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 al

ways forwards
every received packet to every other link.

LOOP DETECTION

The bridge node incorporates a simple loop detection algo

rithm. 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

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 be

fore 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, de

tected 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 minSta

bleAge determines
how quickly a host must jump from one link to another

before we
declare a loopback condition. The default is one sec

ond.

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 argu

ment 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 un

known 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 detec

tions */
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 argu

ment 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.

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

SEE ALSO

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 August 31, 2000

BSD