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freebsd-manpages_6.2-1_all 
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.
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.
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.
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.
SHUTDOWN
This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
when all hooks have been disconnected.
FILES
/usr/share/examples/netgraph/ether.bridge
Example script showing how to set up a bridging network
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〉