NG_BRIDGE(4)						   BSD 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 performance.  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 net-
     work, 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 deter-
	  mines 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 corre-
	  sponding 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 statistics 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 shutdown 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>

BSD
								    May 5, 2010 							       BSD