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 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
(setconfig
)
- 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 */
uint32_t loopTimeout; /* link loopback mute time */
uint32_t maxStaleness; /* max host age before nuking */
uint32_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
(getconfig
)
- Returns the current configuration as a
struct
ng_bridge_config
.
NGM_BRIDGE_RESET
(reset
)
- Causes the node to forget all hosts and unmute all links. The node
configuration is not changed.
NGM_BRIDGE_GET_STATS
(getstats
)
- 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 {
uint64_t recvOctets; /* total octets rec'd on link */
uint64_t recvPackets; /* total pkts rec'd on link */
uint64_t recvMulticasts; /* multicast pkts rec'd on link */
uint64_t recvBroadcasts; /* broadcast pkts rec'd on link */
uint64_t recvUnknown; /* pkts rec'd with unknown dest addr */
uint64_t recvRunts; /* pkts rec'd less than 14 bytes */
uint64_t recvInvalid; /* pkts rec'd with bogus source addr */
uint64_t xmitOctets; /* total octets xmit'd on link */
uint64_t xmitPackets; /* total pkts xmit'd on link */
uint64_t xmitMulticasts; /* multicast pkts xmit'd on link */
uint64_t xmitBroadcasts; /* broadcast pkts xmit'd on link */
uint64_t loopDrops; /* pkts dropped due to loopback */
uint64_t loopDetects; /* number of loop detections */
uint64_t memoryFailures; /* times couldn't get mem or mbuf */
};
NGM_BRIDGE_CLR_STATS
(clrstats
)
- This command takes a four byte link number as an argument and clears the
statistics for that link.
NGM_BRIDGE_GETCLR_STATS
(getclrstats
)
- Same as
NGM_BRIDGE_GET_STATS
, but also
atomically clears the statistics as well.
NGM_BRIDGE_GET_TABLE
(gettable
)
- Returns the current host mapping table used to direct packets, in a
struct ng_bridge_host_ary
.
NGM_BRIDGE_SET_PERSISTENT
(setpersistent
)
- 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⟩