #include <sys/types.h>
     #include <netgraph/ng_bridge.h>

DESCRIPTION
     The bridge	node type performs Ethernet bridging over one or more links.
     Each link (represented by a connected hook) is used to transmit and
     receive raw Ethernet frames.  As packets are received, the	node learns
     which link	each host resides on.  Packets unicast to a known host are
     directed out the appropriate link only, and other links are spared	the
     traffic.  This behavior is	in contrast to a hub, which always forwards
     every received packet to every other link.

LOOP DETECTION
     The bridge	node incorporates a simple loop	detection algorithm.  A	loop
     is	when two ports are connected to	the same physical medium.  Loops are
     important to avoid	because	of packet storms, which	severely degrade per-
     formance.	A packet storm results when the	same packet is sent and
     received over and over again.  If a host is detected on link A, and is
     then detected on link B within a certain time period after	first being
     detected on link A, then link B is	considered to be a looped back link.
     The time period is	called the minimum stable time.

     A looped back link	will be	temporarily muted, i.e., all traffic received
     on	that link is ignored.

IPFW PROCESSING
     Processing	of IP packets via the ipfirewall(4) mechanism on a per-link
     basis is not yet implemented.

HOOKS
     This node type supports up	to NG_BRIDGE_MAX_LINKS hooks.  Each connected
     hook represents a bridged link.  The hooks	are named link0, link1,	etc.
     Typically these hooks are connected to the	lower hooks of one or more
     ng_ether(4) nodes.	 To connect the	host machine to	a bridged network,
     simply connect the	upper hook of an ng_ether(4) node to the bridge	node.

CONTROL	MESSAGES
     This node type supports the generic control messages, plus	the following:

     NGM_BRIDGE_SET_CONFIG
	  Set the node configuration.  This command takes a struct
	  ng_bridge_config as an argument:

	  /* Node configuration	structure */
	  struct ng_bridge_config {
	    u_char	ipfw[NG_BRIDGE_MAX_LINKS]; /* enable ipfw */
	    u_char	debugLevel;	      /* debug level */
	    u_int32_t	loopTimeout;	      /* link loopback mute time */
	    u_int32_t	maxStaleness;	      /* max host age before nuking */
	    u_int32_t	minStableAge;	      /* min time for a	stable host */
	  };

	  The ipfw array enables ipfirewall(4) processing of IP	packets
	  received on the corresponding	links.	The debugLevel field sets the
	  debug	level on the node.  At level of	2 or greater, detected loops
	  are logged.  The default level is 1.

	  The loopTimeout determines how long (in seconds) a looped link is
	  muted.  The default is 60 seconds.  The maxStaleness parameter
	  determines how long a	period of inactivity before a host's entry is
	  forgotten.  The default is 15	minutes.  The minStableAge determines
	  how quickly a	host must jump from one	link to	another	before we
	  declare a loopback condition.	 The default is	one second.

     NGM_BRIDGE_GET_CONFIG
	  Returns the current configuration as a struct	ng_bridge_config.

     NGM_BRIDGE_RESET
	  Causes the node to forget all	hosts and unmute all links.  The node
	  configuration	is not changed.

     NGM_BRIDGE_GET_STATS
	  This command takes a four byte link number as	an argument and
	  returns a struct ng_bridge_link_stats	containing statistics for the
	  corresponding	link, which must be currently connected:

	  /* Statistics	structure (one for each	link) */
	  struct ng_bridge_link_stats {
	    u_int64_t	recvOctets;	/* total octets	rec'd on link */
	    u_int64_t	recvPackets;	/* total pkts rec'd on link */
	    u_int64_t	recvMulticasts;	/* multicast pkts rec'd	on link	*/
	    u_int64_t	recvBroadcasts;	/* broadcast pkts rec'd	on link	*/
	    u_int64_t	recvUnknown;	/* pkts	rec'd with unknown dest	addr */
	    u_int64_t	recvRunts;	/* pkts	rec'd less than	14 bytes */
	    u_int64_t	recvInvalid;	/* pkts	rec'd with bogus source	addr */
	    u_int64_t	xmitOctets;	/* total octets	xmit'd on link */
	    u_int64_t	xmitPackets;	/* total pkts xmit'd on	link */
	    u_int64_t	xmitMulticasts;	/* multicast pkts xmit'd on link */
	    u_int64_t	xmitBroadcasts;	/* broadcast pkts xmit'd on link */
	    u_int64_t	loopDrops;	/* pkts	dropped	due to loopback	*/
	    u_int64_t	loopDetects;	/* number of loop detections */
	    u_int64_t	memoryFailures;	/* times couldn't get mem or mbuf */
	  };

     NGM_BRIDGE_CLR_STATS
	  This command takes a four byte link number as	an argument and	clears
	  the statistics for that link.

     NGM_BRIDGE_GETCLR_STATS
	  Same as NGM_BRIDGE_GET_STATS,	but also atomically clears the statis-
	  tics as well.

     NGM_BRIDGE_GET_TABLE
	  Returns the current host mapping table used to direct	packets, in a
	  struct ng_bridge_host_ary.

     NGM_BRIDGE_SET_PERSISTENT
	  This command sets the	persistent flag	on the node, and takes no
	  arguments.

SHUTDOWN
     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when all hooks have been disconnected.  Setting the persistent flag via a
     NGM_BRIDGE_SET_PERSISTENT control message disables	automatic node shut-
     down when the last	hook gets disconnected.

FILES
     /usr/share/examples/netgraph/ether.bridge
	       Example script showing how to set up a bridging network

SEE ALSO
     if_bridge(4), netgraph(4),	ng_ether(4), ng_hub(4),	ng_one2many(4),
     ngctl(8)

HISTORY
     The ng_bridge node	type was implemented in	FreeBSD	4.2.

AUTHORS
     Archie Cobbs <archie@FreeBSD.org>

FreeBSD	9.2			  May 5, 2010			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | LOOP DETECTION | IPFW PROCESSING | HOOKS | CONTROL MESSAGES | SHUTDOWN | FILES | SEE ALSO | HISTORY | AUTHORS

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