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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 an unlimited number of hooks. Each connected hook represents a bridged link. The hooks are named .Ar link0 , .Ar link1 , etc. Typically these hooks are connected to the .Ar lower hooks of one or more .Xr ng_ether 4 nodes. To connect the host machine to a bridged network, simply connect the .Ar upper hook of an .Xr ng_ether 4 node to the bridge node. .Pp Instead of naming a hook .Ar linkX the hook might be also named .Ar uplinkX . The node does not learn MAC addresses on uplink hooks, which keeps the internal address table small. This way it is desirable to connect the .Ar lower hook of an .Xr ng_ether 4 node to an .Ar uplink hook of the bridge, and ignore the complexity of the outside world. Frames with unknown MACs are always sent out to .Ar uplink hooks, so no functionality is lost. The .Ar uplink0 hook is not allowed. .Pp The .Ar linkX and .Ar uplinkX hook numbers can be autoassigned. If a new hook name was specified as .Ar link or .Ar uplink the node will append lowest available valid number to the name of the new hook. .Pp Frames with unknown destination MAC addresses are replicated to any available hook, unless the first connected hook is an .Ar uplink hook. In this case the node assumes, that all unknown MAC addresses are located solely on the .Ar uplink hooks and only those hooks will be used to send out frames with unknown destination MACs. If the first connected hook is an .Ar link hook, the node will replicate such frames to all types of hooks, even if .Ar uplink hooks are connected later. .Sh CONTROL MESSAGES This node type supports the generic control messages, plus the following: .Bl -tag -width foo .It Dv NGM_BRIDGE_SET_CONFIG Pq Ar setconfig Set the node configuration. This command takes a .Vt "struct ng_bridge_config" as an argument: .Bd -literal -offset 0n /* Node configuration structure */ struct ng_bridge_config { 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 */ }; .Ed .Pp The .Va 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 .Va loopTimeout determines how long (in seconds) a looped link is muted. The default is 60 seconds. The .Va maxStaleness parameter determines how long a period of inactivity before a host's entry is forgotten. The default is 15 minutes. The .Va minStableAge determines how quickly a host must jump from one link to another before we declare a loopback condition. The default is one second. .It Dv NGM_BRIDGE_GET_CONFIG Pq Ar getconfig Returns the current configuration as a .Vt "struct ng_bridge_config" . .It Dv NGM_BRIDGE_RESET Pq Ar reset Causes the node to forget all hosts and unmute all links. The node configuration is not changed. .It Dv NGM_BRIDGE_GET_STATS Pq Ar getstats This command takes a four byte link number as an argument and returns a .Vt "struct ng_bridge_link_stats" containing statistics for the corresponding .Ar link , which must be currently connected: .Bd -literal -offset 0n /* 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 */ }; .Ed .Pp Negative numbers refer to the .Ar uplink hooks. So querying for -7 will get the statistics for hook .Ar uplink7 . .It Dv NGM_BRIDGE_CLR_STATS Pq Ar clrstats This command takes a four byte link number as an argument and clears the statistics for that link. .It Dv NGM_BRIDGE_GETCLR_STATS Pq Ar getclrstats Same as .Dv NGM_BRIDGE_GET_STATS , but also atomically clears the statistics as well. .It Dv NGM_BRIDGE_GET_TABLE Pq Ar gettable Returns the current host mapping table used to direct packets, in a .Vt "struct ng_bridge_host_ary" . .It Dv NGM_BRIDGE_SET_PERSISTENT Pq Ar setpersistent This command sets the persistent flag on the node, and takes no arguments. .It Dv NGM_BRIDGE_MOVE_HOST Pq Ar movehost This command takes a .Vt "struct ng_bridge_move_host" as an argument. It assigns the MAC .Va addr to the .Va hook . If the .Va hook is the empty string, the incoming hook of the control message is used as fallback. .Pp If necessary, the MAC is removed from the currently assigned hook and moved to the new one. If the MAC is moved faster than .Va minStableAge , the hook is considered as a loop and will block traffic for .Va loopTimeout seconds. .Bd -literal -offset 0n struct ng_bridge_move_host { u_char addr[ETHER_ADDR_LEN]; /* ethernet address */ char hook[NG_HOOKSIZ]; /* link where addr can be found */ }; .Ed .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 Mt archie@FreeBSD.org .Sh BUGS The .Nm node refuses to create the .Ar uplink0 hook to avoid later ambiguity with the .Dv NGM_BRIDGE_GET_STATS message.