freebsd-skq/share/man/man4/ng_bridge.4

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.\" Author: Archie Cobbs <archie@FreeBSD.org>
.\"
.\" $FreeBSD$
.\"
.Dd May 5, 2010
.Dt NG_BRIDGE 4
.Os
.Sh NAME
.Nm ng_bridge
.Nd Ethernet bridging netgraph node type
.Sh SYNOPSIS
.In sys/types.h
.In netgraph/ng_bridge.h
.Sh DESCRIPTION
The
.Nm 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.
.Sh LOOP DETECTION
The
.Nm 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.
.Pp
A looped back link will be temporarily muted, i.e., all traffic
received on that link is ignored.
.Sh IPFW PROCESSING
Processing of IP packets via the
.Xr ipfirewall 4
mechanism on a per-link basis is not yet implemented.
.Sh HOOKS
This node type supports up to
.Dv NG_BRIDGE_MAX_LINKS
hooks.
Each connected hook represents a bridged link.
The hooks are named
.Dv link0 ,
.Dv link1 ,
etc.
Typically these hooks are connected to the
.Dv lower
hooks of one or more
.Xr ng_ether 4
nodes.
To connect the host machine to a bridged network, simply connect the
.Dv upper
hook of an
.Xr ng_ether 4
node to the bridge node.
.Sh CONTROL MESSAGES
This node type supports the generic control messages, plus the
following:
.Bl -tag -width foo
.It Dv NGM_BRIDGE_SET_CONFIG
Set the node configuration.
This command takes a
.Dv "struct ng_bridge_config"
as an argument:
.Bd -literal -offset 0n
/* 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 */
};
.Ed
.Pp
The
.Dv ipfw
array enables
.Xr ipfirewall 4
processing of IP packets received on the corresponding links.
The
.Dv debugLevel
field sets the debug level on the node.
At level of 2 or greater, detected loops are logged.
The default level is 1.
.Pp
The
.Dv loopTimeout
determines how long (in seconds) a looped link is muted.
The default is 60 seconds.
The
.Dv maxStaleness
parameter determines how long a period of inactivity before
a host's entry is forgotten.
The default is 15 minutes.
The
.Dv minStableAge
determines how quickly a host must jump from one link to another
before we declare a loopback condition.
The default is one second.
.Pp
.It Dv NGM_BRIDGE_GET_CONFIG
Returns the current configuration as a
.Dv "struct ng_bridge_config" .
.It Dv NGM_BRIDGE_RESET
Causes the node to forget all hosts and unmute all links.
The node configuration is not changed.
.It Dv NGM_BRIDGE_GET_STATS
This command takes a four byte link number as an argument and
returns a
.Dv "struct ng_bridge_link_stats"
containing statistics for the corresponding link, which must be
currently connected:
.Bd -literal -offset 0n
/* 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 */
};
.Ed
.It Dv NGM_BRIDGE_CLR_STATS
This command takes a four byte link number as an argument and
clears the statistics for that link.
.It Dv NGM_BRIDGE_GETCLR_STATS
Same as
.Dv NGM_BRIDGE_GET_STATS ,
but also atomically clears the statistics as well.
.It Dv NGM_BRIDGE_GET_TABLE
Returns the current host mapping table used to direct packets, in a
.Dv "struct ng_bridge_host_ary" .
.It Dv NGM_BRIDGE_SET_PERSISTENT
This command sets the persistent flag on the node, and takes no arguments.
.El
.Sh SHUTDOWN
This node shuts down upon receipt of a
.Dv NGM_SHUTDOWN
control message, or when all hooks have been disconnected.  Setting the
persistent flag via a
.Dv NGM_BRIDGE_SET_PERSISTENT
control message disables automatic node shutdown when the last hook gets
disconnected.
.Sh FILES
.Bl -tag -width XXXXXXXX -compact
.It Pa /usr/share/examples/netgraph/ether.bridge
Example script showing how to set up a bridging network
.El
.Sh SEE ALSO
.Xr if_bridge 4 ,
.Xr netgraph 4 ,
.Xr ng_ether 4 ,
.Xr ng_hub 4 ,
.Xr ng_one2many 4 ,
.Xr ngctl 8
.Sh HISTORY
The
.Nm
node type was implemented in
.Fx 4.2 .
.Sh AUTHORS
.An Archie Cobbs Aq archie@FreeBSD.org