SYNOPSIS
In sys/types.h In netgraph/ng_bridge.hDESCRIPTION
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_ether4 nodes. To connect the host machine to a bridged network, simply connect the upper hook of an ng_ether4 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