ng_bridge

NAME

ng_bridge — Ethernet bridging netgraph node type

SYNOPSIS

#include <sys/types.h>
#include <netgraph/ng_bridge.h>

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 an unlimited number of 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:

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:
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.